feat: add downconversion from ?? to || (#3722)

* feat: add downconversion from ?? to ||

* chore: fix linter issues

Author: feywind

packages/typeless-sample-bot/__snapshots__/index.js

@@ -22,6 +22,7 @@ import babel from '@babel/core';
 import path from 'node:path';
 import {typescript as presetTypescript} from './preset-loader.js';
 import importToRequire from './transforms/import-to-require.js';
+import nullCoalescing from './transforms/null-coalescing.js';
 import {addComments} from './transforms/add-comments.js';
 
 // Converts an async iterable into an array of the same type.
@@ -84,7 +85,7 @@ export async function* filterByContents(
 // the transform process.
 const babelConfig = {
   presets: [[presetTypescript, {}]],
-  plugins: [[importToRequire]],
+  plugins: [[importToRequire], [nullCoalescing]],
   parserOpts: {} as babel.ParserOptions,
   generatorOpts: {
     // Ensures that Babel keeps newlines so that comments end up

packages/typeless-sample-bot/src/samples.ts

@@ -0,0 +1,28 @@
+// Copyright 2022 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.
+
+// Reference notes:
+// https://lihautan.com/step-by-step-guide-for-writing-a-babel-transformation/
+// https://lihautan.com/babel-ast-explorer/
+// https://github.com/esamattis/babel-plugin-ts-optchain/blob/master/packages/babel-plugin-ts-optchain/src/plugin.ts
+
+import {NodePath, Visitor} from '@babel/traverse';
+import * as Babel from '@babel/types';
+
+export interface VisitorPlugin {
+  visitor: Visitor<unknown>;
+}
+
+export type NodePathArray = NodePath<Babel.Node>[];
+export type NodePathSingle = NodePath<Babel.Node>;

packages/typeless-sample-bot/src/transforms/babel.ts

@@ -12,16 +12,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Reference notes:
-// https://lihautan.com/step-by-step-guide-for-writing-a-babel-transformation/
-// https://lihautan.com/babel-ast-explorer/
-// https://github.com/esamattis/babel-plugin-ts-optchain/blob/master/packages/babel-plugin-ts-optchain/src/plugin.ts
-
 import * as Babel from '@babel/types';
-import {NodePath, Visitor} from '@babel/traverse';
-
-type NodePathArray = NodePath<Babel.Node>[];
-type NodePathSingle = NodePath<Babel.Node>;
+import {NodePath} from '@babel/traverse';
+import {NodePathArray, NodePathSingle, VisitorPlugin} from './babel';
 
 function getArray(path: NodePathSingle, subPathName: string): NodePathArray {
   return path.get(subPathName) as NodePathArray;
@@ -102,10 +95,6 @@ function wildcardImport(path: NodePathSingle) {
   path.replaceWith(replacement);
 }
 
-interface VisitorPlugin {
-  visitor: Visitor<unknown>;
-}
-
 export default function importToRequire(): VisitorPlugin {
   return {
     visitor: {

packages/typeless-sample-bot/src/transforms/import-to-require.ts

@@ -0,0 +1,33 @@
+// Copyright 2022 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 * as Babel from '@babel/types';
+import {NodePathSingle, VisitorPlugin} from './babel';
+
+// Because null coalescing is still a proposal in many versions of Node,
+// go ahead and convert it to plain ||. It should work in TypeScript.
+export default function nullCoalescing(): VisitorPlugin {
+  return {
+    visitor: {
+      LogicalExpression(path: NodePathSingle) {
+        const node = path.node as Babel.LogicalExpression;
+        if (node.operator === '??') {
+          path.replaceWith(
+            Babel.logicalExpression('||', node.left, node.right)
+          );
+        }
+      },
+    },
+  };
+}

packages/typeless-sample-bot/src/transforms/null-coalescing.ts

@@ -45,6 +45,9 @@ async function deleteSchema(schemaNameOrId: string) {
 }
 // [END pubsub_delete_schema]
 
+const someValue: number | undefined = undefined;
+const coalesced = someValue ?? 5;
+
 function main(schemaNameOrId = 'YOUR_SCHEMA_NAME_OR_ID') {
   deleteSchema(schemaNameOrId).catch(err => {
     console.error(err.message);