cmd/go: restore support for git submodules and update docs

Fixes #16165

Change-Id: Ic90e5873e0c8ee044f09543177192dcae1dcdbed
Reviewed-on: https://go-review.googlesource.com/24531
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/alldocs.go

@@ -508,8 +508,7 @@
 // searches for a branch or tag named "go1". If no such version exists it
 // retrieves the most recent version of the package.
 //
-// Unless vendoring support is disabled (see 'go help gopath'),
-// when go get checks out or updates a Git repository,
+// When go get checks out or updates a Git repository,
 // it also updates any git submodules referenced by the repository.
 //
 // Get never checks out or updates code stored in vendor directories.
@@ -1271,10 +1270,9 @@
 // let package authors make sure the custom import path is used and not a
 // direct path to the underlying code hosting site.
 //
-// If vendoring is enabled (see 'go help gopath'), then import path checking is
-// disabled for code found within vendor trees. This makes it possible to copy
-// code into alternate locations in vendor trees without needing to update import
-// comments.
+// Import path checking is disabled for code found within vendor trees.
+// This makes it possible to copy code into alternate locations in vendor trees
+// without needing to update import comments.
 //
 // See https://golang.org/s/go14customimport for details.
 //

src/cmd/go/get.go

@@ -55,8 +55,7 @@ rule is that if the local installation is running version "go1", get
 searches for a branch or tag named "go1". If no such version exists it
 retrieves the most recent version of the package.
 
-Unless vendoring support is disabled (see 'go help gopath'),
-when go get checks out or updates a Git repository,
+When go get checks out or updates a Git repository,
 it also updates any git submodules referenced by the repository.
 
 Get never checks out or updates code stored in vendor directories.

src/cmd/go/go_test.go

@@ -489,6 +489,16 @@ func (tg *testgoData) path(name string) string {
 	return filepath.Join(tg.tempdir, name)
 }
 
+// mustExist fails if path does not exist.
+func (tg *testgoData) mustExist(path string) {
+	if _, err := os.Stat(path); err != nil {
+		if os.IsNotExist(err) {
+			tg.t.Fatalf("%s does not exist but should", path)
+		}
+		tg.t.Fatalf("%s stat failed: %v", path, err)
+	}
+}
+
 // mustNotExist fails if path exists.
 func (tg *testgoData) mustNotExist(path string) {
 	if _, err := os.Stat(path); err == nil || !os.IsNotExist(err) {

src/cmd/go/help.go

@@ -261,10 +261,9 @@ unless it is being referred to by that import path. In this way, import comments
 let package authors make sure the custom import path is used and not a
 direct path to the underlying code hosting site.
 
-If vendoring is enabled (see 'go help gopath'), then import path checking is
-disabled for code found within vendor trees. This makes it possible to copy
-code into alternate locations in vendor trees without needing to update import
-comments.
+Import path checking is disabled for code found within vendor trees.
+This makes it possible to copy code into alternate locations in vendor trees
+without needing to update import comments.
 
 See https://golang.org/s/go14customimport for details.
 	`,

src/cmd/go/vcs.go

@@ -383,9 +383,6 @@ func (v *vcsCmd) ping(scheme, repo string) error {
 // The parent of dir must exist; dir must not.
 func (v *vcsCmd) create(dir, repo string) error {
 	for _, cmd := range v.createCmd {
-		if strings.Contains(cmd, "submodule") {
-			continue
-		}
 		if err := v.run(".", cmd, "dir", dir, "repo", repo); err != nil {
 			return err
 		}
@@ -396,9 +393,6 @@ func (v *vcsCmd) create(dir, repo string) error {
 // download downloads any new changes for the repo in dir.
 func (v *vcsCmd) download(dir string) error {
 	for _, cmd := range v.downloadCmd {
-		if strings.Contains(cmd, "submodule") {
-			continue
-		}
 		if err := v.run(dir, cmd); err != nil {
 			return err
 		}
@@ -445,9 +439,6 @@ func (v *vcsCmd) tagSync(dir, tag string) error {
 
 	if tag == "" && v.tagSyncDefault != nil {
 		for _, cmd := range v.tagSyncDefault {
-			if strings.Contains(cmd, "submodule") {
-				continue
-			}
 			if err := v.run(dir, cmd); err != nil {
 				return err
 			}
@@ -456,9 +447,6 @@ func (v *vcsCmd) tagSync(dir, tag string) error {
 	}
 
 	for _, cmd := range v.tagSyncCmd {
-		if strings.Contains(cmd, "submodule") {
-			continue
-		}
 		if err := v.run(dir, cmd, "tag", tag); err != nil {
 			return err
 		}

src/cmd/go/vendor_test.go

@@ -197,6 +197,7 @@ func TestGetSubmodules(t *testing.T) {
 	tg.setenv("GOPATH", tg.path("."))
 	tg.run("get", "-d", "github.com/rsc/go-get-issue-12612")
 	tg.run("get", "-u", "-d", "github.com/rsc/go-get-issue-12612")
+	tg.mustExist(tg.path("src/github.com/rsc/go-get-issue-12612/vendor/golang.org/x/crypto/.git"))
 }
 
 func TestVendorCache(t *testing.T) {