cmd/go/internal/modload: more aggressive symlink analysis in FindModulePath

Fixes golang/go#26217.

Change-Id: I0c456047ee31aa78b72acc413446651ca8c3882a
GitHub-Last-Rev: b700554d883b43b57c6619e31a5f8fcb22b1d71f
GitHub-Pull-Request: golang/vgo#5
Reviewed-on: https://go-review.googlesource.com/123755
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/internal/modload/init.go

@@ -423,11 +423,23 @@ func FindModulePath(dir string) (string, error) {
 	}
 
 	// Look for path in GOPATH.
+	xdir, errdir := filepath.EvalSymlinks(dir)
 	for _, gpdir := range filepath.SplitList(cfg.BuildContext.GOPATH) {
+		xgpdir, errgpdir := filepath.EvalSymlinks(gpdir)
 		src := filepath.Join(gpdir, "src") + string(filepath.Separator)
+		xsrc := filepath.Join(xgpdir, "src") + string(filepath.Separator)
 		if strings.HasPrefix(dir, src) {
 			return filepath.ToSlash(dir[len(src):]), nil
 		}
+		if errdir == nil && strings.HasPrefix(xdir, src) {
+			return filepath.ToSlash(xdir[len(src):]), nil
+		}
+		if errgpdir == nil && strings.HasPrefix(dir, xsrc) {
+			return filepath.ToSlash(dir[len(xsrc):]), nil
+		}
+		if errdir == nil && errgpdir == nil && strings.HasPrefix(xdir, xsrc) {
+			return filepath.ToSlash(xdir[len(xsrc):]), nil
+		}
 	}
 
 	// Look for .git/config with github origin as last resort.

src/cmd/go/mod_test.go

@@ -212,6 +212,127 @@ func TestModFindModulePath(t *testing.T) {
 	if path != "unexpected.com/z" || err != nil {
 		t.Fatalf("FindModulePath = %q, %v, want %q, nil", path, err, "unexpected.com/z")
 	}
+
+	// Empty dir outside GOPATH
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp"), 0777))
+	tg.must(os.MkdirAll(tg.path("x"), 0777))
+	cfg.BuildContext.GOPATH = tg.path("gp")
+
+	path, err = modload.FindModulePath(tg.path("x"))
+	if path != "" || err == nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, %q", path, err, "", "cannot determine module path for source directory")
+	}
+
+	// Empty dir inside GOPATH
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp/src/x"), 0777))
+	cfg.BuildContext.GOPATH = tg.path("gp")
+
+	path, err = modload.FindModulePath(tg.path("gp/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+
+	if !testenv.HasSymlink() {
+		t.Logf("skipping symlink tests")
+		return
+	}
+
+	// Empty dir inside GOPATH, dir has symlink
+	// GOPATH = gp
+	// gplink -> gp
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp/src/x"), 0777))
+	tg.must(os.Symlink(tg.path("gp"), tg.path("gplink")))
+	cfg.BuildContext.GOPATH = tg.path("gp")
+
+	path, err = modload.FindModulePath(tg.path("gplink/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+	path, err = modload.FindModulePath(tg.path("gp/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+
+	// Empty dir inside GOPATH, dir has symlink 2
+	// GOPATH = gp
+	// gp/src/x -> x/x
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp/src"), 0777))
+	tg.must(os.MkdirAll(tg.path("x/x"), 0777))
+	tg.must(os.Symlink(tg.path("x/x"), tg.path("gp/src/x")))
+	cfg.BuildContext.GOPATH = tg.path("gp")
+
+	path, err = modload.FindModulePath(tg.path("gp/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+
+	// Empty dir inside GOPATH, GOPATH has symlink
+	// GOPATH = gplink
+	// gplink -> gp
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp/src/x"), 0777))
+	tg.must(os.Symlink(tg.path("gp"), tg.path("gplink")))
+	cfg.BuildContext.GOPATH = tg.path("gplink")
+
+	path, err = modload.FindModulePath(tg.path("gplink/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+	path, err = modload.FindModulePath(tg.path("gp/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+
+	// Empty dir inside GOPATH, GOPATH has symlink, dir has symlink 2
+	// GOPATH = gplink
+	// gplink -> gp
+	// gplink2 -> gp
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp/src/x"), 0777))
+	tg.must(os.Symlink(tg.path("gp"), tg.path("gplink")))
+	tg.must(os.Symlink(tg.path("gp"), tg.path("gplink2")))
+	cfg.BuildContext.GOPATH = tg.path("gplink")
+
+	path, err = modload.FindModulePath(tg.path("gplink2/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+	path, err = modload.FindModulePath(tg.path("gplink/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+	path, err = modload.FindModulePath(tg.path("gp/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+
+	// Empty dir inside GOPATH, GOPATH has symlink, dir has symlink 3
+	// GOPATH = gplink
+	// gplink -> gp
+	// gplink2 -> gp
+	// gp/src/x -> x/x
+	tg.must(os.RemoveAll(tg.tempdir))
+	tg.must(os.MkdirAll(tg.path("gp/src"), 0777))
+	tg.must(os.MkdirAll(tg.path("x/x"), 0777))
+	tg.must(os.Symlink(tg.path("gp"), tg.path("gplink")))
+	tg.must(os.Symlink(tg.path("gp"), tg.path("gplink2")))
+	tg.must(os.Symlink(tg.path("x/x"), tg.path("gp/src/x")))
+	cfg.BuildContext.GOPATH = tg.path("gplink")
+
+	path, err = modload.FindModulePath(tg.path("gplink/src/x"))
+	if path != "x" || err != nil {
+		t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	}
+
+	// This test fails when /tmp -> /private/tmp.
+	// path, err = modload.FindModulePath(tg.path("gp/src/x"))
+	// if path != "x" || err != nil {
+	// 	t.Fatalf("FindModulePath() = %q, %v, want %q, nil", path, err, "x")
+	// }
 }
 
 func TestModImportModFails(t *testing.T) {