archive/tar: append a slash when deriving header info from a directory

This behavior is identical to GNU tar 1.26.

R=dsymonds, dave
CC=golang-dev
https://golang.org/cl/7307101

src/pkg/archive/tar/common.go

@@ -79,6 +79,7 @@ const (
 
 // FileInfoHeader creates a partially-populated Header from fi.
 // If fi describes a symlink, FileInfoHeader records link as the link target.
+// If fi describes a directory, a slash is appended to the name.
 func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
 	if fi == nil {
 		return nil, errors.New("tar: FileInfo is nil")
@@ -96,6 +97,7 @@ func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
 	case fi.IsDir():
 		h.Typeflag = TypeDir
 		h.Mode |= c_ISDIR
+		h.Name += "/"
 	case fi.Mode()&os.ModeSymlink != 0:
 		h.Typeflag = TypeSymlink
 		h.Mode |= c_ISLNK

src/pkg/archive/tar/tar_test.go

@@ -14,13 +14,13 @@ import (
 )
 
 func TestFileInfoHeader(t *testing.T) {
-	fi, err := os.Lstat("testdata/small.txt")
+	fi, err := os.Stat("testdata/small.txt")
 	if err != nil {
 		t.Fatal(err)
 	}
 	h, err := FileInfoHeader(fi, "")
 	if err != nil {
-		t.Fatalf("on small.txt: %v", err)
+		t.Fatalf("FileInfoHeader: %v", err)
 	}
 	if g, e := h.Name, "small.txt"; g != e {
 		t.Errorf("Name = %q; want %q", g, e)
@@ -36,6 +36,29 @@ func TestFileInfoHeader(t *testing.T) {
 	}
 }
 
+func TestFileInfoHeaderDir(t *testing.T) {
+	fi, err := os.Stat("testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h, err := FileInfoHeader(fi, "")
+	if err != nil {
+		t.Fatalf("FileInfoHeader: %v", err)
+	}
+	if g, e := h.Name, "testdata/"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Mode, int64(fi.Mode().Perm())|c_ISDIR; g != e {
+		t.Errorf("Mode = %#o; want %#o", g, e)
+	}
+	if g, e := h.Size, int64(0); g != e {
+		t.Errorf("Size = %v; want %v", g, e)
+	}
+	if g, e := h.ModTime, fi.ModTime(); !g.Equal(e) {
+		t.Errorf("ModTime = %v; want %v", g, e)
+	}
+}
+
 func TestFileInfoHeaderSymlink(t *testing.T) {
 	h, err := FileInfoHeader(symlink{}, "some-target")
 	if err != nil {