Skip syntax error checking users functions using ESM

This is a temporary workaround for a regression in Node.js 16 that causes `node --check` to return false positives when a project is using ESM.

More information here:
GoogleCloudPlatform/functions-framework-nodejs#407

PiperOrigin-RevId: 423439009
Change-Id: I26ad943e8fb55e868ece996bd5d2f7470afbec5a

builders/gcf/nodejs14/acceptance/acceptance_test.go

@@ -141,6 +141,12 @@ func TestAcceptance(t *testing.T) {
 			MustUse:    []string{npm},
 			MustNotUse: []string{yarn},
 		},
+		{
+			Name:       "ESM function",
+			App:        "using_esm",
+			MustUse:    []string{npm},
+			MustNotUse: []string{yarn},
+		},
 	}
 	for _, tc := range testCases {
 		tc := tc

builders/gcf/nodejs16/acceptance/acceptance_test.go

@@ -141,6 +141,12 @@ func TestAcceptance(t *testing.T) {
 			MustUse:    []string{npm},
 			MustNotUse: []string{yarn},
 		},
+		{
+			Name:       "ESM function",
+			App:        "using_esm",
+			MustUse:    []string{npm},
+			MustNotUse: []string{yarn},
+		},
 	}
 	for _, tc := range testCases {
 		tc := tc

builders/testdata/nodejs/functions/using_esm/function.js

@@ -0,0 +1,26 @@
+/**
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Always responds 'PASS'. The use of `export` validates the runtime's support
+ * for ESM.
+ *
+ * @param {!Object} req request context.
+ * @param {!Object} res response context.
+ */
+export const testFunction = (req, res) => {
+  res.send('PASS');
+};

builders/testdata/nodejs/functions/using_esm/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}

cmd/nodejs/functions_framework/main.go

@@ -83,8 +83,14 @@ func buildFn(ctx *gcp.Context) error {
 		return gcp.UserErrorf("%s does not exist", fnFile)
 	}
 
-	// Syntax check the function code without executing to prevent run-time errors.
-	ctx.Exec([]string{"node", "--check", fnFile}, gcp.WithUserAttribution)
+	// TODO(mattrobertson) remove this check once Nodejs has backported the fix to v16. More info here:
+	// https://github.com/GoogleCloudPlatform/functions-framework-nodejs/issues/407
+	if skip, err := nodejs.SkipSyntaxCheck(ctx, fnFile); err != nil {
+		return err
+	} else if !skip {
+		// Syntax check the function code without executing to prevent run-time errors.
+		ctx.Exec([]string{"node", "--check", fnFile}, gcp.WithUserAttribution)
+	}
 
 	l := ctx.Layer(layerName, gcp.BuildLayer, gcp.CacheLayer, gcp.LaunchLayer)
 	// We use the absolute path to the functions-framework executable in order to

pkg/nodejs/nodejs.go

@@ -21,6 +21,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/GoogleCloudPlatform/buildpacks/pkg/cache"
 	gcp "github.com/GoogleCloudPlatform/buildpacks/pkg/gcpbuildpack"
@@ -54,6 +55,7 @@ type packageScriptsJSON struct {
 // PackageJSON represents the contents of a package.json file.
 type PackageJSON struct {
 	Main            string             `json:"main"`
+	Type            string             `json:"type"`
 	Version         string             `json:"version"`
 	Engines         packageEnginesJSON `json:"engines"`
 	Scripts         packageScriptsJSON `json:"scripts"`
@@ -130,3 +132,23 @@ func CheckCache(ctx *gcp.Context, l *libcnb.Layer, opts ...cache.Option) (bool,
 
 	return false, nil
 }
+
+// SkipSyntaxCheck returns true if we should skip checking the user's function file for syntax errors
+// if it is impacted by https://github.com/GoogleCloudPlatform/functions-framework-nodejs/issues/407.
+func SkipSyntaxCheck(ctx *gcp.Context, file string) (bool, error) {
+	version, err := semver.ParseTolerant(nodeVersion(ctx))
+	if err != nil {
+		return false, gcp.InternalErrorf("failed to detect valid Node.js version %s: %v", version, err)
+	}
+	if version.Major != 16 {
+		return false, nil
+	}
+	if strings.HasSuffix(file, ".mjs") {
+		return true, nil
+	}
+	if !ctx.FileExists(filepath.Join(ctx.ApplicationRoot(), "package.json")) {
+		return false, nil
+	}
+	pjs, err := ReadPackageJSON(ctx.ApplicationRoot())
+	return (pjs != nil && pjs.Type == "module"), err
+}

pkg/nodejs/nodejs_test.go

@@ -15,9 +15,11 @@
 package nodejs
 
 import (
+	"path/filepath"
 	"reflect"
 	"testing"
 
+	gcp "github.com/GoogleCloudPlatform/buildpacks/pkg/gcpbuildpack"
 	"github.com/GoogleCloudPlatform/buildpacks/pkg/testdata"
 )
 
@@ -47,3 +49,60 @@ func TestReadPackageJSON(t *testing.T) {
 		t.Errorf("ReadPackageJSON\ngot %#v\nwant %#v", *got, want)
 	}
 }
+
+func TestSkipSyntaxCheck(t *testing.T) {
+	testCases := []struct {
+		name        string
+		version     string
+		packageJSON string
+		filePath    string
+		want        bool
+	}{
+		{
+			name:        "Node.js 14",
+			version:     "v14.1.1",
+			packageJSON: `{"type": "module"}`,
+			filePath:    "index.mjs",
+			want:        false,
+		},
+		{
+			name:     "Node.js 16 with mjs",
+			version:  "v16.1.1",
+			filePath: "index.mjs",
+			want:     true,
+		},
+		{
+			name:        "Node.js 16 with modules",
+			version:     "v16.1.1",
+			packageJSON: `{"type": "module"}`,
+			want:        true,
+		},
+		{
+			name:    "Node.js 16 without ESM",
+			version: "v16.1.1",
+			want:    false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			defer func(fn func(*gcp.Context) string) { nodeVersion = fn }(nodeVersion)
+			nodeVersion = func(*gcp.Context) string { return tc.version }
+
+			home := t.TempDir()
+			ctx := gcp.NewContext(gcp.WithApplicationRoot(home))
+
+			if tc.packageJSON != "" {
+				ctx.WriteFile(filepath.Join(home, "package.json"), []byte(tc.packageJSON), 0744)
+			}
+
+			got, err := SkipSyntaxCheck(ctx, tc.filePath)
+			if err != nil {
+				t.Fatalf("Node.js %v: SkipSyntaxCheck(ctx, %q) got error: %v", tc.version, tc.filePath, err)
+			}
+			if got != tc.want {
+				t.Errorf("Node.js %v: SkipSyntaxCheck(ctx, %q) = %t, want %t", tc.version, tc.filePath, got, tc.want)
+			}
+		})
+	}
+}