cmd/internal/moddeps: use filepath.SkipDir only on directories

If a filepath.WalkFunc returns filepath.SkipDir when invoked on a
non-directory file, it skips the remaining files in the containing
directory.¹

CL 276272 accidentally added a code path that triggers this behavior
whenever filepath.Walk reaches a non-directory file that begins with
a dot, such as .gitattributes or .DS_Store, causing findGorootModules
to return early without finding any modules in GOROOT. Tests that use
it ceased to provide test coverage that the tree is tidy.

Add an explicit check for info.IsDir in the 5 places that intend to
use filepath.SkipDir to skip traversing that directory. Even paths
like GOROOT/bin and GOROOT/pkg which are unlikely to be anything but
a directory are worth checking, since the goal of moddeps is to take
a possibly problematic GOROOT tree as input and detect problems.

While the goal of findGorootModules is to find all modules in GOROOT
programmatically (in case new modules are added or modified), there
are 4 modules now that are quite likely to exist, so check for their
presence to avoid similar regressions. (It's not hard to update this
test if a well-known GOROOT module is removed or otherwise modified;
but if it becomes hard we can simplify it to check for a reasonable
number of modules instead.)

Also fix the minor skew that has crept in since the test got disabled.

¹ This wasn't necessarily an intentional design decision, but it was
  found only when Go 1.4 was already out. See CL 11690 for details.

Fixes #46254.

Change-Id: Id55ed926f8c0094b1af923070de72bacca05996f
Reviewed-on: https://go-review.googlesource.com/c/go/+/320991
Trust: Dmitri Shuralyov <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
Reviewed-by: Filippo Valsorda <[email protected]>

Author: dmitshur

src/cmd/internal/moddeps/moddeps_test.go

@@ -227,7 +227,7 @@ func makeGOROOTCopy(t *testing.T) string {
 		if err != nil {
 			return err
 		}
-		if src == filepath.Join(runtime.GOROOT(), ".git") {
+		if info.IsDir() && src == filepath.Join(runtime.GOROOT(), ".git") {
 			return filepath.SkipDir
 		}
 
@@ -237,9 +237,8 @@ func makeGOROOTCopy(t *testing.T) string {
 		}
 		dst := filepath.Join(gorootCopyDir, rel)
 
-		switch src {
-		case filepath.Join(runtime.GOROOT(), "bin"),
-			filepath.Join(runtime.GOROOT(), "pkg"):
+		if info.IsDir() && (src == filepath.Join(runtime.GOROOT(), "bin") ||
+			src == filepath.Join(runtime.GOROOT(), "pkg")) {
 			// If the OS supports symlinks, use them instead
 			// of copying the bin and pkg directories.
 			if err := os.Symlink(src, dst); err == nil {
@@ -414,15 +413,15 @@ func findGorootModules(t *testing.T) []gorootModule {
 			if info.IsDir() && (info.Name() == "vendor" || info.Name() == "testdata") {
 				return filepath.SkipDir
 			}
-			if path == filepath.Join(runtime.GOROOT(), "pkg") {
+			if info.IsDir() && path == filepath.Join(runtime.GOROOT(), "pkg") {
 				// GOROOT/pkg contains generated artifacts, not source code.
 				//
 				// In https://golang.org/issue/37929 it was observed to somehow contain
 				// a module cache, so it is important to skip. (That helps with the
 				// running time of this test anyway.)
 				return filepath.SkipDir
 			}
-			if strings.HasPrefix(info.Name(), "_") || strings.HasPrefix(info.Name(), ".") {
+			if info.IsDir() && (strings.HasPrefix(info.Name(), "_") || strings.HasPrefix(info.Name(), ".")) {
 				// _ and . prefixed directories can be used for internal modules
 				// without a vendor directory that don't contribute to the build
 				// but might be used for example as code generators.
@@ -457,8 +456,31 @@ func findGorootModules(t *testing.T) []gorootModule {
 			goroot.modules = append(goroot.modules, m)
 			return nil
 		})
-	})
+		if goroot.err != nil {
+			return
+		}
 
+		// knownGOROOTModules is a hard-coded list of modules that are known to exist in GOROOT.
+		// If findGorootModules doesn't find a module, it won't be covered by tests at all,
+		// so make sure at least these modules are found. See issue 46254. If this list
+		// becomes a nuisance to update, can be replaced with len(goroot.modules) check.
+		knownGOROOTModules := [...]string{
+			"std",
+			"cmd",
+			"misc",
+			"test/bench/go1",
+		}
+		var seen = make(map[string]bool) // Key is module path.
+		for _, m := range goroot.modules {
+			seen[m.Path] = true
+		}
+		for _, m := range knownGOROOTModules {
+			if !seen[m] {
+				goroot.err = fmt.Errorf("findGorootModules didn't find the well-known module %q", m)
+				break
+			}
+		}
+	})
 	if goroot.err != nil {
 		t.Fatal(goroot.err)
 	}

src/go.mod

@@ -5,6 +5,6 @@ go 1.17
 require (
 	golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e
 	golang.org/x/net v0.0.0-20210510120150-4163338589ed
-	golang.org/x/sys v0.0.0-20210503173754-0981d6026fa6 // indirect
+	golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744 // indirect
 	golang.org/x/text v0.3.7-0.20210503195748-5c7c50ebbd4f // indirect
 )

src/go.sum

@@ -2,7 +2,7 @@ golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e h1:8foAy0aoO5GkqCvAEJ4VC4
 golang.org/x/crypto v0.0.0-20210503195802-e9a32991a82e/go.mod h1:P+XmwS30IXTQdn5tA2iutPOUgjI07+tq3H3K9MVA1s8=
 golang.org/x/net v0.0.0-20210510120150-4163338589ed h1:p9UgmWI9wKpfYmgaV/IZKGdXc5qEK45tDwwwDyjS26I=
 golang.org/x/net v0.0.0-20210510120150-4163338589ed/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
-golang.org/x/sys v0.0.0-20210503173754-0981d6026fa6 h1:cdsMqa2nXzqlgs183pHxtvoVwU7CyzaCTAUOg94af4c=
-golang.org/x/sys v0.0.0-20210503173754-0981d6026fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744 h1:yhBbb4IRs2HS9PPlAg6DMC6mUOKexJBNsLf4Z+6En1Q=
+golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/text v0.3.7-0.20210503195748-5c7c50ebbd4f h1:yQJrRE0hDxDFmZLlRaw+3vusO4fwNHgHIjUOMO7bHYI=
 golang.org/x/text v0.3.7-0.20210503195748-5c7c50ebbd4f/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=

src/net/http/h2_bundle.go

@@ -18,7 +18,7 @@ golang.org/x/net/idna
 golang.org/x/net/lif
 golang.org/x/net/nettest
 golang.org/x/net/route
-# golang.org/x/sys v0.0.0-20210503173754-0981d6026fa6
+# golang.org/x/sys v0.0.0-20210511113859-b0526f3d8744
 ## explicit; go 1.17
 golang.org/x/sys/cpu
 # golang.org/x/text v0.3.7-0.20210503195748-5c7c50ebbd4f