Ignore implementation files when .flow.js file exists during type t…

…ranslation (#49039)

Summary:
Pull Request resolved: #49039

Changelog: [Internal]

Reviewed By: huntie

Differential Revision: D68774523

fbshipit-source-id: 07776e7e0d551e3bad5a30eff1de8a76769e5761

scripts/build/build-types.js

@@ -56,10 +56,12 @@ async function main() {
     return;
   }
 
-  const files = SOURCE_PATTERNS.flatMap(srcPath =>
-    glob.sync(path.join(srcPath, ''), {
-      nodir: true,
-    }),
+  const files = ignoreShadowedFiles(
+    SOURCE_PATTERNS.flatMap(srcPath =>
+      glob.sync(path.join(srcPath, ''), {
+        nodir: true,
+      }),
+    ),
   );
 
   console.log(
@@ -117,6 +119,28 @@ function getBuildPath(file /*: string */) /*: string */ {
   );
 }
 
+function ignoreShadowedFiles(files /*: Array<string> */) /*: Array<string> */ {
+  const shadowedPrefixes /*: Record<string, boolean> */ = {};
+  const result /*: Array<string> */ = [];
+
+  // Find all flow definition files that shadow other files
+  for (const file of files) {
+    if (/\.flow\.js$/.test(file)) {
+      shadowedPrefixes[file.substring(0, file.length - 8)] = true;
+    }
+  }
+
+  // Filter out all files shadowed by flow definition files
+  for (const file of files) {
+    const prefix = file.split('.')[0];
+    if (/\.flow\.js$/.test(file) || !shadowedPrefixes[prefix]) {
+      result.push(file);
+    }
+  }
+
+  return result;
+}
+
 if (require.main === module) {
   // eslint-disable-next-line no-void
   void main();