cmd/go, embed: exclude .* and _* from embedded directory trees

Discussion on #42328 led to a decision to exclude files matching
.* and _* from embedded directory results when embedding an
entire directory tree.

This CL implements that new behavior.

Fixes #42328.

Change-Id: I6188994e96348b3449c7d9d3d0d181cfbf2d4db1
Reviewed-on: https://go-review.googlesource.com/c/go/+/275092
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/load/pkg.go

@@ -1998,6 +1998,16 @@ func (p *Package) resolveEmbed(patterns []string) (files []string, pmap map[stri
 						return err
 					}
 					rel := filepath.ToSlash(path[len(p.Dir)+1:])
+					name := info.Name()
+					if path != file && (isBadEmbedName(name) || name[0] == '.' || name[0] == '_') {
+						// Ignore bad names, assuming they won't go into modules.
+						// Also avoid hidden files that user may not know about.
+						// See golang.org/issue/42328.
+						if info.IsDir() {
+							return fs.SkipDir
+						}
+						return nil
+					}
 					if info.IsDir() {
 						if _, err := fsys.Stat(filepath.Join(path, "go.mod")); err == nil {
 							return filepath.SkipDir
@@ -2007,10 +2017,6 @@ func (p *Package) resolveEmbed(patterns []string) (files []string, pmap map[stri
 					if !info.Mode().IsRegular() {
 						return nil
 					}
-					if isBadEmbedName(info.Name()) {
-						// Ignore bad names, assuming they won't go into modules.
-						return nil
-					}
 					count++
 					if have[rel] != pid {
 						have[rel] = pid
@@ -2050,6 +2056,9 @@ func validEmbedPattern(pattern string) bool {
 // as existing for embedding.
 func isBadEmbedName(name string) bool {
 	switch name {
+	// Empty string should be impossible but make it bad.
+	case "":
+		return true
 	// Version control directories won't be present in module.
 	case ".bzr", ".hg", ".git", ".svn":
 		return true

src/embed/embed.go

@@ -59,12 +59,15 @@
 // as Go double-quoted or back-quoted string literals.
 //
 // If a pattern names a directory, all files in the subtree rooted at that directory are
-// embedded (recursively), so the variable in the above example is equivalent to:
+// embedded (recursively), except that files with names beginning with ‘.’ or ‘_’
+// are excluded. So the variable in the above example is almost equivalent to:
 //
 //	// content is our static web server content.
 //	//go:embed image template html/index.html
 //	var content embed.FS
 //
+// The difference is that ‘image/*’ embeds ‘image/.tempfile’ while ‘image’ does not.
+//
 // The //go:embed directive can be used with both exported and unexported variables,
 // depending on whether the package wants to make the data available to other packages.
 // Similarly, it can be used with both global and function-local variables,

src/embed/internal/embedtest/embed_test.go

@@ -101,3 +101,24 @@ func TestDir(t *testing.T) {
 	testDir(t, all, "testdata/i/j", "k/")
 	testDir(t, all, "testdata/i/j/k", "k8s.txt")
 }
+
+func TestHidden(t *testing.T) {
+	//go:embed testdata
+	var dir embed.FS
+
+	//go:embed testdata/*
+	var star embed.FS
+
+	t.Logf("//go:embed testdata")
+
+	testDir(t, dir, "testdata",
+		"ascii.txt", "glass.txt", "hello.txt", "i/", "ken.txt")
+
+	t.Logf("//go:embed testdata/*")
+
+	testDir(t, star, "testdata",
+		".hidden/", "_hidden/", "ascii.txt", "glass.txt", "hello.txt", "i/", "ken.txt")
+
+	testDir(t, star, "testdata/.hidden",
+		"fortune.txt", "more/") // but not .more or _more
+}

src/embed/internal/embedtest/testdata/.hidden/.more/tip.txt

@@ -0,0 +1 @@
+#define struct union /* Great space saver */

src/embed/internal/embedtest/testdata/.hidden/_more/tip.txt

@@ -0,0 +1 @@
+#define struct union /* Great space saver */

src/embed/internal/embedtest/testdata/.hidden/fortune.txt

@@ -0,0 +1,2 @@
+WARNING: terminal is not fully functional
+ -  (press RETURN)

src/embed/internal/embedtest/testdata/.hidden/more/tip.txt

@@ -0,0 +1 @@
+#define struct union /* Great space saver */

src/embed/internal/embedtest/testdata/_hidden/fortune.txt

@@ -0,0 +1,2 @@
+WARNING: terminal is not fully functional
+ -  (press RETURN)