CR change

frontend/dockerfile/dockerfile_mount_test.go

@@ -24,6 +24,7 @@ var mountTests = []integration.Test{
 	testMountArg,
 	testMountEnvAcrossStages,
 	testMountMetaArg,
+	testMountFromError,
 }
 
 func init() {
@@ -348,3 +349,35 @@ RUN --mount=type=cache,id=mycache,target=$META_PATH [ -f /tmp/meta/foo ]
 	}, nil)
 	require.NoError(t, err)
 }
+
+func testMountFromError(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox as test
+RUN touch /tmp/test
+
+FROM busybox
+ENV ttt=test
+RUN --mount=from=$ttt,type=cache,target=/tmp ls
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "'from' doesn't support variable expansion")
+}

frontend/dockerfile/instructions/commands_runmount.go

@@ -125,10 +125,6 @@ func parseMount(value string, expander SingleWordExpander) (*Mount, error) {
 
 	m := &Mount{Type: MountTypeBind}
 
-	hasVariableRegex, err := regexp.Compile(`\$.`)
-	if err != nil {
-		return nil, err
-	}
 	roAuto := true
 
 	for _, field := range fields {
@@ -161,15 +157,7 @@ func parseMount(value string, expander SingleWordExpander) (*Mount, error) {
 
 		value := parts[1]
 		// check for potential variable
-		if hasVariableRegex.MatchString(value) {
-			if key == "from" {
-				return nil, errors.Errorf("'%s' doesn't support variable expansion", key)
-			}
-
-			if expander == nil {
-				// skip variable expansion for now
-				continue
-			}
+		if expander != nil {
 			processed, err := expander(value)
 			if err != nil {
 				return nil, err
@@ -179,10 +167,18 @@ func parseMount(value string, expander SingleWordExpander) (*Mount, error) {
 		switch key {
 		case "type":
 			if !isValidMountType(strings.ToLower(value)) {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("unsupported mount type %q", value)
 			}
 			m.Type = strings.ToLower(value)
 		case "from":
+			if matched, err := regexp.MatchString(`\$.`, value); err != nil { //nolint
+				return nil, err
+			} else if matched {
+				return nil, errors.Errorf("'%s' doesn't support variable expansion", key)
+			}
 			m.From = value
 		case "source", "src":
 			m.Source = value
@@ -191,12 +187,18 @@ func parseMount(value string, expander SingleWordExpander) (*Mount, error) {
 		case "readonly", "ro":
 			m.ReadOnly, err = strconv.ParseBool(value)
 			if err != nil {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("invalid value for %s: %s", key, value)
 			}
 			roAuto = false
 		case "readwrite", "rw":
 			rw, err := strconv.ParseBool(value)
 			if err != nil {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("invalid value for %s: %s", key, value)
 			}
 			m.ReadOnly = !rw
@@ -205,34 +207,52 @@ func parseMount(value string, expander SingleWordExpander) (*Mount, error) {
 			if m.Type == "secret" || m.Type == "ssh" {
 				v, err := strconv.ParseBool(value)
 				if err != nil {
+					if expander == nil {
+						continue
+					}
 					return nil, errors.Errorf("invalid value for %s: %s", key, value)
 				}
 				m.Required = v
 			} else {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("unexpected key '%s' for mount type '%s'", key, m.Type)
 			}
 		case "id":
 			m.CacheID = value
 		case "sharing":
 			if _, ok := allowedSharingTypes[strings.ToLower(value)]; !ok {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("unsupported sharing value %q", value)
 			}
 			m.CacheSharing = strings.ToLower(value)
 		case "mode":
 			mode, err := strconv.ParseUint(value, 8, 32)
 			if err != nil {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("invalid value %s for mode", value)
 			}
 			m.Mode = &mode
 		case "uid":
 			uid, err := strconv.ParseUint(value, 10, 32)
 			if err != nil {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("invalid value %s for uid", value)
 			}
 			m.UID = &uid
 		case "gid":
 			gid, err := strconv.ParseUint(value, 10, 32)
 			if err != nil {
+				if expander == nil {
+					continue
+				}
 				return nil, errors.Errorf("invalid value %s for gid", value)
 			}
 			m.GID = &gid