[release-branch.go1.9] cmd/go: permit pkg-config flags in any argument position

Fixes #23875

Change-Id: I503af71f44d11cd6b787fef100246b55735614a0
Reviewed-on: https://go-review.googlesource.com/94896
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/103155
Run-TryBot: Andrew Bonventre <andybons@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 45 insertions, 4 deletions

diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index 28c2bc147a..03d29609a9 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -4496,3 +4496,36 @@ func TestBadCgoDirectives(t *testing.T) {
 	tg.run("build", "-n", "x")
 	tg.grepStderr("-D@foo", "did not find -D@foo in commands")
 }
+
+func TestTwoPkgConfigs(t *testing.T) {
+	if !canCgo {
+		t.Skip("no cgo")
+	}
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		t.Skipf("no shell scripts on %s", runtime.GOOS)
+	}
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.tempFile("src/x/a.go", `package x
+		// #cgo pkg-config: --static a
+		import "C"
+	`)
+	tg.tempFile("src/x/b.go", `package x
+		// #cgo pkg-config: --static a
+		import "C"
+	`)
+	tg.tempFile("pkg-config.sh", `#!/bin/sh
+echo $* >>`+tg.path("pkg-config.out"))
+	tg.must(os.Chmod(tg.path("pkg-config.sh"), 0755))
+	tg.setenv("GOPATH", tg.path("."))
+	tg.setenv("PKG_CONFIG", tg.path("pkg-config.sh"))
+	tg.run("build", "x")
+	out, err := ioutil.ReadFile(tg.path("pkg-config.out"))
+	tg.must(err)
+	out = bytes.TrimSpace(out)
+	want := "--cflags --static --static -- a a\n--libs --static --static -- a a"
+	if !bytes.Equal(out, []byte(want)) {
+		t.Errorf("got %q want %q", out, want)
+	}
+}
diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 23946e466b..e931629105 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/src/cmd/go/internal/work/build.go
@@ -1525,11 +1525,19 @@ func splitPkgConfigOutput(out []byte) []string {
 
 // Calls pkg-config if needed and returns the cflags/ldflags needed to build the package.
 func (b *Builder) getPkgConfigFlags(p *load.Package) (cflags, ldflags []string, err error) {
-	if pkgs := p.CgoPkgConfig; len(pkgs) > 0 {
+	if pcargs := p.CgoPkgConfig; len(pcargs) > 0 {
+		// pkg-config permits arguments to appear anywhere in
+		// the command line. Move them all to the front, before --.
 		var pcflags []string
-		for len(pkgs) > 0 && strings.HasPrefix(pkgs[0], "--") {
-			pcflags = append(pcflags, pkgs[0])
-			pkgs = pkgs[1:]
+		var pkgs []string
+		for _, pcarg := range pcargs {
+			if pcarg == "--" {
+				// We're going to add our own "--" argument.
+			} else if strings.HasPrefix(pcarg, "--") {
+				pcflags = append(pcflags, pcarg)
+			} else {
+				pkgs = append(pkgs, pcarg)
+			}
 		}
 		for _, pkg := range pkgs {
 			if !load.SafeArg(pkg) {