add transform for toggling isEsm flag

tools/package.json

@@ -34,7 +34,6 @@
     "rimraf": "^5.0.1",
     "@babel/core": "^7.22.5",
     "@babel/traverse": "^7.22.5",
-    "@types/rimraf": "^3.0.2",
     "uglify-js": "^3.17.0",
     "walkdir": "^0.4.0"
   },

tools/src/toggleESMFlagVariable.ts

@@ -0,0 +1,44 @@
+// Copyright 2023 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.
+
+import {Visitor, types} from '@babel/core';
+
+export interface PluginOptions {
+  opts?: {
+    variableIdentifier?: string;
+    replacementValue?: boolean;
+  };
+}
+
+export default function toggleESMFlagVariable(): {
+  visitor: Visitor<PluginOptions>;
+} {
+  return {
+    visitor: {
+      VariableDeclarator(path, state) {
+        const opts = state.opts || {};
+        const variableIdentifier = opts.variableIdentifier || 'isEsm';
+        const replacementValue = opts.replacementValue || false;
+        const {node} = path;
+        const identifier = node.id as types.Identifier;
+        if (
+          identifier.name === variableIdentifier &&
+          node.init?.type === 'BooleanLiteral'
+        ) {
+          node.init.value = replacementValue;
+        }
+      },
+    },
+  };
+}

tools/test/toggleESMFlagVariable.ts

@@ -0,0 +1,73 @@
+// Copyright 2023 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.
+
+import {describe, it} from 'mocha';
+import * as babel from '@babel/core';
+import toggleESMFlagVariable from '../src/toggleESMFlagVariable';
+import * as assert from 'assert';
+
+describe('toggle ESM flag variable', () => {
+  it('does not replace a non-boolean variable named isEsm', async () => {
+    const program = 'const isEsm = 100;';
+    const result = await babel.transformAsync(program, {
+      plugins: [toggleESMFlagVariable],
+    });
+
+    assert.strictEqual(result?.code, program);
+  });
+
+  it('replaces isEsm with the default value of false when no argument provided', async () => {
+    const program = 'const isEsm = true;';
+    const expected = 'const isEsm = false;';
+    const result = await babel.transformAsync(program, {
+      plugins: [toggleESMFlagVariable],
+    });
+
+    assert.strictEqual(result?.code, expected);
+  });
+
+  it('does not replace the user defined variable name when it is non-boolean', async () => {
+    const program = 'const foo = 100;';
+    const result = await babel.transformAsync(program, {
+      plugins: [[toggleESMFlagVariable, {variableIdentifier: 'foo'}]],
+    });
+
+    assert.strictEqual(result?.code, program);
+  });
+
+  it('replaces the user defined variable name with the default value of false', async () => {
+    const program = 'const foo = true;';
+    const expected = 'const foo = false;';
+    const result = await babel.transformAsync(program, {
+      plugins: [[toggleESMFlagVariable, {variableIdentifier: 'foo'}]],
+    });
+
+    assert.strictEqual(result?.code, expected);
+  });
+
+  it('replaces the user defined variable name with the user defined value', async () => {
+    const program = 'const foo = false;';
+    const expected = 'const foo = true;';
+    const result = await babel.transformAsync(program, {
+      plugins: [
+        [
+          toggleESMFlagVariable,
+          {variableIdentifier: 'foo', replacementValue: true},
+        ],
+      ],
+    });
+
+    assert.strictEqual(result?.code, expected);
+  });
+});

tools/tsconfig.json

@@ -7,5 +7,12 @@
     "noImplicitAny": true,
     "resolveJsonModule": true,
   },
-  "include": ["src/*.ts","test/minify.ts", "test/compileProtos.ts", "test/replaceImportMetaUrl.ts", "test/replaceESMMockingLib.ts"]
+  "include": [
+    "src/*.ts",
+    "test/minify.ts",
+    "test/compileProtos.ts",
+    "test/replaceImportMetaUrl.ts",
+    "test/replaceESMMockingLib.ts",
+    "test/toggleESMFlagVariable.ts"
+  ]
 }