cmd/go: handle escapes in pkg-config output

This commit also adds a test for pkg-config usage in cgo.

Fixes #16455.

Change-Id: I95fb6a288a4d19093c4613c93878017d95cbe4a2
Reviewed-on: https://go-review.googlesource.com/32735
Run-TryBot: Quentin Smith <quentin@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/build.go

@@ -1635,6 +1635,39 @@ func (b *builder) pkgconfigCmd() string {
 	return envList("PKG_CONFIG", defaultPkgConfig)[0]
 }
 
+// splitPkgConfigOutput parses the pkg-config output into a slice of
+// flags. pkg-config always uses \ to escape special characters.
+func splitPkgConfigOutput(out []byte) []string {
+	if len(out) == 0 {
+		return nil
+	}
+	var flags []string
+	flag := make([]byte, len(out))
+	r, w := 0, 0
+	for r < len(out) {
+		switch out[r] {
+		case ' ', '\t', '\r', '\n':
+			if w > 0 {
+				flags = append(flags, string(flag[:w]))
+			}
+			w = 0
+		case '\\':
+			r++
+			fallthrough
+		default:
+			if r < len(out) {
+				flag[w] = out[r]
+				w++
+			}
+		}
+		r++
+	}
+	if w > 0 {
+		flags = append(flags, string(flag[:w]))
+	}
+	return flags
+}
+
 // Calls pkg-config if needed and returns the cflags/ldflags needed to build the package.
 func (b *builder) getPkgConfigFlags(p *Package) (cflags, ldflags []string, err error) {
 	if pkgs := p.CgoPkgConfig; len(pkgs) > 0 {
@@ -1647,7 +1680,7 @@ func (b *builder) getPkgConfigFlags(p *Package) (cflags, ldflags []string, err e
 			return
 		}
 		if len(out) > 0 {
-			cflags = strings.Fields(string(out))
+			cflags = splitPkgConfigOutput(out)
 		}
 		out, err = b.runOut(p.Dir, p.ImportPath, nil, b.pkgconfigCmd(), "--libs", pkgs)
 		if err != nil {

src/cmd/go/build_test.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"os"
+	"reflect"
 	"testing"
 )
 
@@ -23,3 +24,21 @@ func TestRemoveDevNull(t *testing.T) {
 		t.Errorf("mayberemovefile(%s) did remove it; oops", os.DevNull)
 	}
 }
+
+func TestSplitPkgConfigOutput(t *testing.T) {
+	for _, test := range []struct {
+		in   []byte
+		want []string
+	}{
+		{[]byte(`-r:foo -L/usr/white\ space/lib -lfoo\ bar -lbar\ baz`), []string{"-r:foo", "-L/usr/white space/lib", "-lfoo bar", "-lbar baz"}},
+		{[]byte(`-lextra\ fun\ arg\\`), []string{`-lextra fun arg\`}},
+		{[]byte(`broken flag\`), []string{"broken", "flag"}},
+		{[]byte("\textra     whitespace\r\n"), []string{"extra", "whitespace"}},
+		{[]byte("     \r\n      "), nil},
+	} {
+		got := splitPkgConfigOutput(test.in)
+		if !reflect.DeepEqual(got, test.want) {
+			t.Errorf("splitPkgConfigOutput(%v) = %v; want %v", test.in, got, test.want)
+		}
+	}
+}

src/cmd/go/go_test.go

@@ -2201,6 +2201,51 @@ func TestCgoHandlesWlORIGIN(t *testing.T) {
 	tg.run("build", "origin")
 }
 
+func TestCgoPkgConfig(t *testing.T) {
+	if !canCgo {
+		t.Skip("skipping because cgo not enabled")
+	}
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+
+	tg.run("env", "PKG_CONFIG")
+	if _, err := exec.LookPath(strings.TrimSpace(tg.getStdout())); err != nil {
+		t.Skip("skipping because pkg-config could not be found")
+	}
+
+	// OpenBSD's pkg-config is strict about whitespace and only
+	// supports backslash-escaped whitespace. It does not support
+	// quotes, which the normal freedesktop.org pkg-config does
+	// support. See http://man.openbsd.org/pkg-config.1
+	tg.tempFile("foo.pc", `
+Name: foo
+Description: The foo library
+Version: 1.0.0
+Cflags: -Dhello=10 -Dworld=+32 -DDEFINED_FROM_PKG_CONFIG=hello\ world
+`)
+	tg.tempFile("foo.go", `package main
+
+/*
+#cgo pkg-config: foo
+int value() {
+	return DEFINED_FROM_PKG_CONFIG;
+}
+*/
+import "C"
+import "os"
+
+func main() {
+	if C.value() != 42 {
+		println("value() =", C.value(), "wanted 42")
+		os.Exit(1)
+	}
+}
+`)
+	tg.setenv("PKG_CONFIG_PATH", tg.path("."))
+	tg.run("run", tg.path("foo.go"))
+}
+
 // "go test -c -test.bench=XXX errors" should not hang
 func TestIssue6480(t *testing.T) {
 	tg := testgo(t)