[release-branch.go1.11] Merge branch 'master' into release-branch.go1.11

Change-Id: I4f09f847c7304e37df8388b45aa8d6281a677de3

52 files changed, 1088 insertions, 698 deletions

diff --git a/doc/code.html b/doc/code.html
index 4e8c54a1c5..b6d41ef68c 100644
--- a/doc/code.html
+++ b/doc/code.html
@@ -44,18 +44,16 @@ control repositories.
 <h3 id="Workspaces">Workspaces</h3>
 
 <p>
-A workspace is a directory hierarchy with three directories at its root:
+A workspace is a directory hierarchy with two directories at its root:
 </p>
 
 <ul>
-<li><code>src</code> contains Go source files,
-<li><code>pkg</code> contains package objects, and
+<li><code>src</code> contains Go source files, and
 <li><code>bin</code> contains executable commands.
 </ul>
 
 <p>
-The <code>go</code> tool builds source packages and installs the resulting
-binaries to the <code>pkg</code> and <code>bin</code> directories.
+The <code>go</code> tool builds and installs binaries to the <code>bin</code> directory.
 </p>
 
 <p>
@@ -72,10 +70,6 @@ To give you an idea of how a workspace looks in practice, here's an example:
 bin/
     hello                          # command executable
     outyet                         # command executable
-pkg/
-    linux_amd64/
-        github.com/golang/example/
-            stringutil.a           # package object
 src/
     <a href="https://github.com/golang/example/">github.com/golang/example/</a>
         .git/                      # Git repository metadata
@@ -374,9 +368,8 @@ $ <b>go build</b>
 </pre>
 
 <p>
-This won't produce an output file. To do that, you must use <code>go
-install</code>, which places the package object inside the <code>pkg</code>
-directory of the workspace.
+This won't produce an output file.
+Instead it saves the compiled package in the local build cache.
 </p>
 
 <p>
@@ -400,9 +393,7 @@ func main() {
 </pre>
 
 <p>
-Whenever the <code>go</code> tool installs a package or binary, it also
-installs whatever dependencies it has.
-So when you install the <code>hello</code> program
+Install the <code>hello</code> program:
 </p>
 
 <pre>
@@ -410,10 +401,6 @@ $ <b>go install github.com/user/hello</b>
 </pre>
 
 <p>
-the <code>stringutil</code> package will be installed as well, automatically.
-</p>
-
-<p>
 Running the new version of the program, you should see a new, reversed message:
 </p>
 
@@ -429,10 +416,6 @@ After the steps above, your workspace should look like this:
 <pre>
 bin/
     hello                 # command executable
-pkg/
-    linux_amd64/          # this will reflect your OS and architecture
-        github.com/user/
-            stringutil.a  # package object
 src/
     github.com/user/
         hello/
@@ -441,22 +424,6 @@ src/
             reverse.go    # package source
 </pre>
 
-<p>
-Note that <code>go install</code> placed the <code>stringutil.a</code> object
-in a directory inside <code>pkg/linux_amd64</code> that mirrors its source
-directory.
-This is so that future invocations of the <code>go</code> tool can find the
-package object and avoid recompiling the package unnecessarily.
-The <code>linux_amd64</code> part is there to aid in cross-compilation,
-and will reflect the operating system and architecture of your system.
-</p>
-
-<p>
-Go command executables are statically linked; the package objects need not
-be present to run Go programs.
-</p>
-
-
 <h3 id="PackageNames">Package names</h3>
 
 <p>
@@ -597,12 +564,6 @@ tree should now look like this:
 <pre>
 bin/
     hello                           # command executable
-pkg/
-    linux_amd64/
-        github.com/golang/example/
-            stringutil.a            # package object
-        github.com/user/
-            stringutil.a            # package object
 src/
     github.com/golang/example/
 	.git/                       # Git repository metadata
diff --git a/doc/go1.11.html b/doc/go1.11.html
index a1249db475..fae1c5ff14 100644
--- a/doc/go1.11.html
+++ b/doc/go1.11.html
@@ -167,7 +167,18 @@ Do not send CLs removing the interior tags from such phrases.
 <h3 id="gopackages">Package loading</h3>
 
 <p>
-  TODO: Note about go/build versus golang.org/x/tools/go/packages.
+  The new package
+  <a href="https://godoc.org/golang.org/x/tools/go/packages"><code>golang.org/x/tools/go/packages</code></a>
+  provides a simple API for locating and loading packages of Go source code.
+  Although not yet part of the standard library, for many tasks it
+  effectively replaces the <a href="/pkg/go/build"><code>go/build</code></a>
+  package, whose API is unable to fully support modules.
+  Because it runs an external query command such as
+  <a href="/cmd/go/#hdr-List_packages"><code>go list</code></a>
+  to obtain information about Go packages, it enables the construction of
+  analysis tools that work equally well with alternative build systems
+  such as <a href="https://bazel.build">Bazel</a>
+  and <a href="https://buckbuild.com">Buck</a>.
 </p>
 
 <h3 id="gocache">Build cache requirement</h3>
@@ -262,9 +273,8 @@ func f(v interface{}) {
 
   This is useful, for example, to call <code>String</code> methods
   when paused at a breakpoint.
-  <!-- TODO(austin): Make sure methods calls are actually supported by Delve -->
 
-  This is currently only supported by Delve.
+  This is currently only supported by Delve (version 1.1.0 and up).
 </p>
 
 <h3 id="test">Test</h3>
@@ -793,7 +803,7 @@ for k := range m {
 
 <!-- CL 101715 was reverted -->
 
-<dl id="runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
+<dl id="runtime-again"><dt><a href="/pkg/runtime/">runtime</a></dt>
   <dd>
 
     <p><!-- CL 70993 -->
diff --git a/src/cmd/compile/internal/gc/reflect.go b/src/cmd/compile/internal/gc/reflect.go
index b9124b6317..935c3b0503 100644
--- a/src/cmd/compile/internal/gc/reflect.go
+++ b/src/cmd/compile/internal/gc/reflect.go
@@ -34,8 +34,9 @@ type ptabEntry struct {
 
 // runtime interface and reflection data structures
 var (
-	signatsetmu sync.Mutex // protects signatset
+	signatmu    sync.Mutex // protects signatset and signatslice
 	signatset   = make(map[*types.Type]struct{})
+	signatslice []*types.Type
 
 	itabs []itabEntry
 	ptabs []ptabEntry
@@ -960,9 +961,9 @@ func typesymprefix(prefix string, t *types.Type) *types.Sym {
 
 	// This function is for looking up type-related generated functions
 	// (e.g. eq and hash). Make sure they are indeed generated.
-	signatsetmu.Lock()
+	signatmu.Lock()
 	addsignat(t)
-	signatsetmu.Unlock()
+	signatmu.Unlock()
 
 	//print("algsym: %s -> %+S\n", p, s);
 
@@ -974,9 +975,9 @@ func typenamesym(t *types.Type) *types.Sym {
 		Fatalf("typenamesym %v", t)
 	}
 	s := typesym(t)
-	signatsetmu.Lock()
+	signatmu.Lock()
 	addsignat(t)
-	signatsetmu.Unlock()
+	signatmu.Unlock()
 	return s
 }
 
@@ -1447,7 +1448,10 @@ func itabsym(it *obj.LSym, offset int64) *obj.LSym {
 
 // addsignat ensures that a runtime type descriptor is emitted for t.
 func addsignat(t *types.Type) {
-	signatset[t] = struct{}{}
+	if _, ok := signatset[t]; !ok {
+		signatset[t] = struct{}{}
+		signatslice = append(signatslice, t)
+	}
 }
 
 func addsignats(dcls []*Node) {
@@ -1462,14 +1466,15 @@ func addsignats(dcls []*Node) {
 func dumpsignats() {
 	// Process signatset. Use a loop, as dtypesym adds
 	// entries to signatset while it is being processed.
-	signats := make([]typeAndStr, len(signatset))
-	for len(signatset) > 0 {
+	signats := make([]typeAndStr, len(signatslice))
+	for len(signatslice) > 0 {
 		signats = signats[:0]
 		// Transfer entries to a slice and sort, for reproducible builds.
-		for t := range signatset {
+		for _, t := range signatslice {
 			signats = append(signats, typeAndStr{t: t, short: typesymname(t), regular: t.String()})
 			delete(signatset, t)
 		}
+		signatslice = signatslice[:0]
 		sort.Sort(typesByString(signats))
 		for _, ts := range signats {
 			t := ts.t
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 553713a1e9..af43da6275 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -3515,6 +3515,10 @@ func (s *state) call(n *Node, k callKind) *ssa.Value {
 			break
 		}
 		closure = s.expr(fn)
+		if thearch.LinkArch.Family == sys.Wasm {
+			// TODO(neelance): On other architectures this should be eliminated by the optimization steps
+			s.nilCheck(closure)
+		}
 	case OCALLMETH:
 		if fn.Op != ODOTMETH {
 			Fatalf("OCALLMETH: n.Left not an ODOTMETH: %v", fn)
diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 1292596697..c67e3f5a1c 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -40,6 +40,7 @@
 // 	cache       build and test caching
 // 	environment environment variables
 // 	filetype    file types
+// 	go.mod      the go.mod file
 // 	gopath      GOPATH environment variable
 // 	gopath-get  legacy GOPATH go get
 // 	goproxy     module proxy protocol
@@ -622,24 +623,25 @@
 // to -f '{{.ImportPath}}'. The struct being passed to the template is:
 //
 //     type Package struct {
-//         Dir           string  // directory containing package sources
-//         ImportPath    string  // import path of package in dir
-//         ImportComment string  // path in import comment on package statement
-//         Name          string  // package name
-//         Doc           string  // package documentation string
-//         Target        string  // install path
-//         Shlib         string  // the shared library that contains this package (only set when -linkshared)
-//         Goroot        bool    // is this package in the Go root?
-//         Standard      bool    // is this package part of the standard Go library?
-//         Stale         bool    // would 'go install' do anything for this package?
-//         StaleReason   string  // explanation for Stale==true
-//         Root          string  // Go root or Go path dir containing this package
-//         ConflictDir   string  // this directory shadows Dir in $GOPATH
-//         BinaryOnly    bool    // binary-only package: cannot be recompiled from sources
-//         ForTest       string  // package is only for use in named test
-//         DepOnly       bool    // package is only a dependency, not explicitly listed
-//         Export        string  // file containing export data (when using -export)
-//         Module        *Module // info about package's containing module, if any (can be nil)
+//         Dir           string   // directory containing package sources
+//         ImportPath    string   // import path of package in dir
+//         ImportComment string   // path in import comment on package statement
+//         Name          string   // package name
+//         Doc           string   // package documentation string
+//         Target        string   // install path
+//         Shlib         string   // the shared library that contains this package (only set when -linkshared)
+//         Goroot        bool     // is this package in the Go root?
+//         Standard      bool     // is this package part of the standard Go library?
+//         Stale         bool     // would 'go install' do anything for this package?
+//         StaleReason   string   // explanation for Stale==true
+//         Root          string   // Go root or Go path dir containing this package
+//         ConflictDir   string   // this directory shadows Dir in $GOPATH
+//         BinaryOnly    bool     // binary-only package: cannot be recompiled from sources
+//         ForTest       string   // package is only for use in named test
+//         Export        string   // file containing export data (when using -export)
+//         Module        *Module  // info about package's containing module, if any (can be nil)
+//         Match         []string // command-line patterns matching this package
+//         DepOnly       bool     // package is only a dependency, not explicitly listed
 //
 //         // Source files
 //         GoFiles         []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
@@ -722,7 +724,8 @@
 // The -compiled flag causes list to set CompiledGoFiles to the Go source
 // files presented to the compiler. Typically this means that it repeats
 // the files listed in GoFiles and then also adds the Go code generated
-// by processing CgoFiles and SwigFiles.
+// by processing CgoFiles and SwigFiles. The Imports list contains the
+// union of all imports from both GoFiles and CompiledGoFiles.
 //
 // The -deps flag causes list to iterate over not just the named packages
 // but also all their dependencies. It visits them in a depth-first post-order
@@ -842,7 +845,7 @@
 // module paths match the pattern.
 // A query of the form path@version specifies the result of that query,
 // which is not limited to active modules.
-// See 'go help module' for more about module queries.
+// See 'go help modules' for more about module queries.
 //
 // The template function "module" takes a single string argument
 // that must be a module path or query and returns the specified
@@ -873,7 +876,6 @@
 //
 // 	download    download modules to local cache
 // 	edit        edit go.mod from tools or scripts
-// 	fix         make go.mod semantically consistent
 // 	graph       print module requirement graph
 // 	init        initialize new module in current directory
 // 	tidy        add missing and remove unused modules
@@ -912,7 +914,7 @@
 //         Dir     string // absolute path to cached source root directory
 //     }
 //
-// See 'go help module' for more about module queries.
+// See 'go help modules' for more about module queries.
 //
 //
 // Edit go.mod from tools or scripts
@@ -997,52 +999,6 @@
 // by invoking 'go mod edit' with -require, -exclude, and so on.
 //
 //
-// Make go.mod semantically consistent
-//
-// Usage:
-//
-// 	go mod fix
-//
-// Fix updates go.mod to use canonical version identifiers and
-// to be semantically consistent. For example, consider this go.mod file:
-//
-// 	module M
-//
-// 	require (
-// 		A v1
-// 		B v1.0.0
-// 		C v1.0.0
-// 		D v1.2.3
-// 		E dev
-// 	)
-//
-// 	exclude D v1.2.3
-//
-// First, fix rewrites non-canonical version identifiers to semver form, so
-// A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the latest
-// commit on the dev branch, perhaps v0.0.0-20180523231146-b3f5c0f6e5f1.
-//
-// Next, fix updates requirements to respect exclusions, so the requirement
-// on the excluded D v1.2.3 is updated to use the next available version of D,
-// perhaps D v1.2.4 or D v1.3.0.
-//
-// Finally, fix removes redundant or misleading requirements.
-// For example, if A v1.0.0 itself requires B v1.2.0 and C v1.0.0, then go.mod's
-// requirement of B v1.0.0 is misleading (superseded by A's need for v1.2.0),
-// and its requirement of C v1.0.0 is redundant (implied by A's need for the
-// same version), so both will be removed. If module M contains packages
-// that directly import packages from B or C, then the requirements will be
-// kept but updated to the actual versions being used.
-//
-// Although fix runs the fix-up operation in isolation, the fix-up also
-// runs automatically any time a go command uses the module graph,
-// to update go.mod to reflect reality. Because the module graph defines
-// the meaning of import statements, any commands that load packages
-// also use and therefore fix the module graph. For example,
-// go build, go get, go install, go list, go test, go mod graph, go mod tidy,
-// and other commands all effectively imply go mod fix.
-//
-//
 // Print module requirement graph
 //
 // Usage:
@@ -1619,6 +1575,73 @@
 // command.
 //
 //
+// The go.mod file
+//
+// A module version is defined by a tree of source files, with a go.mod
+// file in its root. When the go command is run, it looks in the current
+// directory and then successive parent directories to find the go.mod
+// marking the root of the main (current) module.
+//
+// The go.mod file itself is line-oriented, with // comments but
+// no /* */ comments. Each line holds a single directive, made up of a
+// verb followed by arguments. For example:
+//
+// 	module my/thing
+// 	require other/thing v1.0.2
+// 	require new/thing v2.3.4
+// 	exclude old/thing v1.2.3
+// 	replace bad/thing v1.4.5 => good/thing v1.4.5
+//
+// The verbs are module, to define the module path; require, to require
+// a particular module at a given version or later; exclude, to exclude
+// a particular module version from use; and replace, to replace a module
+// version with a different module version. Exclude and replace apply only
+// in the main module's go.mod and are ignored in dependencies.
+// See https://research.swtch.com/vgo-mvs for details.
+//
+// The leading verb can be factored out of adjacent lines to create a block,
+// like in Go imports:
+//
+// 	require (
+// 		new/thing v2.3.4
+// 		old/thing v1.2.3
+// 	)
+//
+// The go.mod file is designed both to be edited directly and to be
+// easily updated by tools. The 'go mod edit' command can be used to
+// parse and edit the go.mod file from programs and tools.
+// See 'go help mod edit'.
+//
+// The go command automatically updates go.mod each time it uses the
+// module graph, to make sure go.mod always accurately reflects reality
+// and is properly formatted.
+//
+// The update rewrites non-canonical version identifiers to semver form,
+// so A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the
+// latest commit on the dev branch, perhaps v0.0.0-20180523231146-b3f5c0f6e5f1.
+//
+// The update modifies requirements to respect exclusions, so the
+// requirement on the excluded D v1.2.3 is updated to use the next
+// available version of D, perhaps D v1.2.4 or D v1.3.0.
+//
+// The update removes redundant or misleading requirements.
+// For example, if A v1.0.0 itself requires B v1.2.0 and C v1.0.0,
+// then go.mod's requirement of B v1.0.0 is misleading (superseded by
+// A's need for v1.2.0), and its requirement of C v1.0.0 is redundant
+// (implied by A's need for the same version), so both will be removed.
+// If module M contains packages that directly import packages from B or
+// C, then the requirements will be kept but updated to the actual
+// versions being used.
+//
+// Finally, the update reformats the go.mod in a canonical formatting, so
+// that future mechanical changes will result in minimal diffs.
+//
+// Because the module graph defines the meaning of import statements, any
+// commands that load packages also use and therefore update go.mod,
+// including go build, go get, go install, go list, go test, go mod graph,
+// go mod tidy, and go mod why.
+//
+//
 // GOPATH environment variable
 //
 // The Go path is used to resolve import statements.
@@ -2094,7 +2117,7 @@
 // The go.mod file can also specify replacements and excluded versions
 // that only apply when building the module directly; they are ignored
 // when the module is incorporated into a larger build.
-// For more about the go.mod file, see https://research.swtch.com/vgo-module.
+// For more about the go.mod file, see 'go help go.mod'.
 //
 // To start a new module, simply create a go.mod file in the root of the
 // module's directory tree, containing only a module statement.
@@ -2349,8 +2372,6 @@
 // about how source code in version control systems is mapped to
 // module file trees.
 //
-// TODO: Add documentation to go command.
-//
 // Module downloading and verification
 //
 // The go command maintains, in the main module's root directory alongside
diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index debe4867e6..85cae90f87 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -1291,6 +1291,7 @@ func TestGetGitDefaultBranch(t *testing.T) {
 	tg.grepStdout(`\* another-branch`, "not on correct default branch")
 }
 
+// Security issue. Don't disable. See golang.org/issue/22125.
 func TestAccidentalGitCheckout(t *testing.T) {
 	testenv.MustHaveExternalNetwork(t)
 	if _, err := exec.LookPath("git"); err != nil {
@@ -1301,13 +1302,17 @@ func TestAccidentalGitCheckout(t *testing.T) {
 	defer tg.cleanup()
 	tg.parallel()
 	tg.tempDir("src")
+
 	tg.setenv("GOPATH", tg.path("."))
 
 	tg.runFail("get", "-u", "vcs-test.golang.org/go/test1-svn-git")
 	tg.grepStderr("src[\\\\/]vcs-test.* uses git, but parent .*src[\\\\/]vcs-test.* uses svn", "get did not fail for right reason")
 
-	tg.runFail("get", "-u", "vcs-test.golang.org/go/test2-svn-git/test2main")
-	tg.grepStderr("src[\\\\/]vcs-test.* uses git, but parent .*src[\\\\/]vcs-test.* uses svn", "get did not fail for right reason")
+	if _, err := os.Stat(tg.path("SrC")); err == nil {
+		// This case only triggers on a case-insensitive file system.
+		tg.runFail("get", "-u", "vcs-test.golang.org/go/test2-svn-git/test2main")
+		tg.grepStderr("src[\\\\/]vcs-test.* uses git, but parent .*src[\\\\/]vcs-test.* uses svn", "get did not fail for right reason")
+	}
 }
 
 func TestErrorMessageForSyntaxErrorInTestGoFileSaysFAIL(t *testing.T) {
@@ -3527,24 +3532,43 @@ func TestImportLocal(t *testing.T) {
 }
 
 func TestGoGetInsecure(t *testing.T) {
-	testenv.MustHaveExternalNetwork(t)
+	test := func(t *testing.T, modules bool) {
+		testenv.MustHaveExternalNetwork(t)
 
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.makeTempdir()
-	tg.setenv("GOPATH", tg.path("."))
-	tg.failSSH()
+		tg := testgo(t)
+		defer tg.cleanup()
+		tg.makeTempdir()
+		tg.failSSH()
 
-	const repo = "insecure.go-get-issue-15410.appspot.com/pkg/p"
+		if modules {
+			tg.setenv("GOPATH", tg.path("gp"))
+			tg.tempFile("go.mod", "module m")
+			tg.cd(tg.path("."))
+			tg.setenv("GO111MODULE", "on")
+		} else {
+			tg.setenv("GOPATH", tg.path("."))
+			tg.setenv("GO111MODULE", "off")
+		}
 
-	// Try go get -d of HTTP-only repo (should fail).
-	tg.runFail("get", "-d", repo)
+		const repo = "insecure.go-get-issue-15410.appspot.com/pkg/p"
 
-	// Try again with -insecure (should succeed).
-	tg.run("get", "-d", "-insecure", repo)
+		// Try go get -d of HTTP-only repo (should fail).
+		tg.runFail("get", "-d", repo)
+
+		// Try again with -insecure (should succeed).
+		tg.run("get", "-d", "-insecure", repo)
+
+		// Try updating without -insecure (should fail).
+		tg.runFail("get", "-d", "-u", "-f", repo)
 
-	// Try updating without -insecure (should fail).
-	tg.runFail("get", "-d", "-u", "-f", repo)
+		if modules {
+			tg.run("list", "-m", "...")
+			tg.grepStdout("insecure.go-get-issue", "should find insecure module")
+		}
+	}
+
+	t.Run("gopath", func(t *testing.T) { test(t, false) })
+	t.Run("modules", func(t *testing.T) { test(t, true) })
 }
 
 func TestGoGetUpdateInsecure(t *testing.T) {
@@ -4187,9 +4211,10 @@ func TestGoGetUpdateWithWildcard(t *testing.T) {
 	tg.setenv("GOPATH", tg.path("."))
 	const aPkgImportPath = "github.com/tmwh/go-get-issue-14450/a"
 	tg.run("get", aPkgImportPath)
-	tg.run("get", "-u", ".../")
-	tg.grepStderrNot("cannot find package", "did not update packages given wildcard path")
+	tg.runFail("get", "-u", ".../")
+	tg.grepStderr("cannot find package.*d-dependency/e", "should have detected e missing")
 
+	// Even though get -u failed, the source for others should be downloaded.
 	var expectedPkgPaths = []string{
 		"src/github.com/tmwh/go-get-issue-14450/b",
 		"src/github.com/tmwh/go-get-issue-14450-b-dependency/c",
@@ -5647,37 +5672,6 @@ func TestRelativePkgdir(t *testing.T) {
 	tg.run("build", "-i", "-pkgdir=.", "runtime")
 }
 
-func TestGcflagsPatterns(t *testing.T) {
-	skipIfGccgo(t, "gccgo has no standard packages")
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.setenv("GOPATH", "")
-	tg.setenv("GOCACHE", "off")
-
-	tg.run("build", "-n", "-v", "-gcflags= \t\r\n -e", "fmt")
-	tg.grepStderr("^# fmt", "did not rebuild fmt")
-	tg.grepStderrNot("^# reflect", "incorrectly rebuilt reflect")
-
-	tg.run("build", "-n", "-v", "-gcflags=-e", "fmt", "reflect")
-	tg.grepStderr("^# fmt", "did not rebuild fmt")
-	tg.grepStderr("^# reflect", "did not rebuild reflect")
-	tg.grepStderrNot("^# runtime", "incorrectly rebuilt runtime")
-
-	tg.run("build", "-n", "-x", "-v", "-gcflags= \t\r\n reflect \t\r\n = \t\r\n -N", "fmt")
-	tg.grepStderr("^# fmt", "did not rebuild fmt")
-	tg.grepStderr("^# reflect", "did not rebuild reflect")
-	tg.grepStderr("compile.* -N .*-p reflect", "did not build reflect with -N flag")
-	tg.grepStderrNot("compile.* -N .*-p fmt", "incorrectly built fmt with -N flag")
-
-	tg.run("test", "-c", "-n", "-gcflags=-N", "-ldflags=-X=x.y=z", "strings")
-	tg.grepStderr("compile.* -N .*compare_test.go", "did not compile strings_test package with -N flag")
-	tg.grepStderr("link.* -X=x.y=z", "did not link strings.test binary with -X flag")
-
-	tg.run("test", "-c", "-n", "-gcflags=strings=-N", "-ldflags=strings=-X=x.y=z", "strings")
-	tg.grepStderr("compile.* -N .*compare_test.go", "did not compile strings_test package with -N flag")
-	tg.grepStderr("link.* -X=x.y=z", "did not link strings.test binary with -X flag")
-}
-
 func TestGoTestMinusN(t *testing.T) {
 	// Intent here is to verify that 'go test -n' works without crashing.
 	// This reuses flag_test.go, but really any test would do.
diff --git a/src/cmd/go/internal/get/get.go b/src/cmd/go/internal/get/get.go
index fd97c6dcb6..e4148bceb0 100644
--- a/src/cmd/go/internal/get/get.go
+++ b/src/cmd/go/internal/get/get.go
@@ -163,9 +163,8 @@ func runGet(cmd *base.Command, args []string) {
 	if *getT {
 		mode |= load.GetTestDeps
 	}
-	args = downloadPaths(args)
-	for _, arg := range args {
-		download(arg, nil, &stk, mode)
+	for _, pkg := range downloadPaths(args) {
+		download(pkg, nil, &stk, mode)
 	}
 	base.ExitIfErrors()
 
@@ -184,8 +183,7 @@ func runGet(cmd *base.Command, args []string) {
 	// This leads to duplicated loads of the standard packages.
 	load.ClearCmdCache()
 
-	args = load.ImportPaths(args)
-	load.PackagesForBuild(args)
+	pkgs := load.PackagesForBuild(args)
 
 	// Phase 3. Install.
 	if *getD {
@@ -195,7 +193,7 @@ func runGet(cmd *base.Command, args []string) {
 		return
 	}
 
-	work.InstallPackages(args)
+	work.InstallPackages(args, pkgs)
 }
 
 // downloadPaths prepares the list of paths to pass to download.
@@ -203,34 +201,21 @@ func runGet(cmd *base.Command, args []string) {
 // for a particular pattern, downloadPaths leaves it in the result list,
 // in the hope that we can figure out the repository from the
 // initial ...-free prefix.
-func downloadPaths(args []string) []string {
-	for _, arg := range args {
+func downloadPaths(patterns []string) []string {
+	for _, arg := range patterns {
 		if strings.Contains(arg, "@") {
 			base.Fatalf("go: cannot use path@version syntax in GOPATH mode")
 		}
 	}
-
-	args = load.ImportPathsForGoGet(args)
-	var out []string
-	for _, a := range args {
-		if strings.Contains(a, "...") {
-			var expand []string
-			// Use matchPackagesInFS to avoid printing
-			// warnings. They will be printed by the
-			// eventual call to importPaths instead.
-			if build.IsLocalImport(a) {
-				expand = search.MatchPackagesInFS(a)
-			} else {
-				expand = search.MatchPackages(a)
-			}
-			if len(expand) > 0 {
-				out = append(out, expand...)
-				continue
-			}
+	var pkgs []string
+	for _, m := range search.ImportPathsQuiet(patterns) {
+		if len(m.Pkgs) == 0 && strings.Contains(m.Pattern, "...") {
+			pkgs = append(pkgs, m.Pattern)
+		} else {
+			pkgs = append(pkgs, m.Pkgs...)
 		}
-		out = append(out, a)
 	}
-	return out
+	return pkgs
 }
 
 // downloadCache records the import paths we have already
@@ -255,7 +240,7 @@ func download(arg string, parent *load.Package, stk *load.ImportStack, mode int)
 	}
 	load1 := func(path string, mode int) *load.Package {
 		if parent == nil {
-			return load.LoadPackage(path, stk)
+			return load.LoadPackageNoFlags(path, stk)
 		}
 		return load.LoadImport(path, parent.Dir, parent, stk, nil, mode|load.ResolveModule)
 	}
@@ -311,9 +296,9 @@ func download(arg string, parent *load.Package, stk *load.ImportStack, mode int)
 		// for p has been replaced in the package cache.
 		if wildcardOkay && strings.Contains(arg, "...") {
 			if build.IsLocalImport(arg) {
-				args = search.MatchPackagesInFS(arg)
+				args = search.MatchPackagesInFS(arg).Pkgs
 			} else {
-				args = search.MatchPackages(arg)
+				args = search.MatchPackages(arg).Pkgs
 			}
 			isWildcard = true
 		}
@@ -344,7 +329,7 @@ func download(arg string, parent *load.Package, stk *load.ImportStack, mode int)
 			base.Run(cfg.BuildToolexec, str.StringList(base.Tool("fix"), files))
 
 			// The imports might have changed, so reload again.
-			p = load.ReloadPackage(arg, stk)
+			p = load.ReloadPackageNoFlags(arg, stk)
 			if p.Error != nil {
 				base.Errorf("%s", p.Error)
 				return
diff --git a/src/cmd/go/internal/imports/scan.go b/src/cmd/go/internal/imports/scan.go
index 095bb64a8d..d944e95724 100644
--- a/src/cmd/go/internal/imports/scan.go
+++ b/src/cmd/go/internal/imports/scan.go
@@ -37,6 +37,7 @@ func scanFiles(files []string, tags map[string]bool, explicitFiles bool) ([]stri
 	imports := make(map[string]bool)
 	testImports := make(map[string]bool)
 	numFiles := 0
+Files:
 	for _, name := range files {
 		r, err := os.Open(name)
 		if err != nil {
@@ -48,6 +49,19 @@ func scanFiles(files []string, tags map[string]bool, explicitFiles bool) ([]stri
 		if err != nil {
 			return nil, nil, fmt.Errorf("reading %s: %v", name, err)
 		}
+
+		// import "C" is implicit requirement of cgo tag.
+		// When listing files on the command line (explicitFiles=true)
+		// we do not apply build tag filtering but we still do apply
+		// cgo filtering, so no explicitFiles check here.
+		// Why? Because we always have, and it's not worth breaking
+		// that behavior now.
+		for _, path := range list {
+			if path == `"C"` && !tags["cgo"] && !tags["*"] {
+				continue Files
+			}
+		}
+
 		if !explicitFiles && !ShouldBuild(data, tags) {
 			continue
 		}
diff --git a/src/cmd/go/internal/list/list.go b/src/cmd/go/internal/list/list.go
index e75270fa55..186b006c12 100644
--- a/src/cmd/go/internal/list/list.go
+++ b/src/cmd/go/internal/list/list.go
@@ -47,24 +47,25 @@ syntax of package template. The default output is equivalent
 to -f '{{.ImportPath}}'. The struct being passed to the template is:
 
     type Package struct {
-        Dir           string  // directory containing package sources
-        ImportPath    string  // import path of package in dir
-        ImportComment string  // path in import comment on package statement
-        Name          string  // package name
-        Doc           string  // package documentation string
-        Target        string  // install path
-        Shlib         string  // the shared library that contains this package (only set when -linkshared)
-        Goroot        bool    // is this package in the Go root?
-        Standard      bool    // is this package part of the standard Go library?
-        Stale         bool    // would 'go install' do anything for this package?
-        StaleReason   string  // explanation for Stale==true
-        Root          string  // Go root or Go path dir containing this package
-        ConflictDir   string  // this directory shadows Dir in $GOPATH
-        BinaryOnly    bool    // binary-only package: cannot be recompiled from sources
-        ForTest       string  // package is only for use in named test
-        DepOnly       bool    // package is only a dependency, not explicitly listed
-        Export        string  // file containing export data (when using -export)
-        Module        *Module // info about package's containing module, if any (can be nil)
+        Dir           string   // directory containing package sources
+        ImportPath    string   // import path of package in dir
+        ImportComment string   // path in import comment on package statement
+        Name          string   // package name
+        Doc           string   // package documentation string
+        Target        string   // install path
+        Shlib         string   // the shared library that contains this package (only set when -linkshared)
+        Goroot        bool     // is this package in the Go root?
+        Standard      bool     // is this package part of the standard Go library?
+        Stale         bool     // would 'go install' do anything for this package?
+        StaleReason   string   // explanation for Stale==true
+        Root          string   // Go root or Go path dir containing this package
+        ConflictDir   string   // this directory shadows Dir in $GOPATH
+        BinaryOnly    bool     // binary-only package: cannot be recompiled from sources
+        ForTest       string   // package is only for use in named test
+        Export        string   // file containing export data (when using -export)
+        Module        *Module  // info about package's containing module, if any (can be nil)
+        Match         []string // command-line patterns matching this package
+        DepOnly       bool     // package is only a dependency, not explicitly listed
 
         // Source files
         GoFiles         []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
@@ -268,7 +269,7 @@ A pattern containing "..." specifies the active modules whose
 module paths match the pattern.
 A query of the form path@version specifies the result of that query,
 which is not limited to active modules.
-See 'go help module' for more about module queries.
+See 'go help modules' for more about module queries.
 
 The template function "module" takes a single string argument
 that must be a module path or query and returns the specified
diff --git a/src/cmd/go/internal/load/flag.go b/src/cmd/go/internal/load/flag.go
index d9177b0de3..7534e65f54 100644
--- a/src/cmd/go/internal/load/flag.go
+++ b/src/cmd/go/internal/load/flag.go
@@ -6,7 +6,6 @@ package load
 
 import (
 	"cmd/go/internal/base"
-	"cmd/go/internal/search"
 	"cmd/go/internal/str"
 	"fmt"
 	"strings"
@@ -92,52 +91,3 @@ func (f *PerPackageFlag) For(p *Package) []string {
 	}
 	return flags
 }
-
-var (
-	cmdlineMatchers        []func(*Package) bool
-	cmdlineMatcherLiterals []func(*Package) bool
-)
-
-// SetCmdlinePatterns records the set of patterns given on the command line,
-// for use by the PerPackageFlags.
-func SetCmdlinePatterns(args []string) {
-	setCmdlinePatterns(args, base.Cwd)
-}
-
-func setCmdlinePatterns(args []string, cwd string) {
-	if len(args) == 0 {
-		args = []string{"."}
-	}
-	cmdlineMatchers = nil // allow reset for testing
-	cmdlineMatcherLiterals = nil
-	for _, arg := range args {
-		cmdlineMatchers = append(cmdlineMatchers, MatchPackage(arg, cwd))
-	}
-	for _, arg := range args {
-		if !strings.Contains(arg, "...") && !search.IsMetaPackage(arg) {
-			cmdlineMatcherLiterals = append(cmdlineMatcherLiterals, MatchPackage(arg, cwd))
-		}
-	}
-}
-
-// isCmdlinePkg reports whether p is a package listed on the command line.
-func isCmdlinePkg(p *Package) bool {
-	for _, m := range cmdlineMatchers {
-		if m(p) {
-			return true
-		}
-	}
-	return false
-}
-
-// isCmdlinePkgLiteral reports whether p is a package listed as
-// a literal package argument on the command line
-// (as opposed to being the result of expanding a wildcard).
-func isCmdlinePkgLiteral(p *Package) bool {
-	for _, m := range cmdlineMatcherLiterals {
-		if m(p) {
-			return true
-		}
-	}
-	return false
-}
diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
index bef27b33ad..ec2fa730c6 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -35,10 +35,11 @@ var (
 	ModBinDir            func() string                                       // return effective bin directory
 	ModLookup            func(path string) (dir, realPath string, err error) // lookup effective meaning of import
 	ModPackageModuleInfo func(path string) *modinfo.ModulePublic             // return module info for Package struct
-	ModImportPaths       func(args []string) []string                        // expand import paths
+	ModImportPaths       func(args []string) []*search.Match                 // expand import paths
 	ModPackageBuildInfo  func(main string, deps []string) string             // return module info to embed in binary
 	ModInfoProg          func(info string) []byte                            // wrap module info in .go code for binary
 	ModImportFromFiles   func([]string)                                      // update go.mod to add modules for imports in these files
+	ModDirImportPath     func(string) string                                 // return effective import path for directory
 )
 
 var IgnoreImports bool // control whether we ignore imports in packages
@@ -60,15 +61,17 @@ type PackagePublic struct {
 	Doc           string                `json:",omitempty"` // package documentation string
 	Target        string                `json:",omitempty"` // installed target for this package (may be executable)
 	Shlib         string                `json:",omitempty"` // the shared library that contains this package (only set when -linkshared)
-	Goroot        bool                  `json:",omitempty"` // is this package found in the Go root?
-	Standard      bool                  `json:",omitempty"` // is this package part of the standard Go library?
 	Root          string                `json:",omitempty"` // Go root or Go path dir containing this package
 	ConflictDir   string                `json:",omitempty"` // Dir is hidden by this other directory
-	BinaryOnly    bool                  `json:",omitempty"` // package cannot be recompiled
 	ForTest       string                `json:",omitempty"` // package is only for use in named test
-	DepOnly       bool                  `json:",omitempty"` // package is only as a dependency, not explicitly listed
 	Export        string                `json:",omitempty"` // file containing export data (set by go list -export)
 	Module        *modinfo.ModulePublic `json:",omitempty"` // info about package's module, if any
+	Match         []string              `json:",omitempty"` // command-line patterns matching this package
+	Goroot        bool                  `json:",omitempty"` // is this package found in the Go root?
+	Standard      bool                  `json:",omitempty"` // is this package part of the standard Go library?
+	DepOnly       bool                  `json:",omitempty"` // package is only as a dependency, not explicitly listed
+	BinaryOnly    bool                  `json:",omitempty"` // package cannot be recompiled
+	Incomplete    bool                  `json:",omitempty"` // was there an error loading this package or dependencies?
 
 	// Stale and StaleReason remain here *only* for the list command.
 	// They are only initialized in preparation for list execution.
@@ -107,7 +110,7 @@ type PackagePublic struct {
 	Deps      []string          `json:",omitempty"` // all (recursively) imported dependencies
 
 	// Error information
-	Incomplete bool            `json:",omitempty"` // was there an error loading this package or dependencies?
+	// Incomplete is above, packed into the other bools
 	Error      *PackageError   `json:",omitempty"` // error loading this package (not dependencies)
 	DepsErrors []*PackageError `json:",omitempty"` // errors loading dependencies
 
@@ -374,15 +377,17 @@ func ClearPackageCachePartial(args []string) {
 	}
 }
 
-// reloadPackage is like loadPackage but makes sure
+// ReloadPackageNoFlags is like LoadPackageNoFlags but makes sure
 // not to use the package cache.
-func ReloadPackage(arg string, stk *ImportStack) *Package {
+// It is only for use by GOPATH-based "go get".
+// TODO(rsc): When GOPATH-based "go get" is removed, delete this function.
+func ReloadPackageNoFlags(arg string, stk *ImportStack) *Package {
 	p := packageCache[arg]
 	if p != nil {
 		delete(packageCache, p.Dir)
 		delete(packageCache, p.ImportPath)
 	}
-	return LoadPackage(arg, stk)
+	return LoadPackageNoFlags(arg, stk)
 }
 
 // dirToImportPath returns the pseudo-import path we use for a package
@@ -431,6 +436,9 @@ const (
 // but possibly a local import path (an absolute file system path or one beginning
 // with ./ or ../). A local relative path is interpreted relative to srcDir.
 // It returns a *Package describing the package found in that directory.
+// LoadImport does not set tool flags and should only be used by
+// this package, as part of a bigger load operation, and by GOPATH-based "go get".
+// TODO(rsc): When GOPATH-based "go get" is removed, unexport this function.
 func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPos []token.Position, mode int) *Package {
 	stk.Push(path)
 	defer stk.Pop()
@@ -560,11 +568,11 @@ func LoadImport(path, srcDir string, parent *Package, stk *ImportStack, importPo
 	}
 
 	// Checked on every import because the rules depend on the code doing the importing.
-	if perr := disallowInternal(srcDir, parentPath, p, stk); perr != p {
+	if perr := disallowInternal(srcDir, parent, parentPath, p, stk); perr != p {
 		return setErrorPos(perr, importPos)
 	}
 	if mode&ResolveImport != 0 {
-		if perr := disallowVendor(srcDir, parentPath, origPath, p, stk); perr != p {
+		if perr := disallowVendor(srcDir, parent, parentPath, origPath, p, stk); perr != p {
 			return setErrorPos(perr, importPos)
 		}
 	}
@@ -925,7 +933,7 @@ func reusePackage(p *Package, stk *ImportStack) *Package {
 // is allowed to import p.
 // If the import is allowed, disallowInternal returns the original package p.
 // If not, it returns a new package containing just an appropriate error.
-func disallowInternal(srcDir, importerPath string, p *Package, stk *ImportStack) *Package {
+func disallowInternal(srcDir string, importer *Package, importerPath string, p *Package, stk *ImportStack) *Package {
 	// golang.org/s/go14internal:
 	// An import of a path containing the element “internal”
 	// is disallowed if the importing code is outside the tree
@@ -983,10 +991,16 @@ func disallowInternal(srcDir, importerPath string, p *Package, stk *ImportStack)
 			return p
 		}
 	} else {
-		// p is in a module, so make it available based on the import path instead
+		// p is in a module, so make it available based on the importer's import path instead
 		// of the file path (https://golang.org/issue/23970).
-		parent := p.ImportPath[:i]
-		if str.HasPathPrefix(importerPath, parent) {
+		if importerPath == "." {
+			// The importer is a list of command-line files.
+			// Pretend that the import path is the import path of the
+			// directory containing them.
+			importerPath = ModDirImportPath(importer.Dir)
+		}
+		parentOfInternal := p.ImportPath[:i]
+		if str.HasPathPrefix(importerPath, parentOfInternal) {
 			return p
 		}
 	}
@@ -1024,7 +1038,7 @@ func findInternal(path string) (index int, ok bool) {
 // is allowed to import p as path.
 // If the import is allowed, disallowVendor returns the original package p.
 // If not, it returns a new package containing just an appropriate error.
-func disallowVendor(srcDir, importerPath, path string, p *Package, stk *ImportStack) *Package {
+func disallowVendor(srcDir string, importer *Package, importerPath, path string, p *Package, stk *ImportStack) *Package {
 	// The stack includes p.ImportPath.
 	// If that's the only thing on the stack, we started
 	// with a name given on the command line, not an
@@ -1033,26 +1047,18 @@ func disallowVendor(srcDir, importerPath, path string, p *Package, stk *ImportSt
 		return p
 	}
 
-	if p.Standard && ModPackageModuleInfo != nil && importerPath != "" {
-		// Modules must not import vendor packages in the standard library,
-		// but the usual vendor visibility check will not catch them
-		// because the module loader presents them with an ImportPath starting
-		// with "golang_org/" instead of "vendor/".
-		if mod := ModPackageModuleInfo(importerPath); mod != nil {
-			dir := p.Dir
-			if relDir, err := filepath.Rel(p.Root, p.Dir); err == nil {
-				dir = relDir
-			}
-			if _, ok := FindVendor(filepath.ToSlash(dir)); ok {
-				perr := *p
-				perr.Error = &PackageError{
-					ImportStack: stk.Copy(),
-					Err:         "use of vendored package " + path + " not allowed",
-				}
-				perr.Incomplete = true
-				return &perr
-			}
+	// Modules must not import vendor packages in the standard library,
+	// but the usual vendor visibility check will not catch them
+	// because the module loader presents them with an ImportPath starting
+	// with "golang_org/" instead of "vendor/".
+	if p.Standard && !importer.Standard && strings.HasPrefix(p.ImportPath, "golang_org") {
+		perr := *p
+		perr.Error = &PackageError{
+			ImportStack: stk.Copy(),
+			Err:         "use of vendored package " + path + " not allowed",
 		}
+		perr.Incomplete = true
+		return &perr
 	}
 
 	if perr := disallowVendorVisibility(srcDir, p, stk); perr != p {
@@ -1185,27 +1191,6 @@ var foldPath = make(map[string]string)
 func (p *Package) load(stk *ImportStack, bp *build.Package, err error) {
 	p.copyBuild(bp)
 
-	// Decide whether p was listed on the command line.
-	// Given that load is called while processing the command line,
-	// you might think we could simply pass a flag down into load
-	// saying whether we are loading something named on the command
-	// line or something to satisfy an import. But the first load of a
-	// package named on the command line may be as a dependency
-	// of an earlier package named on the command line, not when we
-	// get to that package during command line processing.
-	// For example "go test fmt reflect" will load reflect as a dependency
-	// of fmt before it attempts to load as a command-line argument.
-	// Because loads are cached, the later load will be a no-op,
-	// so it is important that the first load can fill in CmdlinePkg correctly.
-	// Hence the call to a separate matching check here.
-	p.Internal.CmdlinePkg = isCmdlinePkg(p)
-	p.Internal.CmdlinePkgLiteral = isCmdlinePkgLiteral(p)
-
-	p.Internal.Asmflags = BuildAsmflags.For(p)
-	p.Internal.Gcflags = BuildGcflags.For(p)
-	p.Internal.Ldflags = BuildLdflags.For(p)
-	p.Internal.Gccgoflags = BuildGccgoflags.For(p)
-
 	// The localPrefix is the path we interpret ./ imports relative to.
 	// Synthesized main packages sometimes override this.
 	if p.Internal.Local {
@@ -1740,11 +1725,31 @@ func ClearCmdCache() {
 	}
 }
 
+// LoadPackage loads the package named by arg.
+func LoadPackage(arg string, stk *ImportStack) *Package {
+	p := loadPackage(arg, stk)
+	setToolFlags(p)
+	return p
+}
+
+// LoadPackageNoFlags is like LoadPackage
+// but does not guarantee that the build tool flags are set in the result.
+// It is only for use by GOPATH-based "go get"
+// and is only appropriate for preliminary loading of packages.
+// A real load using LoadPackage or (more likely)
+// Packages, PackageAndErrors, or PackagesForBuild
+// must be done before passing the package to any build
+// steps, so that the tool flags can be set properly.
+// TODO(rsc): When GOPATH-based "go get" is removed, delete this function.
+func LoadPackageNoFlags(arg string, stk *ImportStack) *Package {
+	return loadPackage(arg, stk)
+}
+
 // loadPackage is like loadImport but is used for command-line arguments,
 // not for paths found in import statements. In addition to ordinary import paths,
 // loadPackage accepts pseudo-paths beginning with cmd/ to denote commands
 // in the Go command directory, as well as paths to those directories.
-func LoadPackage(arg string, stk *ImportStack) *Package {
+func loadPackage(arg string, stk *ImportStack) *Package {
 	if build.IsLocalImport(arg) {
 		dir := arg
 		if !filepath.IsAbs(dir) {
@@ -1829,54 +1834,64 @@ func Packages(args []string) []*Package {
 // *Package for every argument, even the ones that
 // cannot be loaded at all.
 // The packages that fail to load will have p.Error != nil.
-func PackagesAndErrors(args []string) []*Package {
-	if len(args) > 0 && strings.HasSuffix(args[0], ".go") {
-		return []*Package{GoFilesPackage(args)}
+func PackagesAndErrors(patterns []string) []*Package {
+	if len(patterns) > 0 && strings.HasSuffix(patterns[0], ".go") {
+		return []*Package{GoFilesPackage(patterns)}
 	}
 
-	args = ImportPaths(args)
+	matches := ImportPaths(patterns)
 	var (
 		pkgs    []*Package
 		stk     ImportStack
-		seenArg = make(map[string]bool)
 		seenPkg = make(map[*Package]bool)
 	)
 
-	for _, arg := range args {
-		if seenArg[arg] {
-			continue
-		}
-		seenArg[arg] = true
-		pkg := LoadPackage(arg, &stk)
-		if seenPkg[pkg] {
-			continue
+	for _, m := range matches {
+		for _, pkg := range m.Pkgs {
+			p := loadPackage(pkg, &stk)
+			p.Match = append(p.Match, m.Pattern)
+			p.Internal.CmdlinePkg = true
+			if m.Literal {
+				// Note: do not set = m.Literal unconditionally
+				// because maybe we'll see p matching both
+				// a literal and also a non-literal pattern.
+				p.Internal.CmdlinePkgLiteral = true
+			}
+			if seenPkg[p] {
+				continue
+			}
+			seenPkg[p] = true
+			pkgs = append(pkgs, p)
 		}
-		seenPkg[pkg] = true
-		pkgs = append(pkgs, pkg)
 	}
 
+	// Now that CmdlinePkg is set correctly,
+	// compute the effective flags for all loaded packages
+	// (not just the ones matching the patterns but also
+	// their dependencies).
+	setToolFlags(pkgs...)
+
 	return pkgs
 }
 
-func ImportPaths(args []string) []string {
-	if cmdlineMatchers == nil {
-		SetCmdlinePatterns(search.CleanImportPaths(args))
+func setToolFlags(pkgs ...*Package) {
+	for _, p := range PackageList(pkgs) {
+		p.Internal.Asmflags = BuildAsmflags.For(p)
+		p.Internal.Gcflags = BuildGcflags.For(p)
+		p.Internal.Ldflags = BuildLdflags.For(p)
+		p.Internal.Gccgoflags = BuildGccgoflags.For(p)
 	}
+}
+
+func ImportPaths(args []string) []*search.Match {
 	if ModInit(); cfg.ModulesEnabled {
 		return ModImportPaths(args)
 	}
 	return search.ImportPaths(args)
 }
 
-func ImportPathsForGoGet(args []string) []string {
-	if cmdlineMatchers == nil {
-		SetCmdlinePatterns(search.CleanImportPaths(args))
-	}
-	return search.ImportPathsNoDotExpansion(args)
-}
-
-// packagesForBuild is like 'packages' but fails if any of
-// the packages or their dependencies have errors
+// PackagesForBuild is like Packages but exits
+// if any of the packages or their dependencies have errors
 // (cannot be built).
 func PackagesForBuild(args []string) []*Package {
 	pkgs := PackagesAndErrors(args)
@@ -1924,7 +1939,6 @@ func PackagesForBuild(args []string) []*Package {
 func GoFilesPackage(gofiles []string) *Package {
 	ModInit()
 
-	// TODO: Remove this restriction.
 	for _, f := range gofiles {
 		if !strings.HasSuffix(f, ".go") {
 			base.Fatalf("named files must be .go files")
@@ -1976,6 +1990,11 @@ func GoFilesPackage(gofiles []string) *Package {
 	}
 
 	bp, err := ctxt.ImportDir(dir, 0)
+	if ModDirImportPath != nil {
+		// Use the effective import path of the directory
+		// for deciding visibility during pkg.load.
+		bp.ImportPath = ModDirImportPath(dir)
+	}
 	pkg := new(Package)
 	pkg.Internal.Local = true
 	pkg.Internal.CmdlineFiles = true
@@ -1985,6 +2004,7 @@ func GoFilesPackage(gofiles []string) *Package {
 	pkg.Internal.LocalPrefix = dirToImportPath(dir)
 	pkg.ImportPath = "command-line-arguments"
 	pkg.Target = ""
+	pkg.Match = gofiles
 
 	if pkg.Name == "main" {
 		_, elem := filepath.Split(gofiles[0])
@@ -1999,5 +2019,7 @@ func GoFilesPackage(gofiles []string) *Package {
 		}
 	}
 
+	setToolFlags(pkg)
+
 	return pkg
 }
diff --git a/src/cmd/go/internal/load/search.go b/src/cmd/go/internal/load/search.go
index d379c7b021..cf09c7b0a8 100644
--- a/src/cmd/go/internal/load/search.go
+++ b/src/cmd/go/internal/load/search.go
@@ -6,7 +6,6 @@ package load
 
 import (
 	"path/filepath"
-	"runtime"
 	"strings"
 
 	"cmd/go/internal/search"
@@ -28,13 +27,7 @@ func MatchPackage(pattern, cwd string) func(*Package) bool {
 		}
 		dir = filepath.Join(cwd, dir)
 		if pattern == "" {
-			return func(p *Package) bool {
-				// TODO(rsc): This is wrong. See golang.org/issue/25878.
-				if runtime.GOOS != "windows" {
-					return p.Dir == dir
-				}
-				return strings.EqualFold(p.Dir, dir)
-			}
+			return func(p *Package) bool { return p.Dir == dir }
 		}
 		matchPath := search.MatchPattern(pattern)
 		return func(p *Package) bool {
diff --git a/src/cmd/go/internal/modcmd/download.go b/src/cmd/go/internal/modcmd/download.go
index 0a457a56f2..2f072d73cf 100644
--- a/src/cmd/go/internal/modcmd/download.go
+++ b/src/cmd/go/internal/modcmd/download.go
@@ -41,7 +41,7 @@ corresponding to this Go struct:
         Dir     string // absolute path to cached source root directory
     }
 
-See 'go help module' for more about module queries.
+See 'go help modules' for more about module queries.
 	`,
 }
 
diff --git a/src/cmd/go/internal/modcmd/fix.go b/src/cmd/go/internal/modcmd/fix.go
deleted file mode 100644
index bfb51456a6..0000000000
--- a/src/cmd/go/internal/modcmd/fix.go
+++ /dev/null
@@ -1,65 +0,0 @@
-// Copyright 2018 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// go mod fix
-
-package modcmd
-
-import (
-	"cmd/go/internal/base"
-	"cmd/go/internal/modload"
-)
-
-var cmdFix = &base.Command{
-	UsageLine: "go mod fix",
-	Short:     "make go.mod semantically consistent",
-	Long: `
-Fix updates go.mod to use canonical version identifiers and
-to be semantically consistent. For example, consider this go.mod file:
-
-	module M
-
-	require (
-		A v1
-		B v1.0.0
-		C v1.0.0
-		D v1.2.3
-		E dev
-	)
-
-	exclude D v1.2.3
-
-First, fix rewrites non-canonical version identifiers to semver form, so
-A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the latest
-commit on the dev branch, perhaps v0.0.0-20180523231146-b3f5c0f6e5f1.
-
-Next, fix updates requirements to respect exclusions, so the requirement
-on the excluded D v1.2.3 is updated to use the next available version of D,
-perhaps D v1.2.4 or D v1.3.0.
-
-Finally, fix removes redundant or misleading requirements.
-For example, if A v1.0.0 itself requires B v1.2.0 and C v1.0.0, then go.mod's
-requirement of B v1.0.0 is misleading (superseded by A's need for v1.2.0),
-and its requirement of C v1.0.0 is redundant (implied by A's need for the
-same version), so both will be removed. If module M contains packages
-that directly import packages from B or C, then the requirements will be
-kept but updated to the actual versions being used.
-
-Although fix runs the fix-up operation in isolation, the fix-up also
-runs automatically any time a go command uses the module graph,
-to update go.mod to reflect reality. Because the module graph defines
-the meaning of import statements, any commands that load packages
-also use and therefore fix the module graph. For example,
-go build, go get, go install, go list, go test, go mod graph, go mod tidy,
-and other commands all effectively imply go mod fix.
-	`,
-	Run: runFix,
-}
-
-func runFix(cmd *base.Command, args []string) {
-	if len(args) != 0 {
-		base.Fatalf("go mod fix: fix takes no arguments")
-	}
-	modload.LoadBuildList() // writes go.mod
-}
diff --git a/src/cmd/go/internal/modcmd/mod.go b/src/cmd/go/internal/modcmd/mod.go
index c1d0c13a10..f150cc9728 100644
--- a/src/cmd/go/internal/modcmd/mod.go
+++ b/src/cmd/go/internal/modcmd/mod.go
@@ -21,7 +21,6 @@ See 'go help modules' for an overview of module functionality.
 	Commands: []*base.Command{
 		cmdDownload,
 		cmdEdit,
-		cmdFix,
 		cmdGraph,
 		cmdInit,
 		cmdTidy,
diff --git a/src/cmd/go/internal/modcmd/tidy.go b/src/cmd/go/internal/modcmd/tidy.go
index 54f47e764f..f2063a9ea6 100644
--- a/src/cmd/go/internal/modcmd/tidy.go
+++ b/src/cmd/go/internal/modcmd/tidy.go
@@ -44,10 +44,11 @@ func runTidy(cmd *base.Command, args []string) {
 
 	// LoadALL adds missing modules.
 	// Remove unused modules.
-	used := map[module.Version]bool{modload.Target: true}
+	used := make(map[module.Version]bool)
 	for _, pkg := range modload.LoadALL() {
 		used[modload.PackageModule(pkg)] = true
 	}
+	used[modload.Target] = true // note: LoadALL initializes Target
 
 	inGoMod := make(map[string]bool)
 	for _, r := range modload.ModFile().Require {
diff --git a/src/cmd/go/internal/modcmd/why.go b/src/cmd/go/internal/modcmd/why.go
index 6923685599..03e0a039bc 100644
--- a/src/cmd/go/internal/modcmd/why.go
+++ b/src/cmd/go/internal/modcmd/why.go
@@ -100,20 +100,22 @@ func runWhy(cmd *base.Command, args []string) {
 			sep = "\n"
 		}
 	} else {
-		pkgs := modload.ImportPaths(args) // resolve to packages
-		loadALL()                         // rebuild graph, from main module (not from named packages)
+		matches := modload.ImportPaths(args) // resolve to packages
+		loadALL()                            // rebuild graph, from main module (not from named packages)
 		sep := ""
-		for _, path := range pkgs {
-			why := modload.Why(path)
-			if why == "" {
-				vendoring := ""
-				if *whyVendor {
-					vendoring = " to vendor"
+		for _, m := range matches {
+			for _, path := range m.Pkgs {
+				why := modload.Why(path)
+				if why == "" {
+					vendoring := ""
+					if *whyVendor {
+						vendoring = " to vendor"
+					}
+					why = "(main module does not need" + vendoring + " package " + path + ")\n"
 				}
-				why = "(main module does not need" + vendoring + " package " + path + ")\n"
+				fmt.Printf("%s# %s\n%s", sep, path, why)
+				sep = "\n"
 			}
-			fmt.Printf("%s# %s\n%s", sep, path, why)
-			sep = "\n"
 		}
 	}
 }
diff --git a/src/cmd/go/internal/modconv/convert_test.go b/src/cmd/go/internal/modconv/convert_test.go
index f430380871..ad27abb8ef 100644
--- a/src/cmd/go/internal/modconv/convert_test.go
+++ b/src/cmd/go/internal/modconv/convert_test.go
@@ -61,28 +61,36 @@ func TestConvertLegacyConfig(t *testing.T) {
 		vers  string
 		gomod string
 	}{
-		{
-			// Gopkg.lock parsing.
-			"github.com/golang/dep", "v0.4.0",
-			`module github.com/golang/dep
-
-			require (
-				github.com/Masterminds/semver v0.0.0-20170726230514-a93e51b5a57e
-				github.com/Masterminds/vcs v1.11.1
-				github.com/armon/go-radix v0.0.0-20160115234725-4239b77079c7
-				github.com/boltdb/bolt v1.3.1
-				github.com/go-yaml/yaml v0.0.0-20170407172122-cd8b52f8269e
-				github.com/golang/protobuf v0.0.0-20170901042739-5afd06f9d81a
-				github.com/jmank88/nuts v0.3.0
-				github.com/nightlyone/lockfile v0.0.0-20170707060451-e83dc5e7bba0
-				github.com/pelletier/go-toml v0.0.0-20171218135716-b8b5e7696574
-				github.com/pkg/errors v0.8.0
-				github.com/sdboyer/constext v0.0.0-20170321163424-836a14457353
-				golang.org/x/net v0.0.0-20170828231752-66aacef3dd8a
-				golang.org/x/sync v0.0.0-20170517211232-f52d1811a629
-				golang.org/x/sys v0.0.0-20170830134202-bb24a47a89ea
-			)`,
-		},
+		/*
+			Different versions of git seem to find or not find
+			github.com/Masterminds/semver's a93e51b5a57e,
+			which is an unmerged pull request.
+			We'd rather not provide access to unmerged pull requests,
+			so the line is removed from the golden file here,
+			but some git commands still find it somehow.
+
+			{
+				// Gopkg.lock parsing.
+				"github.com/golang/dep", "v0.4.0",
+				`module github.com/golang/dep
+
+				require (
+					github.com/Masterminds/vcs v1.11.1
+					github.com/armon/go-radix v0.0.0-20160115234725-4239b77079c7
+					github.com/boltdb/bolt v1.3.1
+					github.com/go-yaml/yaml v0.0.0-20170407172122-cd8b52f8269e
+					github.com/golang/protobuf v0.0.0-20170901042739-5afd06f9d81a
+					github.com/jmank88/nuts v0.3.0
+					github.com/nightlyone/lockfile v0.0.0-20170707060451-e83dc5e7bba0
+					github.com/pelletier/go-toml v0.0.0-20171218135716-b8b5e7696574
+					github.com/pkg/errors v0.8.0
+					github.com/sdboyer/constext v0.0.0-20170321163424-836a14457353
+					golang.org/x/net v0.0.0-20170828231752-66aacef3dd8a
+					golang.org/x/sync v0.0.0-20170517211232-f52d1811a629
+					golang.org/x/sys v0.0.0-20170830134202-bb24a47a89ea
+				)`,
+			},
+		*/
 
 		// TODO: https://github.com/docker/distribution uses vendor.conf
 
diff --git a/src/cmd/go/internal/modfetch/codehost/vcs.go b/src/cmd/go/internal/modfetch/codehost/vcs.go
index 03def8e082..9e862a0ef8 100644
--- a/src/cmd/go/internal/modfetch/codehost/vcs.go
+++ b/src/cmd/go/internal/modfetch/codehost/vcs.go
@@ -22,6 +22,17 @@ import (
 	"cmd/go/internal/str"
 )
 
+// A VCSError indicates an error using a version control system.
+// The implication of a VCSError is that we know definitively where
+// to get the code, but we can't access it due to the error.
+// The caller should report this error instead of continuing to probe
+// other possible module paths.
+type VCSError struct {
+	Err error
+}
+
+func (e *VCSError) Error() string { return e.Err.Error() }
+
 func NewRepo(vcs, remote string) (Repo, error) {
 	type key struct {
 		vcs    string
@@ -33,6 +44,9 @@ func NewRepo(vcs, remote string) (Repo, error) {
 	}
 	c := vcsRepoCache.Do(key{vcs, remote}, func() interface{} {
 		repo, err := newVCSRepo(vcs, remote)
+		if err != nil {
+			err = &VCSError{err}
+		}
 		return cached{repo, err}
 	}).(cached)
 
diff --git a/src/cmd/go/internal/modfetch/coderepo_test.go b/src/cmd/go/internal/modfetch/coderepo_test.go
index c46705105d..79b82786cb 100644
--- a/src/cmd/go/internal/modfetch/coderepo_test.go
+++ b/src/cmd/go/internal/modfetch/coderepo_test.go
@@ -228,10 +228,9 @@ var codeRepoTests = []struct {
 		path:    "swtch.com/testmod",
 		rev:     "v1.0.0",
 		version: "v1.0.0",
-		name:    "v1.0.0",
-		short:   "v1.0.0",
-		time:    time.Date(1972, 7, 18, 12, 34, 56, 0, time.UTC),
-		gomod:   "module \"swtch.com/testmod\"\n",
+		// NO name or short - we intentionally ignore those in the proxy protocol
+		time:  time.Date(1972, 7, 18, 12, 34, 56, 0, time.UTC),
+		gomod: "module \"swtch.com/testmod\"\n",
 	},
 	{
 		// redirect to googlesource
diff --git a/src/cmd/go/internal/modfetch/repo.go b/src/cmd/go/internal/modfetch/repo.go
index 003479461c..0ea8c1f0e3 100644
--- a/src/cmd/go/internal/modfetch/repo.go
+++ b/src/cmd/go/internal/modfetch/repo.go
@@ -216,7 +216,11 @@ func lookup(path string) (r Repo, err error) {
 		return lookupProxy(path)
 	}
 
-	rr, err := get.RepoRootForImportPath(path, get.PreferMod, web.Secure)
+	security := web.Secure
+	if get.Insecure {
+		security = web.Insecure
+	}
+	rr, err := get.RepoRootForImportPath(path, get.PreferMod, security)
 	if err != nil {
 		// We don't know where to find code for a module with this path.
 		return nil, err
@@ -237,6 +241,9 @@ func lookup(path string) (r Repo, err error) {
 func lookupCodeRepo(rr *get.RepoRoot) (codehost.Repo, error) {
 	code, err := codehost.NewRepo(rr.VCS, rr.Repo)
 	if err != nil {
+		if _, ok := err.(*codehost.VCSError); ok {
+			return nil, err
+		}
 		return nil, fmt.Errorf("lookup %s: %v", rr.Root, err)
 	}
 	return code, nil
@@ -254,7 +261,11 @@ func ImportRepoRev(path, rev string) (Repo, *RevInfo, error) {
 	// Note: Because we are converting a code reference from a legacy
 	// version control system, we ignore meta tags about modules
 	// and use only direct source control entries (get.IgnoreMod).
-	rr, err := get.RepoRootForImportPath(path, get.IgnoreMod, web.Secure)
+	security := web.Secure
+	if get.Insecure {
+		security = web.Insecure
+	}
+	rr, err := get.RepoRootForImportPath(path, get.IgnoreMod, security)
 	if err != nil {
 		return nil, nil, err
 	}
diff --git a/src/cmd/go/internal/modfile/rule.go b/src/cmd/go/internal/modfile/rule.go
index f669575c86..e11f0a6e31 100644
--- a/src/cmd/go/internal/modfile/rule.go
+++ b/src/cmd/go/internal/modfile/rule.go
@@ -250,7 +250,7 @@ func (f *File) add(errs *bytes.Buffer, line *Line, verb string, args []string, f
 			arrow = 1
 		}
 		if len(args) < arrow+2 || len(args) > arrow+3 || args[arrow] != "=>" {
-			fmt.Fprintf(errs, "%s:%d: usage: %s module/path [v1.2.3] => other/module v1.4\n\t or %s module/path [v1.2.3] => ../local/directory", f.Syntax.Name, line.Start.Line, verb, verb)
+			fmt.Fprintf(errs, "%s:%d: usage: %s module/path [v1.2.3] => other/module v1.4\n\t or %s module/path [v1.2.3] => ../local/directory\n", f.Syntax.Name, line.Start.Line, verb, verb)
 			return
 		}
 		s, err := parseString(&args[0])
@@ -287,11 +287,11 @@ func (f *File) add(errs *bytes.Buffer, line *Line, verb string, args []string, f
 		nv := ""
 		if len(args) == arrow+2 {
 			if !IsDirectoryPath(ns) {
-				fmt.Fprintf(errs, "%s:%d: replacement module without version must be directory path (rooted or starting with ./ or ../)", f.Syntax.Name, line.Start.Line)
+				fmt.Fprintf(errs, "%s:%d: replacement module without version must be directory path (rooted or starting with ./ or ../)\n", f.Syntax.Name, line.Start.Line)
 				return
 			}
 			if filepath.Separator == '/' && strings.Contains(ns, `\`) {
-				fmt.Fprintf(errs, "%s:%d: replacement directory appears to be Windows path (on a non-windows system)", f.Syntax.Name, line.Start.Line)
+				fmt.Fprintf(errs, "%s:%d: replacement directory appears to be Windows path (on a non-windows system)\n", f.Syntax.Name, line.Start.Line)
 				return
 			}
 		}
@@ -303,7 +303,7 @@ func (f *File) add(errs *bytes.Buffer, line *Line, verb string, args []string, f
 				return
 			}
 			if IsDirectoryPath(ns) {
-				fmt.Fprintf(errs, "%s:%d: replacement module directory path %q cannot have version", f.Syntax.Name, line.Start.Line, ns)
+				fmt.Fprintf(errs, "%s:%d: replacement module directory path %q cannot have version\n", f.Syntax.Name, line.Start.Line, ns)
 				return
 			}
 		}
diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index f4a92686a5..90a5bd8130 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -229,7 +229,7 @@ func runGet(cmd *base.Command, args []string) {
 	// and a list of install targets (for the "go install" at the end).
 	var tasks []*task
 	var install []string
-	for _, arg := range search.CleanImportPaths(args) {
+	for _, arg := range search.CleanPatterns(args) {
 		// Argument is module query path@vers, or else path with implicit @latest.
 		path := arg
 		vers := ""
@@ -519,8 +519,9 @@ func runGet(cmd *base.Command, args []string) {
 		// Note that 'go get -u' without any arguments results in len(install) == 1:
 		// search.CleanImportPaths returns "." for empty args.
 		work.BuildInit()
-		var pkgs []string
-		for _, p := range load.PackagesAndErrors(install) {
+		pkgs := load.PackagesAndErrors(install)
+		var todo []*load.Package
+		for _, p := range pkgs {
 			// Ignore "no Go source files" errors for 'go get' operations on modules.
 			if p.Error != nil {
 				if len(args) == 0 && getU != "" && strings.HasPrefix(p.Error.Err, "no Go files") {
@@ -534,14 +535,14 @@ func runGet(cmd *base.Command, args []string) {
 					continue
 				}
 			}
-			pkgs = append(pkgs, p.ImportPath)
+			todo = append(todo, p)
 		}
 
 		// If -d was specified, we're done after the download: no build.
 		// (The load.PackagesAndErrors is what did the download
 		// of the named packages and their dependencies.)
-		if len(pkgs) > 0 && !*getD {
-			work.InstallPackages(pkgs)
+		if len(todo) > 0 && !*getD {
+			work.InstallPackages(install, todo)
 		}
 	}
 }
diff --git a/src/cmd/go/internal/modload/help.go b/src/cmd/go/internal/modload/help.go
index 64c70b7d7b..9a12b24482 100644
--- a/src/cmd/go/internal/modload/help.go
+++ b/src/cmd/go/internal/modload/help.go
@@ -6,8 +6,7 @@ package modload
 
 import "cmd/go/internal/base"
 
-// TODO(rsc): The links out to research.swtch.com here should all be
-// replaced eventually with links to proper documentation.
+// TODO(rsc): The "module code layout" section needs to be written.
 
 var HelpModules = &base.Command{
 	UsageLine: "modules",
@@ -81,7 +80,7 @@ depends on specific versions of golang.org/x/text and gopkg.in/yaml.v2:
 The go.mod file can also specify replacements and excluded versions
 that only apply when building the module directly; they are ignored
 when the module is incorporated into a larger build.
-For more about the go.mod file, see https://research.swtch.com/vgo-module.
+For more about the go.mod file, see 'go help go.mod'.
 
 To start a new module, simply create a go.mod file in the root of the
 module's directory tree, containing only a module statement.
@@ -336,8 +335,6 @@ For now, see https://research.swtch.com/vgo-module for information
 about how source code in version control systems is mapped to
 module file trees.
 
-TODO: Add documentation to go command.
-
 Module downloading and verification
 
 The go command maintains, in the main module's root directory alongside
@@ -381,3 +378,73 @@ top-level vendor directory is used; vendor directories in other locations
 are still ignored.
 	`,
 }
+
+var HelpGoMod = &base.Command{
+	UsageLine: "go.mod",
+	Short:     "the go.mod file",
+	Long: `
+A module version is defined by a tree of source files, with a go.mod
+file in its root. When the go command is run, it looks in the current
+directory and then successive parent directories to find the go.mod
+marking the root of the main (current) module.
+
+The go.mod file itself is line-oriented, with // comments but
+no /* */ comments. Each line holds a single directive, made up of a
+verb followed by arguments. For example:
+
+	module my/thing
+	require other/thing v1.0.2
+	require new/thing v2.3.4
+	exclude old/thing v1.2.3
+	replace bad/thing v1.4.5 => good/thing v1.4.5
+
+The verbs are module, to define the module path; require, to require
+a particular module at a given version or later; exclude, to exclude
+a particular module version from use; and replace, to replace a module
+version with a different module version. Exclude and replace apply only
+in the main module's go.mod and are ignored in dependencies.
+See https://research.swtch.com/vgo-mvs for details.
+
+The leading verb can be factored out of adjacent lines to create a block,
+like in Go imports:
+
+	require (
+		new/thing v2.3.4
+		old/thing v1.2.3
+	)
+
+The go.mod file is designed both to be edited directly and to be
+easily updated by tools. The 'go mod edit' command can be used to
+parse and edit the go.mod file from programs and tools.
+See 'go help mod edit'.
+
+The go command automatically updates go.mod each time it uses the
+module graph, to make sure go.mod always accurately reflects reality
+and is properly formatted.
+
+The update rewrites non-canonical version identifiers to semver form,
+so A's v1 becomes v1.0.0 and E's dev becomes the pseudo-version for the
+latest commit on the dev branch, perhaps v0.0.0-20180523231146-b3f5c0f6e5f1.
+
+The update modifies requirements to respect exclusions, so the
+requirement on the excluded D v1.2.3 is updated to use the next
+available version of D, perhaps D v1.2.4 or D v1.3.0.
+
+The update removes redundant or misleading requirements.
+For example, if A v1.0.0 itself requires B v1.2.0 and C v1.0.0,
+then go.mod's requirement of B v1.0.0 is misleading (superseded by
+A's need for v1.2.0), and its requirement of C v1.0.0 is redundant
+(implied by A's need for the same version), so both will be removed.
+If module M contains packages that directly import packages from B or
+C, then the requirements will be kept but updated to the actual
+versions being used.
+
+Finally, the update reformats the go.mod in a canonical formatting, so
+that future mechanical changes will result in minimal diffs.
+
+Because the module graph defines the meaning of import statements, any
+commands that load packages also use and therefore update go.mod,
+including go build, go get, go install, go list, go test, go mod graph,
+go mod tidy, and go mod why.
+	`,
+}
diff --git a/src/cmd/go/internal/modload/import.go b/src/cmd/go/internal/modload/import.go
index 3b954f18fe..78ae83e4bf 100644
--- a/src/cmd/go/internal/modload/import.go
+++ b/src/cmd/go/internal/modload/import.go
@@ -14,6 +14,7 @@ import (
 	"strings"
 
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/modfetch/codehost"
 	"cmd/go/internal/module"
 	"cmd/go/internal/par"
 	"cmd/go/internal/search"
@@ -133,6 +134,9 @@ func Import(path string) (m module.Version, dir string, err error) {
 
 	m, _, err = QueryPackage(path, "latest", Allowed)
 	if err != nil {
+		if _, ok := err.(*codehost.VCSError); ok {
+			return module.Version{}, "", err
+		}
 		return module.Version{}, "", &ImportMissingError{ImportPath: path}
 	}
 	return m, "", &ImportMissingError{ImportPath: path, Module: m}
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 5e9db0f9ea..f995bad13b 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -150,8 +150,20 @@ func Init() {
 		ModRoot = cwd
 	} else {
 		ModRoot, _ = FindModuleRoot(cwd, "", MustUseModules)
-		if ModRoot == "" && !MustUseModules {
-			return
+		if !MustUseModules {
+			if ModRoot == "" {
+				return
+			}
+			if search.InDir(ModRoot, os.TempDir()) == "." {
+				// If you create /tmp/go.mod for experimenting,
+				// then any tests that create work directories under /tmp
+				// will find it and get modules when they're not expecting them.
+				// It's a bit of a peculiar thing to disallow but quite mysterious
+				// when it happens. See golang.org/issue/26708.
+				ModRoot = ""
+				fmt.Fprintf(os.Stderr, "go: warning: ignoring go.mod in system temp root %v\n", os.TempDir())
+				return
+			}
 		}
 	}
 
@@ -163,6 +175,7 @@ func Init() {
 	load.ModPackageBuildInfo = PackageBuildInfo
 	load.ModInfoProg = ModInfoProg
 	load.ModImportFromFiles = ImportFromFiles
+	load.ModDirImportPath = DirImportPath
 
 	search.SetModRoot(ModRoot)
 }
diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 389c643db2..285daa8f4f 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -27,6 +27,7 @@ import (
 	"cmd/go/internal/par"
 	"cmd/go/internal/search"
 	"cmd/go/internal/semver"
+	"cmd/go/internal/str"
 )
 
 // buildList is the list of modules to use for building packages.
@@ -50,24 +51,46 @@ var loaded *loader
 
 // ImportPaths returns the set of packages matching the args (patterns),
 // adding modules to the build list as needed to satisfy new imports.
-func ImportPaths(args []string) []string {
+func ImportPaths(patterns []string) []*search.Match {
 	InitMod()
 
-	cleaned := search.CleanImportPaths(args)
+	var matches []*search.Match
+	for _, pattern := range search.CleanPatterns(patterns) {
+		m := &search.Match{
+			Pattern: pattern,
+			Literal: !strings.Contains(pattern, "...") && !search.IsMetaPackage(pattern),
+		}
+		if m.Literal {
+			m.Pkgs = []string{pattern}
+		}
+		matches = append(matches, m)
+	}
+
+	fsDirs := make([][]string, len(matches))
 	loaded = newLoader()
-	var paths []string
-	loaded.load(func() []string {
-		var roots []string
-		paths = nil
-		for _, pkg := range cleaned {
+	updateMatches := func(iterating bool) {
+		for i, m := range matches {
 			switch {
-			case build.IsLocalImport(pkg) || filepath.IsAbs(pkg):
-				list := []string{pkg}
-				if strings.Contains(pkg, "...") {
-					// TODO: Where is the go.mod cutoff?
-					list = warnPattern(pkg, search.AllPackagesInFS(pkg))
+			case build.IsLocalImport(m.Pattern) || filepath.IsAbs(m.Pattern):
+				// Evaluate list of file system directories on first iteration.
+				if fsDirs[i] == nil {
+					var dirs []string
+					if m.Literal {
+						dirs = []string{m.Pattern}
+					} else {
+						dirs = search.MatchPackagesInFS(m.Pattern).Pkgs
+					}
+					fsDirs[i] = dirs
 				}
-				for _, pkg := range list {
+
+				// Make a copy of the directory list and translate to import paths.
+				// Note that whether a directory corresponds to an import path
+				// changes as the build list is updated, and a directory can change
+				// from not being in the build list to being in it and back as
+				// the exact version of a particular module increases during
+				// the loader iterations.
+				m.Pkgs = str.StringList(fsDirs[i])
+				for i, pkg := range m.Pkgs {
 					dir := pkg
 					if !filepath.IsAbs(dir) {
 						dir = filepath.Join(cwd, pkg)
@@ -93,38 +116,67 @@ func ImportPaths(args []string) []string {
 					} else if path := pathInModuleCache(dir); path != "" {
 						pkg = path
 					} else {
-						base.Errorf("go: directory %s outside available modules", base.ShortPath(dir))
-						continue
+						pkg = ""
+						if !iterating {
+							base.Errorf("go: directory %s outside available modules", base.ShortPath(dir))
+						}
 					}
-					roots = append(roots, pkg)
-					paths = append(paths, pkg)
+					info, err := os.Stat(dir)
+					if err != nil || !info.IsDir() {
+						// If the directory does not exist,
+						// don't turn it into an import path
+						// that will trigger a lookup.
+						pkg = ""
+						if !iterating {
+							if err != nil {
+								base.Errorf("go: no such directory %v", m.Pattern)
+							} else {
+								base.Errorf("go: %s is not a directory", m.Pattern)
+							}
+						}
+					}
+					m.Pkgs[i] = pkg
 				}
 
-			case pkg == "all":
+			case strings.Contains(m.Pattern, "..."):
+				m.Pkgs = matchPackages(m.Pattern, loaded.tags, true, buildList)
+
+			case m.Pattern == "all":
 				loaded.testAll = true
-				// TODO: Don't print warnings multiple times.
-				roots = append(roots, warnPattern("all", matchPackages("...", loaded.tags, false, []module.Version{Target}))...)
-				paths = append(paths, "all") // will expand after load completes
-
-			case search.IsMetaPackage(pkg): // std, cmd
-				list := search.AllPackages(pkg)
-				roots = append(roots, list...)
-				paths = append(paths, list...)
-
-			case strings.Contains(pkg, "..."):
-				// TODO: Don't we need to reevaluate this one last time once the build list stops changing?
-				list := warnPattern(pkg, matchPackages(pkg, loaded.tags, true, buildList))
-				roots = append(roots, list...)
-				paths = append(paths, list...)
-
-			default:
-				roots = append(roots, pkg)
-				paths = append(paths, pkg)
+				if iterating {
+					// Enumerate the packages in the main module.
+					// We'll load the dependencies as we find them.
+					m.Pkgs = matchPackages("...", loaded.tags, false, []module.Version{Target})
+				} else {
+					// Starting with the packages in the main module,
+					// enumerate the full list of "all".
+					m.Pkgs = loaded.computePatternAll(m.Pkgs)
+				}
+
+			case search.IsMetaPackage(m.Pattern): // std, cmd
+				if len(m.Pkgs) == 0 {
+					m.Pkgs = search.MatchPackages(m.Pattern).Pkgs
+				}
+			}
+		}
+	}
+
+	loaded.load(func() []string {
+		var roots []string
+		updateMatches(true)
+		for _, m := range matches {
+			for _, pkg := range m.Pkgs {
+				if pkg != "" {
+					roots = append(roots, pkg)
+				}
 			}
 		}
 		return roots
 	})
 
+	// One last pass to finalize wildcards.
+	updateMatches(false)
+
 	// A given module path may be used as itself or as a replacement for another
 	// module, but not both at the same time. Otherwise, the aliasing behavior is
 	// too subtle (see https://golang.org/issue/26607), and we don't want to
@@ -142,33 +194,10 @@ func ImportPaths(args []string) []string {
 		}
 	}
 	base.ExitIfErrors()
-
 	WriteGoMod()
 
-	// Process paths to produce final paths list.
-	// Remove duplicates and expand "all".
-	have := make(map[string]bool)
-	var final []string
-	for _, path := range paths {
-		if have[path] {
-			continue
-		}
-		have[path] = true
-		if path == "all" {
-			for _, pkg := range loaded.pkgs {
-				if e, ok := pkg.err.(*ImportMissingError); ok && e.Module.Path == "" {
-					continue // Package doesn't actually exist, so don't report it.
-				}
-				if !have[pkg.path] {
-					have[pkg.path] = true
-					final = append(final, pkg.path)
-				}
-			}
-			continue
-		}
-		final = append(final, path)
-	}
-	return final
+	search.WarnUnmatched(matches)
+	return matches
 }
 
 // pathInModuleCache returns the import path of the directory dir,
@@ -219,6 +248,28 @@ func ImportFromFiles(gofiles []string) {
 	WriteGoMod()
 }
 
+// DirImportPath returns the effective import path for dir,
+// provided it is within the main module, or else returns ".".
+func DirImportPath(dir string) string {
+	if !filepath.IsAbs(dir) {
+		dir = filepath.Join(cwd, dir)
+	} else {
+		dir = filepath.Clean(dir)
+	}
+
+	if dir == ModRoot {
+		return Target.Path
+	}
+	if strings.HasPrefix(dir, ModRoot+string(filepath.Separator)) {
+		suffix := filepath.ToSlash(dir[len(ModRoot):])
+		if strings.HasPrefix(suffix, "/vendor/") {
+			return strings.TrimPrefix(suffix, "/vendor/")
+		}
+		return Target.Path + suffix
+	}
+	return "."
+}
+
 // LoadBuildList loads and returns the build list from go.mod.
 // The loading of the build list happens automatically in ImportPaths:
 // LoadBuildList need only be called if ImportPaths is not
@@ -581,6 +632,35 @@ func (ld *loader) doPkg(item interface{}) {
 	}
 }
 
+// computePatternAll returns the list of packages matching pattern "all",
+// starting with a list of the import paths for the packages in the main module.
+func (ld *loader) computePatternAll(paths []string) []string {
+	seen := make(map[*loadPkg]bool)
+	var all []string
+	var walk func(*loadPkg)
+	walk = func(pkg *loadPkg) {
+		if seen[pkg] {
+			return
+		}
+		seen[pkg] = true
+		if pkg.testOf == nil {
+			all = append(all, pkg.path)
+		}
+		for _, p := range pkg.imports {
+			walk(p)
+		}
+		if p := pkg.test; p != nil {
+			walk(p)
+		}
+	}
+	for _, path := range paths {
+		walk(ld.pkg(path, false))
+	}
+	sort.Strings(all)
+
+	return all
+}
+
 // scanDir is like imports.ScanDir but elides known magic imports from the list,
 // so that we do not go looking for packages that don't really exist.
 //
diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index bd3141865c..3b550f1db7 100644
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -6,6 +6,7 @@ package modload
 
 import (
 	"cmd/go/internal/modfetch"
+	"cmd/go/internal/modfetch/codehost"
 	"cmd/go/internal/module"
 	"cmd/go/internal/semver"
 	"fmt"
@@ -223,6 +224,11 @@ func QueryPackage(path, query string, allowed func(module.Version) bool) (module
 	for p := path; p != "."; p = pathpkg.Dir(p) {
 		info, err := Query(p, query, allowed)
 		if err != nil {
+			if _, ok := err.(*codehost.VCSError); ok {
+				// A VCSError means we know where to find the code,
+				// we just can't. Abort search.
+				return module.Version{}, nil, err
+			}
 			if finalErr == errMissing {
 				finalErr = err
 			}
diff --git a/src/cmd/go/internal/search/search.go b/src/cmd/go/internal/search/search.go
index b020f600c1..60ae73696b 100644
--- a/src/cmd/go/internal/search/search.go
+++ b/src/cmd/go/internal/search/search.go
@@ -17,32 +17,22 @@ import (
 	"strings"
 )
 
-// AllPackages returns all the packages that can be found
+// A Match represents the result of matching a single package pattern.
+type Match struct {
+	Pattern string   // the pattern itself
+	Literal bool     // whether it is a literal (no wildcards)
+	Pkgs    []string // matching packages (dirs or import paths)
+}
+
+// MatchPackages returns all the packages that can be found
 // under the $GOPATH directories and $GOROOT matching pattern.
 // The pattern is either "all" (all packages), "std" (standard packages),
 // "cmd" (standard commands), or a path including "...".
-func AllPackages(pattern string) []string {
-	pkgs := MatchPackages(pattern)
-	if len(pkgs) == 0 {
-		fmt.Fprintf(os.Stderr, "warning: %q matched no packages\n", pattern)
-	}
-	return pkgs
-}
-
-// AllPackagesInFS is like allPackages but is passed a pattern
-// beginning ./ or ../, meaning it should scan the tree rooted
-// at the given directory. There are ... in the pattern too.
-func AllPackagesInFS(pattern string) []string {
-	pkgs := MatchPackagesInFS(pattern)
-	if len(pkgs) == 0 {
-		fmt.Fprintf(os.Stderr, "warning: %q matched no packages\n", pattern)
+func MatchPackages(pattern string) *Match {
+	m := &Match{
+		Pattern: pattern,
+		Literal: false,
 	}
-	return pkgs
-}
-
-// MatchPackages returns a list of package paths matching pattern
-// (see go help packages for pattern syntax).
-func MatchPackages(pattern string) []string {
 	match := func(string) bool { return true }
 	treeCanMatch := func(string) bool { return true }
 	if !IsMetaPackage(pattern) {
@@ -56,7 +46,6 @@ func MatchPackages(pattern string) []string {
 	if !cfg.BuildContext.CgoEnabled {
 		have["runtime/cgo"] = true // ignore during walk
 	}
-	var pkgs []string
 
 	for _, src := range cfg.BuildContext.SrcDirs() {
 		if (pattern == "std" || pattern == "cmd") && src != cfg.GOROOTsrc {
@@ -123,11 +112,11 @@ func MatchPackages(pattern string) []string {
 				return nil
 			}
 
-			pkgs = append(pkgs, name)
+			m.Pkgs = append(m.Pkgs, name)
 			return nil
 		})
 	}
-	return pkgs
+	return m
 }
 
 var modRoot string
@@ -136,10 +125,16 @@ func SetModRoot(dir string) {
 	modRoot = dir
 }
 
-// MatchPackagesInFS returns a list of package paths matching pattern,
-// which must begin with ./ or ../
-// (see go help packages for pattern syntax).
-func MatchPackagesInFS(pattern string) []string {
+// MatchPackagesInFS is like allPackages but is passed a pattern
+// beginning ./ or ../, meaning it should scan the tree rooted
+// at the given directory. There are ... in the pattern too.
+// (See go help packages for pattern syntax.)
+func MatchPackagesInFS(pattern string) *Match {
+	m := &Match{
+		Pattern: pattern,
+		Literal: false,
+	}
+
 	// Find directory to begin the scan.
 	// Could be smarter but this one optimization
 	// is enough for now, since ... is usually at the
@@ -168,7 +163,6 @@ func MatchPackagesInFS(pattern string) []string {
 		}
 	}
 
-	var pkgs []string
 	filepath.Walk(dir, func(path string, fi os.FileInfo, err error) error {
 		if err != nil || !fi.IsDir() {
 			return nil
@@ -218,10 +212,10 @@ func MatchPackagesInFS(pattern string) []string {
 			}
 			return nil
 		}
-		pkgs = append(pkgs, name)
+		m.Pkgs = append(m.Pkgs, name)
 		return nil
 	})
-	return pkgs
+	return m
 }
 
 // TreeCanMatchPattern(pattern)(name) reports whether
@@ -308,36 +302,53 @@ func replaceVendor(x, repl string) string {
 	return strings.Join(elem, "/")
 }
 
-// ImportPaths returns the import paths to use for the given command line.
-func ImportPaths(args []string) []string {
-	args = CleanImportPaths(args)
-	var out []string
-	for _, a := range args {
+// WarnUnmatched warns about patterns that didn't match any packages.
+func WarnUnmatched(matches []*Match) {
+	for _, m := range matches {
+		if len(m.Pkgs) == 0 {
+			fmt.Fprintf(os.Stderr, "go: warning: %q matched no packages\n", m.Pattern)
+		}
+	}
+}
+
+// ImportPaths returns the matching paths to use for the given command line.
+// It calls ImportPathsQuiet and then WarnUnmatched.
+func ImportPaths(patterns []string) []*Match {
+	matches := ImportPathsQuiet(patterns)
+	WarnUnmatched(matches)
+	return matches
+}
+
+// ImportPathsQuiet is like ImportPaths but does not warn about patterns with no matches.
+func ImportPathsQuiet(patterns []string) []*Match {
+	var out []*Match
+	for _, a := range CleanPatterns(patterns) {
 		if IsMetaPackage(a) {
-			out = append(out, AllPackages(a)...)
+			out = append(out, MatchPackages(a))
 			continue
 		}
 		if strings.Contains(a, "...") {
 			if build.IsLocalImport(a) {
-				out = append(out, AllPackagesInFS(a)...)
+				out = append(out, MatchPackagesInFS(a))
 			} else {
-				out = append(out, AllPackages(a)...)
+				out = append(out, MatchPackages(a))
 			}
 			continue
 		}
-		out = append(out, a)
+		out = append(out, &Match{Pattern: a, Literal: true, Pkgs: []string{a}})
 	}
 	return out
 }
 
-// CleanImportPaths returns the import paths to use for the given
-// command line, but it does no wildcard expansion.
-func CleanImportPaths(args []string) []string {
-	if len(args) == 0 {
+// CleanPatterns returns the patterns to use for the given
+// command line. It canonicalizes the patterns but does not
+// evaluate any matches.
+func CleanPatterns(patterns []string) []string {
+	if len(patterns) == 0 {
 		return []string{"."}
 	}
 	var out []string
-	for _, a := range args {
+	for _, a := range patterns {
 		// Arguments are supposed to be import paths, but
 		// as a courtesy to Windows developers, rewrite \ to /
 		// in command-line arguments. Handles .\... and so on.
@@ -359,22 +370,6 @@ func CleanImportPaths(args []string) []string {
 	return out
 }
 
-// ImportPathsNoDotExpansion returns the import paths to use for the given
-// command line, but it does no ... expansion.
-// TODO(rsc): Delete once old go get is gone.
-func ImportPathsNoDotExpansion(args []string) []string {
-	args = CleanImportPaths(args)
-	var out []string
-	for _, a := range args {
-		if IsMetaPackage(a) {
-			out = append(out, AllPackages(a)...)
-			continue
-		}
-		out = append(out, a)
-	}
-	return out
-}
-
 // IsMetaPackage checks if name is a reserved package name that expands to multiple packages.
 func IsMetaPackage(name string) bool {
 	return name == "std" || name == "cmd" || name == "all"
diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 891f81e116..ed41ce5d07 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/src/cmd/go/internal/work/build.go
@@ -414,7 +414,7 @@ func libname(args []string, pkgs []*load.Package) (string, error) {
 
 func runInstall(cmd *base.Command, args []string) {
 	BuildInit()
-	InstallPackages(args)
+	InstallPackages(args, load.PackagesForBuild(args))
 }
 
 // omitTestOnly returns pkgs with test-only packages removed.
@@ -434,12 +434,12 @@ func omitTestOnly(pkgs []*load.Package) []*load.Package {
 	return list
 }
 
-func InstallPackages(args []string) {
+func InstallPackages(patterns []string, pkgs []*load.Package) {
 	if cfg.GOBIN != "" && !filepath.IsAbs(cfg.GOBIN) {
 		base.Fatalf("cannot install, GOBIN must be an absolute path")
 	}
 
-	pkgs := omitTestOnly(pkgsFilter(load.PackagesForBuild(args)))
+	pkgs = omitTestOnly(pkgsFilter(pkgs))
 	for _, p := range pkgs {
 		if p.Target == "" {
 			switch {
@@ -500,7 +500,7 @@ func InstallPackages(args []string) {
 		// tools above did not apply, and a is just a simple Action
 		// with a list of Deps, one per package named in pkgs,
 		// the same as in runBuild.
-		a = b.buildmodeShared(ModeInstall, ModeInstall, args, pkgs, a)
+		a = b.buildmodeShared(ModeInstall, ModeInstall, patterns, pkgs, a)
 	}
 
 	b.Do(a)
@@ -515,7 +515,7 @@ func InstallPackages(args []string) {
 	// One way to view this behavior is that it is as if 'go install' first
 	// runs 'go build' and the moves the generated file to the install dir.
 	// See issue 9645.
-	if len(args) == 0 && len(pkgs) == 1 && pkgs[0].Name == "main" {
+	if len(patterns) == 0 && len(pkgs) == 1 && pkgs[0].Name == "main" {
 		// Compute file 'go build' would have created.
 		// If it exists and is an executable file, remove it.
 		_, targ := filepath.Split(pkgs[0].ImportPath)
diff --git a/src/cmd/go/main.go b/src/cmd/go/main.go
index 59d367edaa..0639b4d2ca 100644
--- a/src/cmd/go/main.go
+++ b/src/cmd/go/main.go
@@ -64,6 +64,7 @@ func init() {
 		help.HelpCache,
 		help.HelpEnvironment,
 		help.HelpFileType,
+		modload.HelpGoMod,
 		help.HelpGopath,
 		get.HelpGopathGet,
 		modfetch.HelpGoproxy,
diff --git a/src/cmd/go/testdata/script/gcflags_patterns.txt b/src/cmd/go/testdata/script/gcflags_patterns.txt
new file mode 100644
index 0000000000..fe2cf6f0fb
--- /dev/null
+++ b/src/cmd/go/testdata/script/gcflags_patterns.txt
@@ -0,0 +1,71 @@
+[!gc] skip 'using -gcflags and -ldflags'
+
+# -gcflags=-e applies to named packages, not dependencies
+go build -n -v -gcflags=-e z1 z2
+stderr 'compile.* -e .*-p z1'
+stderr 'compile.* -e .*-p z2'
+stderr 'compile.* -p y'
+! stderr 'compile.* -e .*-p [^z]'
+
+# -gcflags can specify package=flags, and can be repeated; last match wins
+go build -n -v -gcflags=-e -gcflags=z1=-N z1 z2
+stderr 'compile.* -N .*-p z1'
+! stderr 'compile.* -e .*-p z1'
+! stderr 'compile.* -N .*-p z2'
+stderr 'compile.* -e .*-p z2'
+stderr 'compile.* -p y'
+! stderr 'compile.* -e .*-p [^z]'
+! stderr 'compile.* -N .*-p [^z]'
+
+# -gcflags can have arbitrary spaces around the flags
+go build -n -v -gcflags='  z1 =  	-e 	' z1
+stderr 'compile.* -e .*-p z1'
+
+# -ldflags for implicit test package applies to test binary
+go test -c -n -gcflags=-N -ldflags=-X=x.y=z z1
+stderr 'compile.* -N .*z_test.go'
+stderr 'link.* -X=x.y=z'
+
+# -ldflags for explicit test package applies to test binary
+go test -c -n -gcflags=z1=-N -ldflags=z1=-X=x.y=z z1
+stderr 'compile.* -N .*z_test.go'
+stderr 'link.* -X=x.y=z'
+
+# -ldflags applies to link of command
+go build -n -ldflags=-X=math.pi=3 my/cmd/prog
+stderr 'link.* -X=math.pi=3'
+
+# -ldflags applies to link of command even with strange directory name
+go build -n -ldflags=-X=math.pi=3 my/cmd/prog/
+stderr 'link.* -X=math.pi=3'
+
+# -ldflags applies to current directory
+cd my/cmd/prog
+go build -n -ldflags=-X=math.pi=3
+stderr 'link.* -X=math.pi=3'
+
+# -ldflags applies to current directory even if GOPATH is funny
+[windows] cd $WORK/GoPath/src/my/cmd/prog
+[darwin] cd $WORK/GoPath/src/my/cmd/prog
+go build -n -ldflags=-X=math.pi=3
+stderr 'link.* -X=math.pi=3'
+
+-- z1/z.go --
+package z1
+import _ "y"
+import _ "z2"
+
+-- z1/z_test.go --
+package z1_test
+import "testing"
+func Test(t *testing.T) {}
+
+-- z2/z.go --
+package z2
+
+-- y/y.go --
+package y
+
+-- my/cmd/prog/prog.go --
+package main
+func main() {}
diff --git a/src/cmd/go/testdata/script/mod_enabled.txt b/src/cmd/go/testdata/script/mod_enabled.txt
index 4901b9c5e6..8eef870b02 100644
--- a/src/cmd/go/testdata/script/mod_enabled.txt
+++ b/src/cmd/go/testdata/script/mod_enabled.txt
@@ -65,6 +65,15 @@ cd $GOPATH/foo/bar/baz
 go env GOMOD
 ! stdout .+
 
+# GO111MODULE=auto should ignore and warn about /tmp/go.mod
+env GO111MODULE=auto
+cp $GOPATH/src/x/y/z/go.mod $WORK/tmp/go.mod
+mkdir $WORK/tmp/mydir
+cd $WORK/tmp/mydir
+go env GOMOD
+! stdout .+
+stderr '^go: warning: ignoring go.mod in system temp root '
+
 -- $GOPATH/src/x/y/z/go.mod --
 module x/y/z
 -- $GOPATH/src/x/y/z/w/w.txt --
diff --git a/src/cmd/go/testdata/script/mod_fs_patterns.txt b/src/cmd/go/testdata/script/mod_fs_patterns.txt
index b5350c3eed..d7d3e0321b 100644
--- a/src/cmd/go/testdata/script/mod_fs_patterns.txt
+++ b/src/cmd/go/testdata/script/mod_fs_patterns.txt
@@ -28,6 +28,18 @@ stdout ^m/vendor$
 stdout ^m/y$
 ! stdout ^m/y/z
 
+# non-existent directory should not prompt lookups
+! go build -mod=readonly example.com/nonexist
+stderr 'import lookup disabled'
+
+! go build -mod=readonly ./nonexist
+! stderr 'import lookup disabled'
+stderr '^go: no such directory ./nonexist'
+
+! go build -mod=readonly ./go.mod
+! stderr 'import lookup disabled'
+stderr '^go: ./go.mod is not a directory'
+
 -- x/go.mod --
 module m
 
diff --git a/src/cmd/go/testdata/script/mod_get_commit.txt b/src/cmd/go/testdata/script/mod_get_commit.txt
index 2608397404..589a791fd4 100644
--- a/src/cmd/go/testdata/script/mod_get_commit.txt
+++ b/src/cmd/go/testdata/script/mod_get_commit.txt
@@ -45,8 +45,8 @@ grep 'rsc.io/quote v1.5.1' go.mod
 go mod edit -require rsc.io/quote@23179ee
 grep 'rsc.io/quote 23179ee' go.mod
 
-# but go mod fix fixes them
-go mod fix
+# but other commands fix them
+go mod graph
 grep 'rsc.io/quote v1.5.1' go.mod
 
 -- go.mod --
diff --git a/src/cmd/go/testdata/script/mod_list_dir.txt b/src/cmd/go/testdata/script/mod_list_dir.txt
index 29cde71fb8..800f277559 100644
--- a/src/cmd/go/testdata/script/mod_list_dir.txt
+++ b/src/cmd/go/testdata/script/mod_list_dir.txt
@@ -9,11 +9,14 @@ go list -f '{{.ImportPath}}' $GOROOT/src/math
 stdout ^math$
 go list -f '{{.ImportPath}}' .
 stdout ^x$
+! go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/quote@v1.5.2
+stderr '^go: no such directory.*quote@v1.5.2'
+go mod download rsc.io/quote@v1.5.2
 go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/quote@v1.5.2
 stdout '^rsc.io/quote$'
 go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/sampler@v1.3.0
 stdout '^rsc.io/sampler$'
-go get rsc.io/sampler@v1.3.1
+go get -d rsc.io/sampler@v1.3.1
 go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/sampler@v1.3.1
 stdout '^rsc.io/sampler$'
 ! go list -f '{{.ImportPath}}' $GOPATH/pkg/mod/rsc.io/sampler@v1.3.0
diff --git a/src/cmd/go/testdata/script/mod_patterns.txt b/src/cmd/go/testdata/script/mod_patterns.txt
index 36d738a867..4fa436ba2d 100644
--- a/src/cmd/go/testdata/script/mod_patterns.txt
+++ b/src/cmd/go/testdata/script/mod_patterns.txt
@@ -5,43 +5,34 @@ cd m
 # 'go list all' should list all of the packages used (directly or indirectly) by
 # the packages in the main module, but no other packages from the standard
 # library or active modules.
-go list all
-stdout example.com/m/useunicode
-stdout example.com/m/useunsafe
-[cgo] stdout example.com/m/useC
-[!cgo] ! stdout example.com/m/useC
-stdout '^unicode$'
-stdout '^unsafe$'
-! stdout index/suffixarray
-
+#
 # 'go list ...' should list packages in all active modules and the standard library.
 # But not cmd/* - see golang.org/issue/26924.
-go list ...
-stdout example.com/unused/useerrors
-stdout example.com/m/useunsafe
-[cgo] stdout example.com/m/useC
+#
+# 'go list example.com/m/...' should list packages in all modules that begin with 'example.com/m/'.
+#
+# 'go list ./...' should list only packages in the current module, not other active modules.
+#
+# Warnings about unmatched patterns should only be printed once.
+#
+# And the go command should be able to keep track of all this!
+go list -f '{{.ImportPath}}: {{.Match}}' all ... example.com/m/... ./... ./xyz...
+stdout 'example.com/m/useunicode: \[all \.\.\. example.com/m/... ./...\]'
+stdout 'example.com/m/useunsafe: \[all \.\.\. example.com/m/... ./...\]'
+[cgo] stdout 'example.com/m/useC: \[all \.\.\. example.com/m/... ./...\]'
 [!cgo] ! stdout example.com/m/useC
-stdout '^unicode$'
-stdout '^unsafe$'
-stdout index/suffixarray
-! stdout cmd/pprof
+stdout 'example.com/unused/useerrors: \[\.\.\.\]' # but not "all"
+stdout 'example.com/m/nested/useencoding: \[\.\.\. example.com/m/...\]' # but NOT "all" or "./..."
+stdout '^unicode: \[all \.\.\.\]'
+stdout '^unsafe: \[all \.\.\.\]'
+stdout 'index/suffixarray: \[\.\.\.\]'
+! stdout cmd/pprof # golang.org/issue/26924
 
-# 'go list example.com/m/...' should list packages in all modules that begin with
-# "example.com/m/".
-go list example.com/m/...
-stdout example.com/m/useunicode
-stdout example.com/m/useunsafe
-! stdout example.com/[^m]
-! stdout ^[^e]
-[cgo] stdout example.com/m/useC
-[!cgo] ! stdout example.com/m/useC
+stderr -count=1 '^go: warning: "./xyz..." matched no packages$'
 
-# 'go list ./...' should list only packages in the current module, not other active modules.
-go list ./...
-stdout example.com/m/useunicode
-stdout example.com/m/useunsafe
-[cgo] stdout example.com/m/useC
-[!cgo] ! stdout example.com/m/useC
+env CGO_ENABLED=0
+go list -f '{{.ImportPath}}: {{.Match}}' all ... example.com/m/... ./... ./xyz...
+! stdout example.com/m/useC
 
 -- m/go.mod --
 module example.com/m
diff --git a/src/cmd/go/testdata/script/mod_run_internal.txt b/src/cmd/go/testdata/script/mod_run_internal.txt
new file mode 100644
index 0000000000..653ad282be
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_run_internal.txt
@@ -0,0 +1,46 @@
+env GO111MODULE=on
+
+go list -e -f '{{.Incomplete}}' runbad1.go
+stdout true
+! go run runbad1.go
+stderr 'use of internal package m/x/internal not allowed'
+
+go list -e -f '{{.Incomplete}}' runbad2.go
+stdout true
+! go run runbad2.go
+stderr 'use of internal package m/x/internal/y not allowed'
+
+go list -e -f '{{.Incomplete}}' runok.go
+stdout false
+go run runok.go
+
+-- go.mod --
+module m
+
+-- x/internal/internal.go --
+package internal
+
+-- x/internal/y/y.go --
+package y
+
+-- internal/internal.go --
+package internal
+
+-- internal/z/z.go --
+package z
+
+-- runbad1.go --
+package main
+import _ "m/x/internal"
+func main() {}
+
+-- runbad2.go --
+package main
+import _ "m/x/internal/y"
+func main() {}
+
+-- runok.go --
+package main
+import _ "m/internal"
+import _ "m/internal/z"
+func main() {}
diff --git a/src/cmd/go/testdata/script/mod_run_path.txt b/src/cmd/go/testdata/script/mod_run_path.txt
new file mode 100644
index 0000000000..4369ee4131
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_run_path.txt
@@ -0,0 +1,15 @@
+# Test that go run does not get confused by conflict
+# between go.mod's module path and what you'd
+# expect from GOPATH. golang.org/issue/26046.
+
+env GO111MODULE=on
+
+cd $GOPATH/src/example.com/hello
+go run main.go
+
+-- $GOPATH/src/example.com/hello/go.mod --
+module example.com/hello/v2
+
+-- $GOPATH/src/example.com/hello/main.go --
+package main
+func main() {}
diff --git a/src/cmd/go/testdata/script/mod_tidy.txt b/src/cmd/go/testdata/script/mod_tidy.txt
index 86434af7f3..449aa073a7 100644
--- a/src/cmd/go/testdata/script/mod_tidy.txt
+++ b/src/cmd/go/testdata/script/mod_tidy.txt
@@ -10,6 +10,10 @@ go list -m all
 stdout '^w.1 v1.2.0'
 stdout '^z.1 v1.2.0'
 
+# empty tidy should not crash
+cd triv
+go mod tidy
+
 -- go.mod --
 module m
 
@@ -55,3 +59,6 @@ module z
 
 -- z/sub/sub.go --
 package sub
+
+-- triv/go.mod --
+module triv
diff --git a/src/cmd/go/testdata/script/mod_vcs_missing.txt b/src/cmd/go/testdata/script/mod_vcs_missing.txt
new file mode 100644
index 0000000000..fb146b4415
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_vcs_missing.txt
@@ -0,0 +1,11 @@
+[exec:bzr] skip 'tests NOT having bzr'
+[!net] skip
+
+env GO111MODULE=on
+env GOPROXY=
+
+! go list launchpad.net/gocheck
+stderr '"bzr": executable file not found'
+
+-- go.mod --
+module m
diff --git a/src/cmd/vet/print.go b/src/cmd/vet/print.go
index 90fd4ed379..a55da1d3c8 100644
--- a/src/cmd/vet/print.go
+++ b/src/cmd/vet/print.go
@@ -259,6 +259,20 @@ func checkPrintfFwd(pkg *Package, w *printfWrapper, call *ast.CallExpr, kind int
 	}
 
 	if !call.Ellipsis.IsValid() {
+		typ, ok := pkg.types[call.Fun].Type.(*types.Signature)
+		if !ok {
+			return
+		}
+		if len(call.Args) > typ.Params().Len() {
+			// If we're passing more arguments than what the
+			// print/printf function can take, adding an ellipsis
+			// would break the program. For example:
+			//
+			//   func foo(arg1 string, arg2 ...interface{} {
+			//       fmt.Printf("%s %v", arg1, arg2)
+			//   }
+			return
+		}
 		if !vcfg.VetxOnly {
 			desc := "printf"
 			if kind == kindPrint {
diff --git a/src/cmd/vet/testdata/print.go b/src/cmd/vet/testdata/print.go
index 7c0cbcf05a..ecafed5fa2 100644
--- a/src/cmd/vet/testdata/print.go
+++ b/src/cmd/vet/testdata/print.go
@@ -446,6 +446,10 @@ func (*ptrStringer) BadWrapf(x int, format string, args ...interface{}) string {
 	return fmt.Sprintf(format, args) // ERROR "missing ... in args forwarded to printf-like function"
 }
 
+func (*ptrStringer) WrapfFalsePositive(x int, arg1 string, arg2 ...interface{}) string {
+	return fmt.Sprintf("%s %v", arg1, arg2)
+}
+
 type embeddedStringer struct {
 	foo string
 	ptrStringer
diff --git a/src/go/doc/comment.go b/src/go/doc/comment.go
index 7c4490e7c3..d068d8960c 100644
--- a/src/go/doc/comment.go
+++ b/src/go/doc/comment.go
@@ -232,7 +232,7 @@ func heading(line string) string {
 	}
 
 	// exclude lines with illegal characters. we allow "(),"
-	if strings.ContainsAny(line, ".;:!?+*/=[]{}_^°&§~%#@<\">\\") {
+	if strings.ContainsAny(line, ";:!?+*/=[]{}_^°&§~%#@<\">\\") {
 		return ""
 	}
 
@@ -248,6 +248,18 @@ func heading(line string) string {
 		b = b[i+2:]
 	}
 
+	// allow "." when followed by non-space
+	for b := line;; {
+		i := strings.IndexRune(b, '.')
+		if i < 0 {
+			break
+		}
+		if i+1 >= len(b) || b[i+1] == ' ' {
+			return "" // not followed by non-space
+		}
+		b = b[i+1:]
+	}
+
 	return line
 }
 
diff --git a/src/go/printer/nodes.go b/src/go/printer/nodes.go
index 3723f30e56..1de7cd81b2 100644
--- a/src/go/printer/nodes.go
+++ b/src/go/printer/nodes.go
@@ -32,8 +32,10 @@ import (
 
 // Print as many newlines as necessary (but at least min newlines) to get to
 // the current line. ws is printed before the first line break. If newSection
-// is set, the first line break is printed as formfeed. Returns true if any
-// line break was printed; returns false otherwise.
+// is set, the first line break is printed as formfeed. Returns 0 if no line
+// breaks were printed, returns 1 if there was exactly one newline printed,
+// and returns a value > 1 if there was a formfeed or more than one newline
+// printed.
 //
 // TODO(gri): linebreak may add too many lines if the next statement at "line"
 //            is preceded by comments because the computation of n assumes
@@ -43,7 +45,7 @@ import (
 //            linebreaks. At the moment there is no easy way to know about
 //            future (not yet interspersed) comments in this function.
 //
-func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (printedBreak bool) {
+func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (nbreaks int) {
 	n := nlimit(line - p.pos.Line)
 	if n < min {
 		n = min
@@ -53,11 +55,12 @@ func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (prin
 		if newSection {
 			p.print(formfeed)
 			n--
+			nbreaks = 2
 		}
+		nbreaks += n
 		for ; n > 0; n-- {
 			p.print(newline)
 		}
-		printedBreak = true
 	}
 	return
 }
@@ -173,7 +176,7 @@ func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exp
 	// The first linebreak is always a formfeed since this section must not
 	// depend on any previous formatting.
 	prevBreak := -1 // index of last expression that was followed by a linebreak
-	if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) {
+	if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) > 0 {
 		ws = ignore
 		prevBreak = 0
 	}
@@ -221,36 +224,19 @@ func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exp
 		// If the previous line and the current line had single-
 		// line-expressions and the key sizes are small or the
 		// ratio between the current key and the geometric mean
-		// does not exceed a threshold, align columns and do not use
-		// formfeed.
-		// If the previous line was an empty line, break the alignment.
-		// (The text/tabwriter will break alignment after an empty line
-		// even if we don't do anything here, but we can't see that; yet
-		// we need to reset the variables used in the geomean
-		// computation after an alignment break. Do it explicitly
-		// instead so we're aware of the break. Was issue #26352.)
+		// if the previous key sizes does not exceed a threshold,
+		// align columns and do not use formfeed.
 		if prevSize > 0 && size > 0 {
 			const smallSize = 40
-			switch {
-			case prevLine+1 < line:
-				useFF = true
-			case count == 0, prevSize <= smallSize && size <= smallSize:
+			if count == 0 || prevSize <= smallSize && size <= smallSize {
 				useFF = false
-			default:
+			} else {
 				const r = 2.5                               // threshold
 				geomean := math.Exp(lnsum / float64(count)) // count > 0
 				ratio := float64(size) / geomean
 				useFF = r*ratio <= 1 || r <= ratio
 			}
 		}
-		if useFF {
-			lnsum = 0
-			count = 0
-		}
-		if size > 0 {
-			lnsum += math.Log(float64(size))
-			count++
-		}
 
 		needsLinebreak := 0 < prevLine && prevLine < line
 		if i > 0 {
@@ -266,11 +252,20 @@ func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exp
 				// Lines are broken using newlines so comments remain aligned
 				// unless useFF is set or there are multiple expressions on
 				// the same line in which case formfeed is used.
-				if p.linebreak(line, 0, ws, useFF || prevBreak+1 < i) {
+				nbreaks := p.linebreak(line, 0, ws, useFF || prevBreak+1 < i)
+				if nbreaks > 0 {
 					ws = ignore
 					prevBreak = i
 					needsBlank = false // we got a line break instead
 				}
+				// If there was a new section or more than one new line
+				// (which means that the tabwriter will implicitly break
+				// the section), reset the geomean variables since we are
+				// starting a new group of elements with the next element.
+				if nbreaks > 1 {
+					lnsum = 0
+					count = 0
+				}
 			}
 			if needsBlank {
 				p.print(blank)
@@ -290,6 +285,11 @@ func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exp
 			p.expr0(x, depth)
 		}
 
+		if size > 0 {
+			lnsum += math.Log(float64(size))
+			count++
+		}
+
 		prevLine = line
 	}
 
@@ -347,7 +347,7 @@ func (p *printer) parameters(fields *ast.FieldList) {
 				p.print(token.COMMA)
 			}
 			// separator if needed (linebreak or blank)
-			if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) {
+			if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) > 0 {
 				// break line if the opening "(" or previous parameter ended on a different line
 				ws = ignore
 			} else if i > 0 {
@@ -718,7 +718,7 @@ func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int) {
 	if xline != yline && xline > 0 && yline > 0 {
 		// at least one line break, but respect an extra empty line
 		// in the source
-		if p.linebreak(yline, 1, ws, true) {
+		if p.linebreak(yline, 1, ws, true) > 0 {
 			ws = ignore
 			printBlank = false // no blank after line break
 		}
diff --git a/src/go/printer/testdata/alignment.golden b/src/go/printer/testdata/alignment.golden
index 302b32e766..96086ed906 100644
--- a/src/go/printer/testdata/alignment.golden
+++ b/src/go/printer/testdata/alignment.golden
@@ -131,9 +131,42 @@ func main() {
 
 // ----------------------------------------------------------------------------
 // Examples from issue #26352.
+
 var _ = map[int]string{
 	1:	"",
 
 	12345678901234567890123456789:		"",
 	12345678901234567890123456789012345678:	"",
 }
+
+func f() {
+	_ = map[int]string{
+		1:	"",
+
+		12345678901234567:				"",
+		12345678901234567890123456789012345678901:	"",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #26930.
+
+var _ = S{
+	F1:	[]string{},
+	F2____:	[]string{},
+}
+
+var _ = S{
+	F1:	[]string{},
+	F2____:	[]string{},
+}
+
+var _ = S{
+	F1____:	[]string{},
+	F2:	[]string{},
+}
+
+var _ = S{
+	F1____:	[]string{},
+	F2:	[]string{},
+}
diff --git a/src/go/printer/testdata/alignment.input b/src/go/printer/testdata/alignment.input
index 83361cc7c1..323d2689e0 100644
--- a/src/go/printer/testdata/alignment.input
+++ b/src/go/printer/testdata/alignment.input
@@ -131,9 +131,49 @@ func main() {
 
 // ----------------------------------------------------------------------------
 // Examples from issue #26352.
+
 var _ = map[int]string{
 	1: "",
 
 	12345678901234567890123456789: "",
 	12345678901234567890123456789012345678: "",
 }
+
+func f() {
+	_ = map[int]string{
+		1: "",
+
+		12345678901234567: "",
+		12345678901234567890123456789012345678901: "",
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Examples from issue #26930.
+
+var _ = S{
+	F1: []string{
+	},
+	F2____: []string{},
+}
+
+var _ = S{
+	F1: []string{
+
+
+	},
+	F2____: []string{},
+}
+
+var _ = S{
+	F1____: []string{
+	},
+	F2: []string{},
+}
+
+var _ = S{
+	F1____: []string{
+
+	},
+	F2: []string{},
+}
diff --git a/src/os/file_plan9.go b/src/os/file_plan9.go
index 3a0b774aa2..2c74403434 100644
--- a/src/os/file_plan9.go
+++ b/src/os/file_plan9.go
@@ -478,7 +478,12 @@ func (f *File) Chown(uid, gid int) error {
 }
 
 func tempDir() string {
-	return "/tmp"
+	dir := Getenv("TMPDIR")
+	if dir == "" {
+		dir = "/tmp"
+	}
+	return dir
+
 }
 
 // Chdir changes the current working directory to the file,
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index a3193b63c5..ad47d1275e 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -842,11 +842,11 @@ var (
 	lfenceBeforeRdtsc    bool
 
 	// Set in runtime.cpuinit.
-	support_erms         bool
-	support_popcnt       bool
-	support_sse2         bool
-	support_sse41        bool
-	arm64_support_atomics      bool
+	support_erms          bool
+	support_popcnt        bool
+	support_sse2          bool
+	support_sse41         bool
+	arm64_support_atomics bool
 
 	goarm                uint8 // set by cmd/link on arm systems
 	framepointer_enabled bool  // set by cmd/link
diff --git a/src/runtime/sys_darwin_amd64.s b/src/runtime/sys_darwin_amd64.s
index 2a2e7379ca..db74352613 100644
--- a/src/runtime/sys_darwin_amd64.s
+++ b/src/runtime/sys_darwin_amd64.s
@@ -306,7 +306,7 @@ TEXT runtime·mmap_trampoline(SB),NOSPLIT,$0
 	CMPQ	AX, $-1
 	JNE	ok
 	CALL	libc_error(SB)
-	MOVQ	(AX), DX		// errno
+	MOVLQSX	(AX), DX		// errno
 	XORL	AX, AX
 ok:
 	MOVQ	AX, 32(BX)
@@ -371,7 +371,7 @@ TEXT runtime·kevent_trampoline(SB),NOSPLIT,$0
 	CMPQ	AX, $-1
 	JNE	ok
 	CALL	libc_error(SB)
-	MOVQ	(AX), AX		// errno
+	MOVLQSX	(AX), AX		// errno
 	NEGQ	AX			// caller wants it as a negative error code
 ok:
 	POPQ	BP
diff --git a/src/runtime/sys_darwin_arm64.s b/src/runtime/sys_darwin_arm64.s
index 4f9d0b8d58..d7ba116b84 100644
--- a/src/runtime/sys_darwin_arm64.s
+++ b/src/runtime/sys_darwin_arm64.s
@@ -70,7 +70,7 @@ TEXT runtime·mmap_trampoline(SB),NOSPLIT,$0
 	CMP	R0, R2
 	BNE	ok
 	BL libc_error(SB)
-	MOVD	(R0), R1
+	MOVW	(R0), R1
 	MOVD	$0, R0
 ok:
 	MOVD	R0, 32(R19) // ret 1 p
@@ -277,7 +277,7 @@ TEXT runtime·kevent_trampoline(SB),NOSPLIT,$0
 	CMP	R0, R2
 	BNE	ok
 	BL libc_error(SB)
-	MOVD	(R0), R0	// errno
+	MOVW	(R0), R0	// errno
 	NEG	R0, R0	// caller wants it as a negative error code
 ok:
 	RET
diff --git a/test/closure4.go b/test/closure4.go
new file mode 100644
index 0000000000..ec4e0a18eb
--- /dev/null
+++ b/test/closure4.go
@@ -0,0 +1,21 @@
+// run
+
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Check that calling a nil func causes a proper panic.
+
+package main
+
+func main() {
+	defer func() {
+		err := recover()
+		if err == nil {
+			panic("panic expected")
+		}
+	}()
+
+	var f func()
+	f()
+}