cmd/go: fix -gcflags, -ldflags not applying to current directory

A flag setting like -gcflags=-e applies only to the packages
named on the command line, not to their dependencies.
The way we used to implement this was to remember the
command line arguments, reinterpret them as pattern matches
instead of package argument generators (globs), and apply them
during package load. The reason for this complexity was to
address a command-line like:

	go build -gcflags=-e fmt runtime

The load of fmt will load dependencies, including runtime,
and the load of runtime will reuse the result of the earlier load.
Because we were computing the effective -gcflags for each
package during the load, we had to have a way to tell, when
encountering runtime during the load of fmt, that runtime had
been named on the command line, even though we hadn't
gotten that far. That would be easy if the only possible
arguments were import paths, but we also need to handle

	go build -gcflags=-e fmt runt...
	go build -gcflags=-e fmt $GOROOT/src/runtime
	go build -gcflags=-e fmt $GOROOT/src/runt...
	and so on.

The match predicates usually did their job well, but not
always. In particular, thanks to symlinks and case-insensitive
file systems and unusual ways to spell file paths, it's always
been possible in various corner cases to give an argument
that evalutes to the runtime package during loading but
failed to match it when reused to determine "was this package
named on the command line?"

CL 109235 fixed one instance of this problem by making
a directory pattern match case-insensitive on Windows, but that
is incorrect in some other cases and doesn't address the root problem,
namely that there will probably always be odd corner cases
where pattern matching and pattern globbing are not exactly aligned.

This CL eliminates the assumption that pattern matching
and pattern globbing are always completely in agreement,
by simply marking the packages named on the command line
after the package load returns them. This means delaying
the computation of tool flags until after the load too,
for a few different ways packages are loaded.
The different load entry points add some complexity,
which is why the original approach seemed more attractive,
but the original approach had complexity that we simply
didn't recognize at the time.

This CL then rolls back the CL 109235 pattern-matching change,
but it keeps the test introduced in that CL. That test still passes.

In addition to fixing ambiguity due to case-sensitive file systems,
this new approach also very likely fixes various ambiguities that
might arise from abuse of symbolic links.

Fixes #24232.
Fixes #24456.
Fixes #24750.
Fixes #25046.
Fixes #25878.

Change-Id: I0b09825785dfb5112fb11494cff8527ebf57966f
Reviewed-on: https://go-review.googlesource.com/129059
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

6 files changed, 128 insertions, 117 deletions

diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index a7be617af9..3ca50bb475 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -5648,37 +5648,6 @@ 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 47953f09a4..e4148bceb0 100644
--- a/src/cmd/go/internal/get/get.go
+++ b/src/cmd/go/internal/get/get.go
@@ -240,7 +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)
 	}
@@ -329,7 +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/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 3a3a38651c..b7257e77e3 100644
--- a/src/cmd/go/internal/load/pkg.go
+++ b/src/cmd/go/internal/load/pkg.go
@@ -374,15 +374,17 @@ 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 +433,9 @@ 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()
@@ -1185,27 +1190,6 @@ 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 +1724,31 @@ 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) {
@@ -1843,7 +1847,14 @@ func PackagesAndErrors(patterns []string) []*Package {
 
 	for _, m := range matches {
 		for _, pkg := range m.Pkgs {
-			p := LoadPackage(pkg, &stk)
+			p := loadPackage(pkg, &stk)
+			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
 			}
@@ -1852,9 +1863,24 @@ func PackagesAndErrors(patterns []string) []*Package {
 		}
 	}
 
+	// 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 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)
@@ -1986,5 +2012,7 @@ 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/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() {}