expand: fix globbing with symlinks

This was causing a test to fail on Mac, since the temporary dir used
there was under /var, which is a symlink to a directory.

This does require an extra syscall in that edge case. We might get rid
of that at some point. For now, fix the bug.

expand/expand.go

@@ -685,10 +685,20 @@ func (cfg *Config) globDir(base, dir string, rx *regexp.Regexp, wantDir bool, ma
 		return nil, err
 	}
 	for _, info := range infos {
-		if wantDir && !info.IsDir() {
+		name := info.Name()
+		if !wantDir {
+			// no filtering
+		} else if mode := info.Mode(); mode&os.ModeSymlink != 0 {
+			// TODO: is there a way to do this without the
+			// extra syscall?
+			if _, err := cfg.ReadDir(filepath.Join(fullDir, name)); err != nil {
+				// symlink pointing to non-directory
+				continue
+			}
+		} else if !mode.IsDir() {
+			// definitely not a directory
 			continue
 		}
-		name := info.Name()
 		if !strings.HasPrefix(rx.String(), `^\.`) && name[0] == '.' {
 			continue
 		}

interp/interp_test.go

@@ -2098,6 +2098,14 @@ set +o pipefail
 		"mkdir x-d; touch x-f; test -d $PWD/x-*/",
 		"",
 	},
+	{
+		"mkdir -p foo/bar; ln -s foo sym; echo sy*/; echo sym/b*",
+		"sym/\nsym/bar\n",
+	},
+	{
+		"touch foo; ln -s foo sym; echo sy*; echo sy*/",
+		"sym\nsy*/\n",
+	},
 
 	// brace expansion; more exhaustive tests in the syntax package
 	{"echo a}b", "a}b\n"},