[dev.typeparams] all: merge master (37f9a8f) into dev.typeparams

Conflicts:

- src/go/types/check_test.go

  CL 330629 fixed a bug in package qualification logic

- src/internal/buildcfg/exp.go

  CL 329930 make parseExperiments get go arch string as input param

Merge List:

+ 2021-06-25 37f9a8f69d go/types: fix a bug in package qualification logic
+ 2021-06-24 c309c89db5 reflect: document that InterfaceData is a low-entropy RNG
+ 2021-06-24 cce621431a cmd/compile: fix wrong type in SSA generation for OSLICE2ARRPTR
+ 2021-06-24 600a2a4ffb cmd/go: don't try to add replaced versions that won't be selected
+ 2021-06-24 a9bb38222a net: remove hard-coded timeout in dialClosedPort test helper
+ 2021-06-24 86d72fa2cb time: handle invalid UTF-8 byte sequences in quote to prevent panic
+ 2021-06-24 44a12e5f33 cmd/go: search breadth-first instead of depth-first for test dependency cycles
+ 2021-06-24 73496e0df0 net: use absDomainName in the Windows lookupPTR test helper
+ 2021-06-24 222ed1b38a os: enable TestFifoEOF on openbsd
+ 2021-06-22 0ebd5a8de0 cmd/go: update ToolTags based on GOARCH value
+ 2021-06-22 5bd09e5efc spec: unsafe.Add/Slice are not permitted in statement context
+ 2021-06-22 666315b4d3 runtime/internal/atomic: remove incorrect pointer indirection in comment
+ 2021-06-22 63daa774b5 go/types: guard against checking instantiation when generics is disabled
+ 2021-06-22 197a5ee2ab cmd/gofmt: remove stale documentation for the -G flag
+ 2021-06-22 9afd158eb2 go/parser: parse an ast.IndexExpr for a[]
+ 2021-06-21 1bd5a20e3c cmd/go: add a -go flag to 'go mod graph'
+ 2021-06-21 761edf71f6 cmd/internal/moddeps: use a temporary directory for GOMODCACHE if needed
+ 2021-06-21 a0400420ad cmd/internal/moddeps: use -mod=readonly instead of -mod=mod
+ 2021-06-21 3f9ec83b10 cmd/go: document GOPPC64 environment variable
+ 2021-06-21 20bdfba325 go/scanner: fall back to next() when encountering 0 bytes in parseIdentifier
+ 2021-06-21 44f9a3566c database/sql: fix deadlock test in prepare statement

Change-Id: I16490e8ea70ee65081f467223857033842da513a

38 files changed, 505 insertions, 122 deletions

diff --git a/doc/go1.17.html b/doc/go1.17.html
index 02cd18d037..22896c8c27 100644
--- a/doc/go1.17.html
+++ b/doc/go1.17.html
@@ -187,6 +187,13 @@ Do not send CLs removing the interior tags from such phrases.
   features.
 </p>
 
+<p><!-- golang.org/issue/46366 -->
+  The <code>go</code> <code>mod</code> <code>graph</code> subcommand also
+  supports the <code>-go</code> flag, which causes it to report the graph as
+  seen by the indicated Go version, showing dependencies that may otherwise be
+  pruned out by lazy loading.
+</p>
+
 <h4 id="module-deprecation-comments">Module deprecation comments</h4>
 
 <p><!-- golang.org/issue/40357 -->
diff --git a/doc/go_spec.html b/doc/go_spec.html
index 561d44271a..b59b37fd55 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification",
-	"Subtitle": "Version of Jun 2, 2021",
+	"Subtitle": "Version of Jun 22, 2021",
 	"Path": "/ref/spec"
 }-->
 
@@ -4670,7 +4670,7 @@ The following built-in functions are not permitted in statement context:
 
 <pre>
 append cap complex imag len make new real
-unsafe.Alignof unsafe.Offsetof unsafe.Sizeof
+unsafe.Add unsafe.Alignof unsafe.Offsetof unsafe.Sizeof unsafe.Slice
 </pre>
 
 <pre>
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 9212c5776e..2bf34b0a84 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -3106,7 +3106,7 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 		arrlen := s.constInt(types.Types[types.TINT], n.Type().Elem().NumElem())
 		cap := s.newValue1(ssa.OpSliceLen, types.Types[types.TINT], v)
 		s.boundsCheck(arrlen, cap, ssa.BoundsConvert, false)
-		return s.newValue1(ssa.OpSlicePtrUnchecked, types.Types[types.TINT], v)
+		return s.newValue1(ssa.OpSlicePtrUnchecked, n.Type(), v)
 
 	case ir.OCALLFUNC:
 		n := n.(*ir.CallExpr)
diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index 3febe880cd..fd95da23eb 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -1186,13 +1186,17 @@
 //
 // Usage:
 //
-// 	go mod graph
+// 	go mod graph [-go=version]
 //
 // Graph prints the module requirement graph (with replacements applied)
 // in text form. Each line in the output has two space-separated fields: a module
 // and one of its requirements. Each module is identified as a string of the form
 // path@version, except for the main module, which has no @version suffix.
 //
+// The -go flag causes graph to report the module graph as loaded by by the
+// given Go version, instead of the version indicated by the 'go' directive
+// in the go.mod file.
+//
 // See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
 //
 //
@@ -1887,6 +1891,9 @@
 // 	GOMIPS64
 // 		For GOARCH=mips64{,le}, whether to use floating point instructions.
 // 		Valid values are hardfloat (default), softfloat.
+// 	GOPPC64
+// 		For GOARCH=ppc64{,le}, the target ISA (Instruction Set Architecture).
+// 		Valid values are power8 (default), power9.
 // 	GOWASM
 // 		For GOARCH=wasm, comma-separated list of experimental WebAssembly features to use.
 // 		Valid values are satconv, signext.
diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index b47eb812b5..fc6989097e 100644
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -77,6 +77,14 @@ func defaultContext() build.Context {
 	ctxt.GOOS = envOr("GOOS", ctxt.GOOS)
 	ctxt.GOARCH = envOr("GOARCH", ctxt.GOARCH)
 
+	// The experiments flags are based on GOARCH, so they may
+	// need to change.  TODO: This should be cleaned up.
+	buildcfg.UpdateExperiments(ctxt.GOARCH)
+	ctxt.ToolTags = nil
+	for _, exp := range buildcfg.EnabledExperiments() {
+		ctxt.ToolTags = append(ctxt.ToolTags, "goexperiment."+exp)
+	}
+
 	// The go/build rule for whether cgo is enabled is:
 	//	1. If $CGO_ENABLED is set, respect it.
 	//	2. Otherwise, if this is a cross-compile, disable cgo.
diff --git a/src/cmd/go/internal/help/helpdoc.go b/src/cmd/go/internal/help/helpdoc.go
index 9ec6501892..b552777e3e 100644
--- a/src/cmd/go/internal/help/helpdoc.go
+++ b/src/cmd/go/internal/help/helpdoc.go
@@ -598,6 +598,9 @@ Architecture-specific environment variables:
 	GOMIPS64
 		For GOARCH=mips64{,le}, whether to use floating point instructions.
 		Valid values are hardfloat (default), softfloat.
+	GOPPC64
+		For GOARCH=ppc64{,le}, the target ISA (Instruction Set Architecture).
+		Valid values are power8 (default), power9.
 	GOWASM
 		For GOARCH=wasm, comma-separated list of experimental WebAssembly features to use.
 		Valid values are satconv, signext.
diff --git a/src/cmd/go/internal/load/test.go b/src/cmd/go/internal/load/test.go
index 6baa1db14f..c828296566 100644
--- a/src/cmd/go/internal/load/test.go
+++ b/src/cmd/go/internal/load/test.go
@@ -116,7 +116,7 @@ func TestPackagesAndErrors(ctx context.Context, opts PackageOpts, p *Package, co
 			// Can't change that code, because that code is only for loading the
 			// non-test copy of a package.
 			ptestErr = &PackageError{
-				ImportStack:   testImportStack(stk[0], p1, p.ImportPath),
+				ImportStack:   importCycleStack(p1, p.ImportPath),
 				Err:           errors.New("import cycle not allowed in test"),
 				IsImportCycle: true,
 			}
@@ -375,22 +375,44 @@ func TestPackagesAndErrors(ctx context.Context, opts PackageOpts, p *Package, co
 	return pmain, ptest, pxtest
 }
 
-func testImportStack(top string, p *Package, target string) []string {
-	stk := []string{top, p.ImportPath}
-Search:
-	for p.ImportPath != target {
-		for _, p1 := range p.Internal.Imports {
-			if p1.ImportPath == target || str.Contains(p1.Deps, target) {
-				stk = append(stk, p1.ImportPath)
-				p = p1
-				continue Search
+// importCycleStack returns an import stack from p to the package whose import
+// path is target.
+func importCycleStack(p *Package, target string) []string {
+	// importerOf maps each import path to its importer nearest to p.
+	importerOf := map[string]string{p.ImportPath: ""}
+
+	// q is a breadth-first queue of packages to search for target.
+	// Every package added to q has a corresponding entry in pathTo.
+	//
+	// We search breadth-first for two reasons:
+	//
+	// 	1. We want to report the shortest cycle.
+	//
+	// 	2. If p contains multiple cycles, the first cycle we encounter might not
+	// 	   contain target. To ensure termination, we have to break all cycles
+	// 	   other than the first.
+	q := []*Package{p}
+
+	for len(q) > 0 {
+		p := q[0]
+		q = q[1:]
+		if path := p.ImportPath; path == target {
+			var stk []string
+			for path != "" {
+				stk = append(stk, path)
+				path = importerOf[path]
+			}
+			return stk
+		}
+		for _, dep := range p.Internal.Imports {
+			if _, ok := importerOf[dep.ImportPath]; !ok {
+				importerOf[dep.ImportPath] = p.ImportPath
+				q = append(q, dep)
 			}
 		}
-		// Can't happen, but in case it does...
-		stk = append(stk, "<lost path to cycle>")
-		break
 	}
-	return stk
+
+	panic("lost path to cycle")
 }
 
 // recompileForTest copies and replaces certain packages in pmain's dependency
diff --git a/src/cmd/go/internal/modcmd/graph.go b/src/cmd/go/internal/modcmd/graph.go
index 77853304e9..903bd9970f 100644
--- a/src/cmd/go/internal/modcmd/graph.go
+++ b/src/cmd/go/internal/modcmd/graph.go
@@ -18,7 +18,7 @@ import (
 )
 
 var cmdGraph = &base.Command{
-	UsageLine: "go mod graph",
+	UsageLine: "go mod graph [-go=version]",
 	Short:     "print module requirement graph",
 	Long: `
 Graph prints the module requirement graph (with replacements applied)
@@ -26,12 +26,21 @@ in text form. Each line in the output has two space-separated fields: a module
 and one of its requirements. Each module is identified as a string of the form
 path@version, except for the main module, which has no @version suffix.
 
+The -go flag causes graph to report the module graph as loaded by by the
+given Go version, instead of the version indicated by the 'go' directive
+in the go.mod file.
+
 See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
 	`,
 	Run: runGraph,
 }
 
+var (
+	graphGo goVersionFlag
+)
+
 func init() {
+	cmdGraph.Flag.Var(&graphGo, "go", "")
 	base.AddModCommonFlags(&cmdGraph.Flag)
 }
 
@@ -41,7 +50,7 @@ func runGraph(ctx context.Context, cmd *base.Command, args []string) {
 	}
 	modload.ForceUseModules = true
 	modload.RootMode = modload.NeedRoot
-	mg := modload.LoadModGraph(ctx)
+	mg := modload.LoadModGraph(ctx, graphGo.String())
 
 	w := bufio.NewWriter(os.Stdout)
 	defer w.Flush()
diff --git a/src/cmd/go/internal/modcmd/verify.go b/src/cmd/go/internal/modcmd/verify.go
index 5c321c783a..5a6eca32cf 100644
--- a/src/cmd/go/internal/modcmd/verify.go
+++ b/src/cmd/go/internal/modcmd/verify.go
@@ -54,7 +54,8 @@ func runVerify(ctx context.Context, cmd *base.Command, args []string) {
 	sem := make(chan token, runtime.GOMAXPROCS(0))
 
 	// Use a slice of result channels, so that the output is deterministic.
-	mods := modload.LoadModGraph(ctx).BuildList()[1:]
+	const defaultGoVersion = ""
+	mods := modload.LoadModGraph(ctx, defaultGoVersion).BuildList()[1:]
 	errsChans := make([]<-chan []error, len(mods))
 
 	for i, mod := range mods {
diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index ea5c4e229a..9672e5598e 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -506,7 +506,8 @@ type versionReason struct {
 func newResolver(ctx context.Context, queries []*query) *resolver {
 	// LoadModGraph also sets modload.Target, which is needed by various resolver
 	// methods.
-	mg := modload.LoadModGraph(ctx)
+	const defaultGoVersion = ""
+	mg := modload.LoadModGraph(ctx, defaultGoVersion)
 
 	buildList := mg.BuildList()
 	initialVersion := make(map[string]string, len(buildList))
@@ -1803,7 +1804,8 @@ func (r *resolver) updateBuildList(ctx context.Context, additions []module.Versi
 		return false
 	}
 
-	r.buildList = modload.LoadModGraph(ctx).BuildList()
+	const defaultGoVersion = ""
+	r.buildList = modload.LoadModGraph(ctx, defaultGoVersion).BuildList()
 	r.buildListVersion = make(map[string]string, len(r.buildList))
 	for _, m := range r.buildList {
 		r.buildListVersion[m.Path] = m.Version
diff --git a/src/cmd/go/internal/modload/buildlist.go b/src/cmd/go/internal/modload/buildlist.go
index 64eaa16e8b..604a57b437 100644
--- a/src/cmd/go/internal/modload/buildlist.go
+++ b/src/cmd/go/internal/modload/buildlist.go
@@ -403,11 +403,33 @@ func (mg *ModuleGraph) allRootsSelected() bool {
 // LoadModGraph loads and returns the graph of module dependencies of the main module,
 // without loading any packages.
 //
+// If the goVersion string is non-empty, the returned graph is the graph
+// as interpreted by the given Go version (instead of the version indicated
+// in the go.mod file).
+//
 // Modules are loaded automatically (and lazily) in LoadPackages:
 // LoadModGraph need only be called if LoadPackages is not,
 // typically in commands that care about modules but no particular package.
-func LoadModGraph(ctx context.Context) *ModuleGraph {
-	rs, mg, err := expandGraph(ctx, LoadModFile(ctx))
+func LoadModGraph(ctx context.Context, goVersion string) *ModuleGraph {
+	rs := LoadModFile(ctx)
+
+	if goVersion != "" {
+		depth := modDepthFromGoVersion(goVersion)
+		if depth == eager && rs.depth != eager {
+			// Use newRequirements instead of convertDepth because convertDepth
+			// also updates roots; here, we want to report the unmodified roots
+			// even though they may seem inconsistent.
+			rs = newRequirements(eager, rs.rootModules, rs.direct)
+		}
+
+		mg, err := rs.Graph(ctx)
+		if err != nil {
+			base.Fatalf("go: %v", err)
+		}
+		return mg
+	}
+
+	rs, mg, err := expandGraph(ctx, rs)
 	if err != nil {
 		base.Fatalf("go: %v", err)
 	}
diff --git a/src/cmd/go/internal/modload/import.go b/src/cmd/go/internal/modload/import.go
index 60bd26fb22..d2bbe5cbe0 100644
--- a/src/cmd/go/internal/modload/import.go
+++ b/src/cmd/go/internal/modload/import.go
@@ -428,6 +428,15 @@ func queryImport(ctx context.Context, path string, rs *Requirements) (module.Ver
 					mv = module.ZeroPseudoVersion("v0")
 				}
 			}
+			mg, err := rs.Graph(ctx)
+			if err != nil {
+				return module.Version{}, err
+			}
+			if cmpVersion(mg.Selected(mp), mv) >= 0 {
+				// We can't resolve the import by adding mp@mv to the module graph,
+				// because the selected version of mp is already at least mv.
+				continue
+			}
 			mods = append(mods, module.Version{Path: mp, Version: mv})
 		}
 
diff --git a/src/cmd/go/testdata/script/env_cross_build.txt b/src/cmd/go/testdata/script/env_cross_build.txt
new file mode 100644
index 0000000000..3feeba6b14
--- /dev/null
+++ b/src/cmd/go/testdata/script/env_cross_build.txt
@@ -0,0 +1,29 @@
+# Test that the corect default GOEXPERIMENT is used when cross
+# building with GOENV (#46815).
+
+# Unset variables set by the TestScript harness. Users typically won't
+# explicitly configure these, and #46815 doesn't repro if they are.
+env GOOS=
+env GOARCH=
+env GOEXPERIMENT=
+
+env GOENV=windows-amd64
+go build internal/abi
+
+env GOENV=ios-arm64
+go build internal/abi
+
+env GOENV=linux-mips
+go build internal/abi
+
+-- windows-amd64 --
+GOOS=windows
+GOARCH=amd64
+
+-- ios-arm64 --
+GOOS=ios
+GOARCH=arm64
+
+-- linux-mips --
+GOOS=linux
+GOARCH=mips
diff --git a/src/cmd/go/testdata/script/mod_graph_version.txt b/src/cmd/go/testdata/script/mod_graph_version.txt
new file mode 100644
index 0000000000..f9a73f4617
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_graph_version.txt
@@ -0,0 +1,101 @@
+# For this module, Go 1.17 prunes out a (transitive and otherwise-irrelevant)
+# requirement on a retracted higher version of a dependency.
+# However, when Go 1.16 reads the same requirements from the go.mod file,
+# it does not prune out that requirement, and selects the retracted version.
+#
+# The Go 1.16 module graph looks like:
+#
+# m ---- lazy v0.1.0 ---- requireincompatible v0.1.0 ---- incompatible v2.0.0+incompatible
+# |        |
+# + -------+------------- incompatible v1.0.0
+#
+# The Go 1.17 module graph is the same except that the dependencies of
+# requireincompatible are pruned out (because the module that requires
+# it — lazy v0.1.0 — specifies 'go 1.17', and it is not otherwise relevant to
+# the main module).
+
+cp go.mod go.mod.orig
+
+go mod graph
+cp stdout graph-1.17.txt
+stdout '^example\.com/m example\.com/retract/incompatible@v1\.0\.0$'
+stdout '^example\.net/lazy@v0\.1\.0 example\.com/retract/incompatible@v1\.0\.0$'
+! stdout 'example\.com/retract/incompatible@v2\.0\.0\+incompatible'
+
+go mod graph -go=1.17
+cmp stdout graph-1.17.txt
+
+cmp go.mod go.mod.orig
+
+
+# Setting -go=1.16 should report the graph as viewed by Go 1.16,
+# but should not edit the go.mod file.
+
+go mod graph -go=1.16
+cp stdout graph-1.16.txt
+stdout '^example\.com/m example\.com/retract/incompatible@v1\.0\.0$'
+stdout '^example\.net/lazy@v0\.1\.0 example.com/retract/incompatible@v1\.0\.0$'
+stdout '^example.net/requireincompatible@v0.1.0 example.com/retract/incompatible@v2\.0\.0\+incompatible$'
+
+cmp go.mod go.mod.orig
+
+
+# If we actually update the go.mod file to the requested go version,
+# we should get the same selected versions, but the roots of the graph
+# may be updated.
+#
+# TODO(#45551): The roots should not be updated.
+
+go mod edit -go=1.16
+go mod graph
+! stdout '^example\.com/m example\.com/retract/incompatible@v1\.0\.0$'
+stdout '^example\.net/lazy@v0.1.0 example.com/retract/incompatible@v1\.0\.0$'
+stdout '^example.net/requireincompatible@v0.1.0 example.com/retract/incompatible@v2\.0\.0\+incompatible$'
+	# TODO(#45551): cmp stdout graph-1.16.txt
+
+
+# Unsupported go versions should be rejected, since we don't know
+# what versions they would report.
+! go mod graph -go=1.99999999999
+stderr '^invalid value "1\.99999999999" for flag -go: maximum supported Go version is '$goversion'\nusage: go mod graph \[-go=version\]\nRun ''go help mod graph'' for details.$'
+
+
+-- go.mod --
+// Module m indirectly imports a package from
+// example.com/retract/incompatible. Its selected version of
+// that module is lower under Go 1.17 semantics than under Go 1.16.
+module example.com/m
+
+go 1.17
+
+replace (
+	example.net/lazy v0.1.0 => ./lazy
+	example.net/requireincompatible v0.1.0 => ./requireincompatible
+)
+
+require (
+	example.com/retract/incompatible v1.0.0 // indirect
+	example.net/lazy v0.1.0
+)
+-- lazy/go.mod --
+// Module lazy requires example.com/retract/incompatible v1.0.0.
+//
+// When viewed from the outside it also has a transitive dependency
+// on v2.0.0+incompatible, but in lazy mode that transitive dependency
+// is pruned out.
+module example.net/lazy
+
+go 1.17
+
+exclude example.com/retract/incompatible v2.0.0+incompatible
+
+require (
+	example.com/retract/incompatible v1.0.0
+	example.net/requireincompatible v0.1.0
+)
+-- requireincompatible/go.mod --
+module example.net/requireincompatible
+
+go 1.15
+
+require example.com/retract/incompatible v2.0.0+incompatible
diff --git a/src/cmd/go/testdata/script/mod_list_test_cycle.txt b/src/cmd/go/testdata/script/mod_list_test_cycle.txt
new file mode 100644
index 0000000000..755e50b076
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_list_test_cycle.txt
@@ -0,0 +1,23 @@
+# https://golang.org/issue/45863: a typo in a test package leading to an
+# import cycle should be diagnosed, instead of causing an infinite loop.
+# The failure mode of this test prior to the fix was a timeout or OOM crash.
+
+go list -e -test -deps ./datastore/sql
+
+-- go.mod --
+module golang.org/issue45863
+
+go 1.17
+-- datastore/datastore_health.go --
+package datastore
+
+import (
+	"golang.org/issue45863/datastore"
+	"golang.org/issue45863/datastore/sql"
+)
+-- datastore/sql/sql.go --
+package sql
+-- datastore/sql/sql_test.go --
+package sql
+
+import _ "golang.org/issue45863/datastore"
diff --git a/src/cmd/go/testdata/script/mod_tidy_replace_old.txt b/src/cmd/go/testdata/script/mod_tidy_replace_old.txt
new file mode 100644
index 0000000000..cfd3792600
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_tidy_replace_old.txt
@@ -0,0 +1,34 @@
+# Regression test for https://golang.org/issue/46659.
+#
+# If a 'replace' directive specifies an older-than-selected version of a module,
+# 'go mod tidy' shouldn't try to add that version to the build list to resolve a
+# missing package: it won't be selected, and would cause the module loader to
+# loop indefinitely trying to resolve the package.
+
+cp go.mod go.mod.orig
+
+! go mod tidy
+! stderr panic
+stderr '^golang\.org/issue46659 imports\n\texample\.com/missingpkg/deprecated: package example\.com/missingpkg/deprecated provided by example\.com/missingpkg at latest version v1\.0\.0 but not at required version v1\.0\.1-beta$'
+
+go mod tidy -e
+
+cmp go.mod go.mod.orig
+
+-- go.mod --
+module golang.org/issue46659
+
+go 1.17
+
+replace example.com/missingpkg v1.0.1-alpha => example.com/missingpkg v1.0.0
+
+require example.com/usemissingpre v1.0.0
+
+require example.com/missingpkg v1.0.1-beta // indirect
+-- m.go --
+package m
+
+import (
+	_ "example.com/missingpkg/deprecated"
+	_ "example.com/usemissingpre"
+)
diff --git a/src/cmd/internal/moddeps/moddeps_test.go b/src/cmd/internal/moddeps/moddeps_test.go
index 7723250468..56c3b2585c 100644
--- a/src/cmd/internal/moddeps/moddeps_test.go
+++ b/src/cmd/internal/moddeps/moddeps_test.go
@@ -5,6 +5,7 @@
 package moddeps_test
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"internal/testenv"
@@ -68,7 +69,7 @@ func TestAllDependencies(t *testing.T) {
 
 			// There is no vendor directory, so the module must have no dependencies.
 			// Check that the list of active modules contains only the main module.
-			cmd := exec.Command(goBin, "list", "-mod=mod", "-m", "all")
+			cmd := exec.Command(goBin, "list", "-mod=readonly", "-m", "all")
 			cmd.Env = append(os.Environ(), "GO111MODULE=on")
 			cmd.Dir = m.Dir
 			cmd.Stderr = new(strings.Builder)
@@ -123,10 +124,38 @@ func TestAllDependencies(t *testing.T) {
 		t.Skip("skipping because a diff command with support for --recursive and --unified flags is unavailable")
 	}
 
+	// We're going to check the standard modules for tidiness, so we need a usable
+	// GOMODCACHE. If the default directory doesn't exist, use a temporary
+	// directory instead. (That can occur, for example, when running under
+	// run.bash with GO_TEST_SHORT=0: run.bash sets GOPATH=/nonexist-gopath, and
+	// GO_TEST_SHORT=0 causes it to run this portion of the test.)
+	var modcacheEnv []string
+	{
+		out, err := exec.Command(goBin, "env", "GOMODCACHE").Output()
+		if err != nil {
+			t.Fatalf("%s env GOMODCACHE: %v", goBin, err)
+		}
+		modcacheOk := false
+		if gomodcache := string(bytes.TrimSpace(out)); gomodcache != "" {
+			if _, err := os.Stat(gomodcache); err == nil {
+				modcacheOk = true
+			}
+		}
+		if !modcacheOk {
+			modcacheEnv = []string{
+				"GOMODCACHE=" + t.TempDir(),
+				"GOFLAGS=" + os.Getenv("GOFLAGS") + " -modcacherw", // Allow t.TempDir() to clean up subdirectories.
+			}
+		}
+	}
+
 	// Build the bundle binary at the golang.org/x/tools
 	// module version specified in GOROOT/src/cmd/go.mod.
 	bundleDir := t.TempDir()
-	r := runner{Dir: filepath.Join(runtime.GOROOT(), "src/cmd")}
+	r := runner{
+		Dir: filepath.Join(runtime.GOROOT(), "src/cmd"),
+		Env: append(os.Environ(), modcacheEnv...),
+	}
 	r.run(t, goBin, "build", "-mod=readonly", "-o", bundleDir, "golang.org/x/tools/cmd/bundle")
 
 	var gorootCopyDir string
@@ -160,7 +189,7 @@ func TestAllDependencies(t *testing.T) {
 			}
 			r := runner{
 				Dir: filepath.Join(gorootCopyDir, rel),
-				Env: append(os.Environ(),
+				Env: append(append(os.Environ(), modcacheEnv...),
 					// Set GOROOT.
 					"GOROOT="+gorootCopyDir,
 					// Explicitly override PWD and clear GOROOT_FINAL so that GOROOT=gorootCopyDir is definitely used.
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 7d1cb9b85a..f771dee4a9 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -2841,7 +2841,6 @@ func TestTxStmtDeadlock(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	tx, err := db.BeginTx(ctx, nil)
-	cancel()
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -2850,6 +2849,7 @@ func TestTxStmtDeadlock(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	cancel()
 	// Run number of stmt queries to reproduce deadlock from context cancel
 	for i := 0; i < 1e3; i++ {
 		// Encounter any close related errors (e.g. ErrTxDone, stmt is closed)
diff --git a/src/go/parser/parser.go b/src/go/parser/parser.go
index 869d14c2c1..c0a3cc66fe 100644
--- a/src/go/parser/parser.go
+++ b/src/go/parser/parser.go
@@ -1379,7 +1379,12 @@ func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
 		p.errorExpected(p.pos, "operand")
 		rbrack := p.pos
 		p.next()
-		return &ast.BadExpr{From: x.Pos(), To: rbrack}
+		return &ast.IndexExpr{
+			X:      x,
+			Lbrack: lbrack,
+			Index:  &ast.BadExpr{From: rbrack, To: rbrack},
+			Rbrack: rbrack,
+		}
 	}
 	p.exprLev++
 
diff --git a/src/go/scanner/scanner.go b/src/go/scanner/scanner.go
index f8bcf4d864..ca4b5264cf 100644
--- a/src/go/scanner/scanner.go
+++ b/src/go/scanner/scanner.go
@@ -373,7 +373,7 @@ func (s *Scanner) scanIdentifier() string {
 			continue
 		}
 		s.rdOffset += rdOffset
-		if b < utf8.RuneSelf {
+		if 0 < b && b < utf8.RuneSelf {
 			// Optimization: we've encountered an ASCII character that's not a letter
 			// or number. Avoid the call into s.next() and corresponding set up.
 			//
diff --git a/src/go/scanner/scanner_test.go b/src/go/scanner/scanner_test.go
index dd3c7cf838..de45e16606 100644
--- a/src/go/scanner/scanner_test.go
+++ b/src/go/scanner/scanner_test.go
@@ -813,6 +813,8 @@ var errors = []struct {
 	{"//\ufeff", token.COMMENT, 2, "//\ufeff", "illegal byte order mark"},                                // only first BOM is ignored
 	{"'\ufeff" + `'`, token.CHAR, 1, "'\ufeff" + `'`, "illegal byte order mark"},                         // only first BOM is ignored
 	{`"` + "abc\ufeffdef" + `"`, token.STRING, 4, `"` + "abc\ufeffdef" + `"`, "illegal byte order mark"}, // only first BOM is ignored
+	{"abc\x00def", token.IDENT, 3, "abc", "illegal character NUL"},
+	{"abc\x00", token.IDENT, 3, "abc", "illegal character NUL"},
 }
 
 func TestScanErrors(t *testing.T) {
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 0926ac7431..a5720f992e 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -202,17 +202,20 @@ func asGoVersion(s string) string {
 	return ""
 }
 
-func testFiles(t *testing.T, sizes Sizes, filenames []string, srcs [][]byte, manual bool) {
+func testFiles(t *testing.T, sizes Sizes, filenames []string, srcs [][]byte, manual bool, imp Importer) {
 	if len(filenames) == 0 {
 		t.Fatal("no source files")
 	}
 
+	if strings.HasSuffix(filenames[0], ".go2") && !typeparams.Enabled {
+		t.Skip("type params are not enabled")
+	}
+	if strings.HasSuffix(filenames[0], ".go1") && typeparams.Enabled {
+		t.Skip("type params are enabled")
+	}
+
 	mode := parser.AllErrors
-	if strings.HasSuffix(filenames[0], ".go2") {
-		if !typeparams.Enabled {
-			t.Skip("type params are not enabled")
-		}
-	} else {
+	if !strings.HasSuffix(filenames[0], ".go2") {
 		mode |= typeparams.DisallowParsing
 	}
 
@@ -250,7 +253,10 @@ func testFiles(t *testing.T, sizes Sizes, filenames []string, srcs [][]byte, man
 		}
 	}
 
-	conf.Importer = importer.Default()
+	conf.Importer = imp
+	if imp == nil {
+		conf.Importer = importer.Default()
+	}
 	conf.Error = func(err error) {
 		if *haltOnError {
 			defer panic(err)
@@ -339,7 +345,7 @@ func TestManual(t *testing.T) {
 func TestLongConstants(t *testing.T) {
 	format := "package longconst\n\nconst _ = %s\nconst _ = %s // ERROR excessively long constant"
 	src := fmt.Sprintf(format, strings.Repeat("1", 9999), strings.Repeat("1", 10001))
-	testFiles(t, nil, []string{"longconst.go"}, [][]byte{[]byte(src)}, false)
+	testFiles(t, nil, []string{"longconst.go"}, [][]byte{[]byte(src)}, false, nil)
 }
 
 // TestIndexRepresentability tests that constant index operands must
@@ -347,7 +353,7 @@ func TestLongConstants(t *testing.T) {
 // represent larger values.
 func TestIndexRepresentability(t *testing.T) {
 	const src = "package index\n\nvar s []byte\nvar _ = s[int64 /* ERROR \"int64\\(1\\) << 40 \\(.*\\) overflows int\" */ (1) << 40]"
-	testFiles(t, &StdSizes{4, 4}, []string{"index.go"}, [][]byte{[]byte(src)}, false)
+	testFiles(t, &StdSizes{4, 4}, []string{"index.go"}, [][]byte{[]byte(src)}, false, nil)
 }
 
 func TestIssue46453(t *testing.T) {
@@ -355,7 +361,7 @@ func TestIssue46453(t *testing.T) {
 		t.Skip("type params are enabled")
 	}
 	const src = "package p\ntype _ comparable // ERROR \"undeclared name: comparable\""
-	testFiles(t, nil, []string{"issue46453.go"}, [][]byte{[]byte(src)}, false)
+	testFiles(t, nil, []string{"issue46453.go"}, [][]byte{[]byte(src)}, false, nil)
 }
 
 func TestCheck(t *testing.T)     { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/check", false) }
@@ -415,5 +421,5 @@ func testPkg(t *testing.T, filenames []string, manual bool) {
 		}
 		srcs[i] = src
 	}
-	testFiles(t, nil, filenames, srcs, manual)
+	testFiles(t, nil, filenames, srcs, manual, nil)
 }
diff --git a/src/go/types/errors.go b/src/go/types/errors.go
index 19e9ae8d44..2263106417 100644
--- a/src/go/types/errors.go
+++ b/src/go/types/errors.go
@@ -31,7 +31,7 @@ func (check *Checker) qualifier(pkg *Package) string {
 		if check.pkgPathMap == nil {
 			check.pkgPathMap = make(map[string]map[string]bool)
 			check.seenPkgMap = make(map[*Package]bool)
-			check.markImports(pkg)
+			check.markImports(check.pkg)
 		}
 		// If the same package name was used by multiple packages, display the full path.
 		if len(check.pkgPathMap[pkg.name]) > 1 {
diff --git a/src/go/types/issues_test.go b/src/go/types/issues_test.go
index 44926919ef..51995af30a 100644
--- a/src/go/types/issues_test.go
+++ b/src/go/types/issues_test.go
@@ -577,42 +577,64 @@ func TestIssue44515(t *testing.T) {
 }
 
 func TestIssue43124(t *testing.T) {
-	// TODO(rFindley) enhance the testdata tests to be able to express this type
-	//                of setup.
+	// TODO(rFindley) move this to testdata by enhancing support for importing.
 
 	// All involved packages have the same name (template). Error messages should
 	// disambiguate between text/template and html/template by printing the full
 	// path.
 	const (
 		asrc = `package a; import "text/template"; func F(template.Template) {}; func G(int) {}`
-		bsrc = `package b; import ("a"; "html/template"); func _() { a.F(template.Template{}) }`
-		csrc = `package c; import ("a"; "html/template"); func _() { a.G(template.Template{}) }`
+		bsrc = `
+package b
+
+import (
+	"a"
+	"html/template"
+)
+
+func _() {
+	// Packages should be fully qualified when there is ambiguity within the
+	// error string itself.
+	a.F(template /* ERROR cannot use.*html/template.* as .*text/template */ .Template{})
+}
+`
+		csrc = `
+package c
+
+import (
+	"a"
+	"fmt"
+	"html/template"
+)
+
+// Issue #46905: make sure template is not the first package qualified.
+var _ fmt.Stringer = 1 // ERROR cannot use 1.*as fmt\.Stringer
+
+// Packages should be fully qualified when there is ambiguity in reachable
+// packages. In this case both a (and for that matter html/template) import
+// text/template.
+func _() { a.G(template /* ERROR cannot use .*html/template.*Template */ .Template{}) }
+`
+
+		tsrc = `
+package template
+
+import "text/template"
+
+type T int
+
+// Verify that the current package name also causes disambiguation.
+var _ T = template /* ERROR cannot use.*text/template.* as T value */.Template{}
+`
 	)
 
 	a, err := pkgFor("a", asrc, nil)
 	if err != nil {
 		t.Fatalf("package a failed to typecheck: %v", err)
 	}
-	conf := Config{Importer: importHelper{pkg: a, fallback: importer.Default()}}
-
-	// Packages should be fully qualified when there is ambiguity within the
-	// error string itself.
-	bast := mustParse(t, bsrc)
-	_, err = conf.Check(bast.Name.Name, fset, []*ast.File{bast}, nil)
-	if err == nil {
-		t.Fatal("package b had no errors")
-	}
-	if !strings.Contains(err.Error(), "text/template") || !strings.Contains(err.Error(), "html/template") {
-		t.Errorf("type checking error for b does not disambiguate package template: %q", err)
-	}
+	imp := importHelper{pkg: a, fallback: importer.Default()}
 
-	// ...and also when there is any ambiguity in reachable packages.
-	cast := mustParse(t, csrc)
-	_, err = conf.Check(cast.Name.Name, fset, []*ast.File{cast}, nil)
-	if err == nil {
-		t.Fatal("package c had no errors")
-	}
-	if !strings.Contains(err.Error(), "html/template") {
-		t.Errorf("type checking error for c does not disambiguate package template: %q", err)
-	}
+	testFiles(t, nil, []string{"b.go"}, [][]byte{[]byte(bsrc)}, false, imp)
+	testFiles(t, nil, []string{"c.go"}, [][]byte{[]byte(csrc)}, false, imp)
+	testFiles(t, nil, []string{"t.go"}, [][]byte{[]byte(tsrc)}, false, imp)
 }
diff --git a/src/go/types/testdata/check/issues.src b/src/go/types/testdata/check/issues.src
index 9d9fc7862f..b0231548a7 100644
--- a/src/go/types/testdata/check/issues.src
+++ b/src/go/types/testdata/check/issues.src
@@ -332,7 +332,7 @@ func issue28281g() (... /* ERROR can only use ... with final parameter */ TT)
 func issue26234a(f *syn.File) {
 	// The error message below should refer to the actual package name (syntax)
 	// not the local package name (syn).
-	f.foo /* ERROR f.foo undefined \(type \*syntax.File has no field or method foo\) */
+	f.foo /* ERROR f\.foo undefined \(type \*syntax\.File has no field or method foo\) */
 }
 
 type T struct {
@@ -361,7 +361,7 @@ func issue35895() {
 
 	// Because both t1 and t2 have the same global package name (template),
 	// qualify packages with full path name in this case.
-	var _ t1.Template = t2 /* ERROR cannot use .* \(value of type "html/template".Template\) as "text/template".Template */ .Template{}
+	var _ t1.Template = t2 /* ERROR cannot use .* \(value of type .html/template.\.Template\) as .text/template.\.Template */ .Template{}
 }
 
 func issue42989(s uint) {
diff --git a/src/go/types/testdata/examples/functions.go2 b/src/go/types/testdata/examples/functions.go2
index f15c709ce4..81b9d3456c 100644
--- a/src/go/types/testdata/examples/functions.go2
+++ b/src/go/types/testdata/examples/functions.go2
@@ -210,5 +210,5 @@ func _() {
 func h[] /* ERROR empty type parameter list */ ()
 
 func _() {
-	h[] /* ERROR operand */ ()
+	h /* ERROR cannot index */ [] /* ERROR operand */ ()
 }
diff --git a/src/go/types/testdata/fixedbugs/issue46403.src b/src/go/types/testdata/fixedbugs/issue46403.src
new file mode 100644
index 0000000000..9d475222ad
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue46403.src
@@ -0,0 +1,11 @@
+// Copyright 2021 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.
+
+package issue46403
+
+func _() {
+	// a should be used, despite the parser error below.
+	var a []int
+	var _ = a[] // ERROR expected operand
+}
diff --git a/src/go/types/testdata/fixedbugs/issue46404.go1 b/src/go/types/testdata/fixedbugs/issue46404.go1
new file mode 100644
index 0000000000..db604bc1ac
--- /dev/null
+++ b/src/go/types/testdata/fixedbugs/issue46404.go1
@@ -0,0 +1,8 @@
+// Copyright 2021 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.
+
+package issue46404
+
+// Check that we don't type check t[_] as an instantiation.
+type t [t /* ERROR not a type */ [_]]_ // ERROR cannot use
diff --git a/src/go/types/typexpr.go b/src/go/types/typexpr.go
index 97df908ae9..e6be7b72e4 100644
--- a/src/go/types/typexpr.go
+++ b/src/go/types/typexpr.go
@@ -262,8 +262,12 @@ func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
 		}
 
 	case *ast.IndexExpr:
-		exprs := typeparams.UnpackExpr(e.Index)
-		return check.instantiatedType(e.X, exprs, def)
+		if typeparams.Enabled {
+			exprs := typeparams.UnpackExpr(e.Index)
+			return check.instantiatedType(e.X, exprs, def)
+		}
+		check.errorf(e0, _NotAType, "%s is not a type", e0)
+		check.use(e.X)
 
 	case *ast.ParenExpr:
 		// Generic types must be instantiated before they can be used in any form.
diff --git a/src/internal/buildcfg/exp.go b/src/internal/buildcfg/exp.go
index e78f987999..e87b6221f1 100644
--- a/src/internal/buildcfg/exp.go
+++ b/src/internal/buildcfg/exp.go
@@ -18,7 +18,7 @@ import (
 //
 // (This is not necessarily the set of experiments the compiler itself
 // was built with.)
-var Experiment goexperiment.Flags = parseExperiments()
+var Experiment goexperiment.Flags = parseExperiments(GOARCH)
 
 var regabiSupported = GOARCH == "amd64" || GOARCH == "arm64"
 var regabiDeveloping = false
@@ -41,7 +41,7 @@ var experimentBaseline = goexperiment.Flags{
 // Note: must agree with runtime.framepointer_enabled.
 var FramePointerEnabled = GOARCH == "amd64" || GOARCH == "arm64"
 
-func parseExperiments() goexperiment.Flags {
+func parseExperiments(goarch string) goexperiment.Flags {
 	// Start with the statically enabled set of experiments.
 	flags := experimentBaseline
 
@@ -96,11 +96,11 @@ func parseExperiments() goexperiment.Flags {
 	}
 
 	// regabiwrappers is always enabled on amd64.
-	if GOARCH == "amd64" {
+	if goarch == "amd64" {
 		flags.RegabiWrappers = true
 	}
 	// regabi is only supported on amd64 and arm64.
-	if GOARCH != "amd64" && GOARCH != "arm64" {
+	if goarch != "amd64" && goarch != "arm64" {
 		flags.RegabiWrappers = false
 		flags.RegabiReflect = false
 		flags.RegabiArgs = false
@@ -161,3 +161,10 @@ func EnabledExperiments() []string {
 func AllExperiments() []string {
 	return expList(&Experiment, nil, true)
 }
+
+// UpdateExperiments updates the Experiment global based on a new GOARCH value.
+// This is only required for cmd/go, which can change GOARCH after
+// program startup due to use of "go env -w".
+func UpdateExperiments(goarch string) {
+	Experiment = parseExperiments(goarch)
+}
diff --git a/src/net/dial_test.go b/src/net/dial_test.go
index f899da10cf..723038c7a2 100644
--- a/src/net/dial_test.go
+++ b/src/net/dial_test.go
@@ -155,40 +155,27 @@ func slowDialTCP(ctx context.Context, network string, laddr, raddr *TCPAddr) (*T
 	return c, err
 }
 
-func dialClosedPort(t *testing.T) (actual, expected time.Duration) {
-	// Estimate the expected time for this platform.
-	// On Windows, dialing a closed port takes roughly 1 second,
-	// but other platforms should be instantaneous.
-	if runtime.GOOS == "windows" {
-		expected = 1500 * time.Millisecond
-	} else if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
-		expected = 150 * time.Millisecond
-	} else {
-		expected = 95 * time.Millisecond
-	}
+func dialClosedPort(t *testing.T) (dialLatency time.Duration) {
+	// On most platforms, dialing a closed port should be nearly instantaneous —
+	// less than a few hundred milliseconds. However, on some platforms it may be
+	// much slower: on Windows and OpenBSD, it has been observed to take up to a
+	// few seconds.
 
 	l, err := Listen("tcp", "127.0.0.1:0")
 	if err != nil {
-		t.Logf("dialClosedPort: Listen failed: %v", err)
-		return 999 * time.Hour, expected
+		t.Fatalf("dialClosedPort: Listen failed: %v", err)
 	}
 	addr := l.Addr().String()
 	l.Close()
-	// On OpenBSD, interference from TestTCPSelfConnect is mysteriously
-	// causing the first attempt to hang for a few seconds, so we throw
-	// away the first result and keep the second.
-	for i := 1; ; i++ {
-		startTime := time.Now()
-		c, err := Dial("tcp", addr)
-		if err == nil {
-			c.Close()
-		}
-		elapsed := time.Now().Sub(startTime)
-		if i == 2 {
-			t.Logf("dialClosedPort: measured delay %v", elapsed)
-			return elapsed, expected
-		}
+
+	startTime := time.Now()
+	c, err := Dial("tcp", addr)
+	if err == nil {
+		c.Close()
 	}
+	elapsed := time.Now().Sub(startTime)
+	t.Logf("dialClosedPort: measured delay %v", elapsed)
+	return elapsed
 }
 
 func TestDialParallel(t *testing.T) {
@@ -198,10 +185,7 @@ func TestDialParallel(t *testing.T) {
 		t.Skip("both IPv4 and IPv6 are required")
 	}
 
-	closedPortDelay, expectClosedPortDelay := dialClosedPort(t)
-	if closedPortDelay > expectClosedPortDelay {
-		t.Errorf("got %v; want <= %v", closedPortDelay, expectClosedPortDelay)
-	}
+	closedPortDelay := dialClosedPort(t)
 
 	const instant time.Duration = 0
 	const fallbackDelay = 200 * time.Millisecond
@@ -675,10 +659,7 @@ func TestDialerDualStack(t *testing.T) {
 		t.Skip("both IPv4 and IPv6 are required")
 	}
 
-	closedPortDelay, expectClosedPortDelay := dialClosedPort(t)
-	if closedPortDelay > expectClosedPortDelay {
-		t.Errorf("got %v; want <= %v", closedPortDelay, expectClosedPortDelay)
-	}
+	closedPortDelay := dialClosedPort(t)
 
 	origTestHookLookupIP := testHookLookupIP
 	defer func() { testHookLookupIP = origTestHookLookupIP }()
diff --git a/src/net/lookup_windows_test.go b/src/net/lookup_windows_test.go
index 62b61ed6c2..aa95501d02 100644
--- a/src/net/lookup_windows_test.go
+++ b/src/net/lookup_windows_test.go
@@ -299,7 +299,7 @@ func lookupPTR(name string) (ptr []string, err error) {
 	ptr = make([]string, 0, 10)
 	rx := regexp.MustCompile(`(?m)^Pinging\s+([a-zA-Z0-9.\-]+)\s+\[.*$`)
 	for _, ans := range rx.FindAllStringSubmatch(r, -1) {
-		ptr = append(ptr, ans[1]+".")
+		ptr = append(ptr, absDomainName([]byte(ans[1])))
 	}
 	return
 }
diff --git a/src/os/fifo_test.go b/src/os/fifo_test.go
index 9b262f8205..007ed29129 100644
--- a/src/os/fifo_test.go
+++ b/src/os/fifo_test.go
@@ -26,9 +26,6 @@ func TestFifoEOF(t *testing.T) {
 	switch runtime.GOOS {
 	case "android":
 		t.Skip("skipping on Android; mkfifo syscall not available")
-	case "openbsd":
-		// On OpenBSD 6.2 this test just hangs for some reason.
-		t.Skip("skipping on OpenBSD; issue 25877")
 	}
 
 	dir := t.TempDir()
diff --git a/src/reflect/value.go b/src/reflect/value.go
index 4341fd3f90..7589966e22 100644
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -1377,10 +1377,16 @@ func valueInterface(v Value, safe bool) interface{} {
 	return packEface(v)
 }
 
-// InterfaceData returns the interface v's value as a uintptr pair.
+// InterfaceData returns a pair of unspecified uintptr values.
 // It panics if v's Kind is not Interface.
+//
+// In earlier versions of Go, this function returned the interface's
+// value as a uintptr pair. As of Go 1.4, the implementation of
+// interface values precludes any defined use of InterfaceData.
+//
+// Deprecated: The memory representation of interface values is not
+// compatible with InterfaceData.
 func (v Value) InterfaceData() [2]uintptr {
-	// TODO: deprecate this
 	v.mustBe(Interface)
 	// We treat this as a read operation, so we allow
 	// it even for unexported data, because the caller
diff --git a/src/runtime/internal/atomic/atomic_386.s b/src/runtime/internal/atomic/atomic_386.s
index 37318e0ad7..724d515231 100644
--- a/src/runtime/internal/atomic/atomic_386.s
+++ b/src/runtime/internal/atomic/atomic_386.s
@@ -65,7 +65,7 @@ TEXT ·Xaddint64(SB), NOSPLIT, $0-20
 
 // bool ·Cas64(uint64 *val, uint64 old, uint64 new)
 // Atomically:
-//	if(*val == *old){
+//	if(*val == old){
 //		*val = new;
 //		return 1;
 //	} else {
diff --git a/src/time/format.go b/src/time/format.go
index 6040ed5aeb..bb173a21c2 100644
--- a/src/time/format.go
+++ b/src/time/format.go
@@ -751,8 +751,11 @@ type ParseError struct {
 
 // These are borrowed from unicode/utf8 and strconv and replicate behavior in
 // that package, since we can't take a dependency on either.
-const runeSelf = 0x80
-const lowerhex = "0123456789abcdef"
+const (
+	lowerhex  = "0123456789abcdef"
+	runeSelf  = 0x80
+	runeError = '\uFFFD'
+)
 
 func quote(s string) string {
 	buf := make([]byte, 1, len(s)+2) // slice will be at least len(s) + quotes
@@ -765,7 +768,16 @@ func quote(s string) string {
 			// reproduce strconv.Quote's behavior with full fidelity but
 			// given how rarely we expect to hit these edge cases, speed and
 			// conciseness are better.
-			for j := 0; j < len(string(c)) && j < len(s); j++ {
+			var width int
+			if c == runeError {
+				width = 1
+				if i+2 < len(s) && s[i:i+3] == string(runeError) {
+					width = 3
+				}
+			} else {
+				width = len(string(c))
+			}
+			for j := 0; j < width; j++ {
 				buf = append(buf, `\x`...)
 				buf = append(buf, lowerhex[s[i+j]>>4])
 				buf = append(buf, lowerhex[s[i+j]&0xF])
diff --git a/src/time/time_test.go b/src/time/time_test.go
index f272bbd558..cea5f2d3f5 100644
--- a/src/time/time_test.go
+++ b/src/time/time_test.go
@@ -917,6 +917,11 @@ var parseDurationErrorTests = []struct {
 	{".s", `".s"`},
 	{"+.s", `"+.s"`},
 	{"1d", `"1d"`},
+	{"\x85\x85", `"\x85\x85"`},
+	{"\xffff", `"\xffff"`},
+	{"hello \xffff world", `"hello \xffff world"`},
+	{"\uFFFD", `"\xef\xbf\xbd"`},                                             // utf8.RuneError
+	{"\uFFFD hello \uFFFD world", `"\xef\xbf\xbd hello \xef\xbf\xbd world"`}, // utf8.RuneError
 	// overflow
 	{"9223372036854775810ns", `"9223372036854775810ns"`},
 	{"9223372036854775808ns", `"9223372036854775808ns"`},
diff --git a/test/fixedbugs/issue46907.go b/test/fixedbugs/issue46907.go
new file mode 100644
index 0000000000..bd82f4f2b1
--- /dev/null
+++ b/test/fixedbugs/issue46907.go
@@ -0,0 +1,11 @@
+// compile
+
+// Copyright 2021 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.
+
+package p
+
+func f(b []byte) []byte {
+	return (*[32]byte)(b[:32])[:]
+}