Add source transformation pipeline to build-types

scripts/build/build-types.js

@@ -10,8 +10,8 @@
  */
 
 const {PACKAGES_DIR, REPO_ROOT} = require('../consts');
+const translateSourceFile = require('./build-types/translateSourceFile');
 const chalk = require('chalk');
-const translate = require('flow-api-translator');
 const {promises: fs} = require('fs');
 const glob = require('glob');
 const micromatch = require('micromatch');
@@ -62,38 +62,35 @@ async function main() {
       '\n',
   );
 
-  for (const file of files) {
-    if (micromatch.isMatch(file, IGNORE_PATTERN)) {
-      continue;
-    }
-
-    const buildPath = getBuildPath(file);
-    const source = await fs.readFile(file, 'utf-8');
-    const prettierConfig = {parser: 'babel'};
-
-    await fs.mkdir(path.dirname(buildPath), {recursive: true});
-
-    try {
-      const typescriptDef = await translate.translateFlowToTSDef(
-        source,
-        prettierConfig,
-      );
-
-      if (
-        /Unsupported feature: Translating ".*" is currently not supported/.test(
-          typescriptDef,
-        )
-      ) {
-        throw new Error(
-          'Syntax unsupported by flow-api-translator used in ' + file,
-        );
+  await Promise.all(
+    files.map(async file => {
+      if (micromatch.isMatch(file, IGNORE_PATTERN)) {
+        return;
       }
 
-      await fs.writeFile(buildPath, typescriptDef);
-    } catch (e) {
-      console.error(`Failed to build ${path.relative(REPO_ROOT, file)}`);
-    }
-  }
+      const buildPath = getBuildPath(file);
+      const source = await fs.readFile(file, 'utf-8');
+      await fs.mkdir(path.dirname(buildPath), {recursive: true});
+
+      try {
+        const typescriptDef = await translateSourceFile(source);
+
+        if (
+          /Unsupported feature: Translating ".*" is currently not supported/.test(
+            typescriptDef,
+          )
+        ) {
+          throw new Error(
+            'Syntax unsupported by flow-api-translator used in ' + file,
+          );
+        }
+
+        await fs.writeFile(buildPath, typescriptDef);
+      } catch (e) {
+        console.error(`Failed to build ${path.relative(REPO_ROOT, file)}`);
+      }
+    }),
+  );
 }
 
 function getPackageName(file /*: string */) /*: string */ {

scripts/build/build-types/transforms/stripPrivateProperties.js

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+/*::
+import type {TransformVisitor} from 'hermes-transform';
+import type {TransformASTResult} from 'hermes-transform/dist/transform/transformAST';
+import type {ParseResult} from 'hermes-transform/dist/transform/parse';
+ */
+
+const {transformAST} = require('hermes-transform/dist/transform/transformAST');
+
+const visitors /*: TransformVisitor */ = context => ({
+  // TODO
+});
+
+async function stripPrivateProperties(
+  source /*: ParseResult */,
+) /*: Promise<TransformASTResult> */ {
+  return transformAST(source, visitors);
+}
+
+module.exports = stripPrivateProperties;

scripts/build/build-types/translateSourceFile.js

@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ * @oncall react_native
+ */
+
+/*::
+import type {ParseResult} from 'hermes-transform/dist/transform/parse';
+import type {TransformASTResult} from 'hermes-transform/dist/transform/transformAST';
+*/
+
+const translate = require('flow-api-translator');
+const {parse} = require('hermes-transform');
+
+/*::
+type TransformFn = (ParseResult) => Promise<TransformASTResult>;
+*/
+
+const preTransforms /*: Array<TransformFn> */ = [
+  require('./transforms/stripPrivateProperties'),
+];
+const prettierOptions = {parser: 'babel'};
+
+/**
+ * Translate the public API of a Flow source file to TypeScript definition.
+ *
+ * This uses [flow-api-translator](https://www.npmjs.com/package/flow-api-translator),
+ * and applies extra transformations such as stripping private properties.
+ */
+async function translateSourceFile(
+  source /*: string */,
+) /*: Promise<string> */ {
+  // Parse Flow source
+  const parsed = await parse(source);
+
+  // Apply pre-transforms
+  const preTransformResult = await applyTransforms(parsed, preTransforms);
+
+  // Translate to TypeScript defs
+  return await translate.translateFlowToTSDef(
+    preTransformResult.code,
+    prettierOptions,
+  );
+}
+
+async function applyTransforms(
+  source /*: ParseResult */,
+  transforms /*: $ReadOnlyArray<TransformFn> */,
+) /*: Promise<ParseResult> */ {
+  return transforms.reduce((input, transform) => {
+    return input.then(async result => {
+      const transformed = await transform(result);
+      return {
+        ...result,
+        ast: transformed.ast,
+        code: transformed.mutatedCode,
+      };
+    });
+  }, Promise.resolve(source));
+}
+
+module.exports = translateSourceFile;