cmd/go, go/build: ignore vendor directories with no Go source files

Otherwise it is impossible to vendor a/b/c without hiding the real a/b.
I also updated golang.org/s/go15vendor.

Fixes #13832.

Change-Id: Iee3d53c11ea870721803f6e8e67845b405686e79
Reviewed-on: https://go-review.googlesource.com/18644Reviewed-by: Andrew Gerrand <adg@golang.org>

src/cmd/go/pkg.go

@@ -420,7 +420,7 @@ func vendoredImportPath(parent *Package, path string) (found string) {
 			continue
 		}
 		targ := filepath.Join(dir[:i], vpath)
-		if isDir(targ) {
+		if isDir(targ) && hasGoFiles(targ) {
 			// We started with parent's dir c:\gopath\src\foo\bar\baz\quux\xyzzy.
 			// We know the import path for parent's dir.
 			// We chopped off some number of path elements and
@@ -443,6 +443,20 @@ func vendoredImportPath(parent *Package, path string) (found string) {
 	return path
 }
 
+// hasGoFiles reports whether dir contains any files with names ending in .go.
+// For a vendor check we must exclude directories that contain no .go files.
+// Otherwise it is not possible to vendor just a/b/c and still import the
+// non-vendored a/b. See golang.org/issue/13832.
+func hasGoFiles(dir string) bool {
+	fis, _ := ioutil.ReadDir(dir)
+	for _, fi := range fis {
+		if !fi.IsDir() && strings.HasSuffix(fi.Name(), ".go") {
+			return true
+		}
+	}
+	return false
+}
+
 // reusePackage reuses package p to satisfy the import at the top
 // of the import stack stk.  If this use causes an import loop,
 // reusePackage updates p's error information to record the loop.

src/cmd/go/testdata/src/vend/dir1/dir1.go

+package dir1

src/cmd/go/testdata/src/vend/vendor/vend/dir1/dir2/dir2.go

+package dir2

src/cmd/go/testdata/src/vend/x/x.go

@@ -3,3 +3,5 @@ package x
 import _ "p"
 import _ "q"
 import _ "r"
+import _ "vend/dir1"      // not vendored
+import _ "vend/dir1/dir2" // vendored

src/cmd/go/vendor_test.go

@@ -24,12 +24,14 @@ func TestVendorImports(t *testing.T) {
 	tg.run("list", "-f", "{{.ImportPath}} {{.Imports}}", "vend/...")
 	want := `
 		vend [vend/vendor/p r]
+		vend/dir1 []
 		vend/hello [fmt vend/vendor/strings]
 		vend/subdir [vend/vendor/p r]
 		vend/vendor/p []
 		vend/vendor/q []
 		vend/vendor/strings []
-		vend/x [vend/x/vendor/p vend/vendor/q vend/x/vendor/r]
+		vend/vendor/vend/dir1/dir2 []
+		vend/x [vend/x/vendor/p vend/vendor/q vend/x/vendor/r vend/dir1 vend/vendor/vend/dir1/dir2]
 		vend/x/invalid [vend/x/invalid/vendor/foo]
 		vend/x/vendor/p []
 		vend/x/vendor/p/p [notfound]
@@ -45,6 +47,14 @@ func TestVendorImports(t *testing.T) {
 	}
 }
 
+func TestVendorBuild(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
+	tg.setenv("GO15VENDOREXPERIMENT", "1")
+	tg.run("build", "vend/x")
+}
+
 func TestVendorRun(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()

src/go/build/build.go

@@ -583,7 +583,7 @@ func (ctxt *Context) Import(path string, srcDir string, mode ImportMode) (*Packa
 					vendor := ctxt.joinPath(root, sub, "vendor")
 					if ctxt.isDir(vendor) {
 						dir := ctxt.joinPath(vendor, path)
-						if ctxt.isDir(dir) {
+						if ctxt.isDir(dir) && hasGoFiles(ctxt, dir) {
 							p.Dir = dir
 							p.ImportPath = strings.TrimPrefix(pathpkg.Join(sub, "vendor", path), "src/")
 							p.Goroot = isGoroot
@@ -884,6 +884,20 @@ Found:
 	return p, pkgerr
 }
 
+// hasGoFiles reports whether dir contains any files with names ending in .go.
+// For a vendor check we must exclude directories that contain no .go files.
+// Otherwise it is not possible to vendor just a/b/c and still import the
+// non-vendored a/b. See golang.org/issue/13832.
+func hasGoFiles(ctxt *Context, dir string) bool {
+	ents, _ := ctxt.readDir(dir)
+	for _, ent := range ents {
+		if !ent.IsDir() && strings.HasSuffix(ent.Name(), ".go") {
+			return true
+		}
+	}
+	return false
+}
+
 func findImportComment(data []byte) (s string, line int) {
 	// expect keyword package
 	word, data := parseWord(data)

src/go/build/build_test.go

@@ -327,3 +327,21 @@ func TestImportVendorFailure(t *testing.T) {
 		t.Fatalf("error on failed import does not mention GOROOT/src/vendor directory:\n%s", e)
 	}
 }
+
+func TestImportVendorParentFailure(t *testing.T) {
+	testenv.MustHaveGoBuild(t) // really must just have source
+	ctxt := Default
+	ctxt.GOPATH = ""
+	// This import should fail because the vendor/golang.org/x/net/http2 directory has no source code.
+	p, err := ctxt.Import("golang.org/x/net/http2", filepath.Join(ctxt.GOROOT, "src/net/http"), 0)
+	if err == nil {
+		t.Fatalf("found empty parent in %s", p.Dir)
+	}
+	if p != nil && p.Dir != "" {
+		t.Fatalf("decided to use %s", p.Dir)
+	}
+	e := err.Error()
+	if !strings.Contains(e, " (vendor tree)") {
+		t.Fatalf("error on failed import does not mention GOROOT/src/vendor directory:\n%s", e)
+	}
+}