Remove symlink, not target, in FileOp.Rm.

Before this change, if the path provided to FileOp.Rm was a symlink then
the target of the symlink would be removed instead of the symlink
itself. Now, the symlink will be removed instead. However, any symlinks
present in the parent dirs of the specified path will still be resolved
before calling os.Remove; this change only results in the base of the
specified path not being followed.

Signed-off-by: Erik Sipsma <erik@sipsma.dev>

client/client_test.go

@@ -139,6 +139,7 @@ func TestIntegration(t *testing.T) {
 		testPullZstdImage,
 		testMergeOp,
 		testMergeOpCache,
+		testRmSymlink,
 	}, mirrors)
 
 	integration.Run(t, []integration.Test{
@@ -3824,6 +3825,41 @@ func testSourceMapFromRef(t *testing.T, sb integration.Sandbox) {
 	require.Equal(t, int32(1), srcs[0].Ranges[0].Start.Character)
 }
 
+func testRmSymlink(t *testing.T, sb integration.Sandbox) {
+	c, err := New(sb.Context(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	// Test that if FileOp.Rm is called on a symlink, then
+	// the symlink is removed rather than the target
+	mnt := llb.Image("alpine").
+		Run(llb.Shlex("touch /mnt/target")).
+		AddMount("/mnt", llb.Scratch())
+
+	mnt = llb.Image("alpine").
+		Run(llb.Shlex("ln -s target /mnt/link")).
+		AddMount("/mnt", mnt)
+
+	def, err := mnt.File(llb.Rm("link")).Marshal(sb.Context())
+	require.NoError(t, err)
+
+	destDir, err := ioutil.TempDir("", "buildkit")
+	require.NoError(t, err)
+	defer os.RemoveAll(destDir)
+
+	_, err = c.Solve(sb.Context(), def, SolveOpt{
+		Exports: []ExportEntry{
+			{
+				Type:      ExporterLocal,
+				OutputDir: destDir,
+			},
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	require.NoError(t, fstest.CheckDirectoryEqualWithApplier(destDir, fstest.CreateFile("target", nil, 0644)))
+}
+
 func testProxyEnv(t *testing.T, sb integration.Sandbox) {
 	c, err := New(sb.Context(), sb.Address())
 	require.NoError(t, err)

solver/llbsolver/file/backend.go

@@ -146,10 +146,16 @@ func rm(ctx context.Context, d string, action pb.FileActionRm) error {
 }
 
 func rmPath(root, src string, allowNotFound bool) error {
-	p, err := fs.RootPath(root, filepath.Join("/", src))
+	src = filepath.Clean(src)
+	dir, base := filepath.Split(src)
+	if base == "" {
+		return errors.New("rmPath: invalid empty path")
+	}
+	dir, err := fs.RootPath(root, filepath.Join("/", dir))
 	if err != nil {
 		return err
 	}
+	p := filepath.Join(dir, base)
 
 	if err := os.RemoveAll(p); err != nil {
 		if errors.Is(err, os.ErrNotExist) && allowNotFound {

solver/pb/caps.go

@@ -57,6 +57,7 @@ const (
 	CapFileBase                       apicaps.CapID = "file.base"
 	CapFileRmWildcard                 apicaps.CapID = "file.rm.wildcard"
 	CapFileCopyIncludeExcludePatterns apicaps.CapID = "file.copy.includeexcludepatterns"
+	CapFileRmNoFollowSymlink          apicaps.CapID = "file.rm.nofollowsymlink"
 
 	CapConstraints apicaps.CapID = "constraints"
 	CapPlatform    apicaps.CapID = "platform"
@@ -328,6 +329,12 @@ func init() {
 		Status:  apicaps.CapStatusExperimental,
 	})
 
+	Caps.Init(apicaps.Cap{
+		ID:      CapFileRmNoFollowSymlink,
+		Enabled: true,
+		Status:  apicaps.CapStatusExperimental,
+	})
+
 	Caps.Init(apicaps.Cap{
 		ID:      CapFileCopyIncludeExcludePatterns,
 		Enabled: true,