Add flow to devDeps & fix minor type errors

Author: STRML

.flowconfig

@@ -0,0 +1,2 @@
+[options]
+sharedmemory.heap_size=3221225472

babel-watch.js

@@ -1,4 +1,5 @@
 #!/usr/bin/env node
+// @flow
 
 'use strict';
 
@@ -34,7 +35,7 @@ function collect(val, memo) {
 // Plucked directly from old Babel Core
 // https://github.com/babel/babel/commit/0df0c696a93889f029982bf36d34346a039b1920
 function regexify(val) {
-  if (!val) return new RegExp;
+  if (!val) return new RegExp('');
   if (Array.isArray(val)) val = val.join("|");
   if (isString(val)) return new RegExp(val || "");
   if (isRegExp(val)) return val;
@@ -204,7 +205,7 @@ function handleChange(file) {
 function generateTempFilename() {
   const now = new Date();
   return path.join(os.tmpdir(), [
-    now.getYear(), now.getMonth(), now.getDate(),
+    now.getFullYear(), now.getMonth(), now.getDate(),
     '-',
     process.pid,
     '-',
@@ -224,7 +225,9 @@ function handleFileLoad(filename, callback) {
   if (!shouldIgnore(filename)) {
     compile(filename, (err, result) => {
       debugCompile('Compiled file: %s. Success? %s', filename, !err);
-      if (err) {
+
+      if (!result && !err) err = new Error('No Result from Babel for file: ' + filename);
+      if (err || !result) {
         // Intentional ignore
         if (err instanceof IgnoredFileError) {
           ignored[filename] = true;
@@ -395,9 +398,9 @@ function restartAppInternal() {
       watcher.add(relativeFilename);
     }
     handleFileLoad(filename, (source, sourceMap) => {
-      const sourceBuf = new Buffer.from(source || '');
-      const mapBuf = new Buffer.from(sourceMap ? JSON.stringify(sourceMap) : []);
-      const lenBuf = new Buffer.alloc(4);
+      const sourceBuf = Buffer.from(source || '');
+      const mapBuf = Buffer.from(sourceMap ? JSON.stringify(sourceMap) : []);
+      const lenBuf = Buffer.alloc(4);
       if (pipeFd) {
         try {
           lenBuf.writeUInt32BE(sourceBuf.length, 0);

package.json

@@ -51,6 +51,7 @@
     "babel-watch": "./babel-watch.js"
   },
   "devDependencies": {
-    "@babel/core": "^7.12.10"
+    "@babel/core": "^7.12.10",
+    "flow-bin": "^0.141.0"
   }
 }

runner.js

@@ -1,4 +1,4 @@
-'use strict';
+// @flow
 
 const path = require('path');
 const fs = require('fs');
@@ -10,21 +10,26 @@ let maps = {};
 let pipeFd;
 const BUFFER = new Buffer.alloc(10 * 1024);
 
+// $FlowIgnore Flow doesn't recognize require.extensions
+const reqExtensions/*: any */ = require.extensions;
+
 // Node by default uses '.js' loader to load all the files with unknown extensions
-const DEFAULT_LOADER = require.extensions['.js'];
+const DEFAULT_LOADER = reqExtensions['.js'];
 
 function readLength(fd) {
   let bytes = 0;
   while (typeof bytes === 'number' && bytes !== 4) {
-    bytes = fs.readSync(fd, BUFFER, 0, 4);
+    // $FlowIgnore position can be null
+    bytes = fs.readSync(fd, BUFFER, 0, 4, null);
   }
   return BUFFER.readUInt32BE(0);
 }
 
 function readFileFromPipeSync(fd) {
   let length = readLength(fd);
-  let result = new Buffer.alloc(0);
+  let result = Buffer.alloc(0);
   while (length > 0) {
+    // $FlowIgnore position can be null
     const newBytes = fs.readSync(fd, BUFFER, 0, Math.min(BUFFER.length, length));
     length -= newBytes;
     result = Buffer.concat([result, BUFFER], result.length + newBytes);
@@ -40,6 +45,8 @@ function babelWatchLoader(module_, filename, defaultHandler) {
   // a named unix pipe (mkfifo). All the alternative ways would
   // require writing native code which usually brings large
   // dependencies to the project and I prefer to avoid that
+  //
+  // $FlowIgnore we know process.send exists b/c this is a child process
   process.send({
     event: 'babel-watch-filename',
     filename: filename,
@@ -55,8 +62,8 @@ function babelWatchLoader(module_, filename, defaultHandler) {
 }
 
 function registerExtension(ext) {
-  const defaultHandler = require.extensions[ext] || DEFAULT_LOADER;
-  require.extensions[ext] = (module_, filename) => {
+  const defaultHandler = reqExtensions[ext] || DEFAULT_LOADER;
+  reqExtensions[ext] = (module_, filename) => {
     // ignore node_modules by default. don't you dare contacting the parent process!
     if (filename.split(path.sep).indexOf('node_modules') < 0) {
       babelWatchLoader(module_, filename, defaultHandler);
@@ -74,12 +81,12 @@ function registerExtension(ext) {
 }
 
 function replaceExtensionHooks(extensions) {
-  for (const ext in require.extensions) {
+  for (const ext in reqExtensions) {
     registerExtension(ext);
   }
   for (let i = 0; i < extensions.length; i++) {
     const ext = extensions[i];
-    if (!(ext in require.extensions)) {
+    if (!(ext in reqExtensions)) {
       registerExtension(ext);
     }
   }
@@ -108,5 +115,6 @@ process.on('message', (options) => {
 
   pipeFd = fs.openSync(options.pipe, 'r');
   process.argv = ["node"].concat(options.args);
+  // $FlowIgnore doesn't recognize 'module' as it is internal
   require('module').runMain();
 });

yarn.lock

@@ -302,6 +302,11 @@ fill-range@^7.0.1:
   dependencies:
     to-regex-range "^5.0.1"
 
+flow-bin@^0.141.0:
+  version "0.141.0"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.141.0.tgz#f9e33ad29392824823c97b6db7de5ab972c7f872"
+  integrity sha512-NxaECTjIWfs2Y91GuA1PlgPd5uCulZcqR9wiXRg6n7/AbmvVetM2ewoGxCKxJm7wIml3f0/5KXIZvZa/3msqXg==
+
 fsevents@~2.1.2:
   version "2.1.2"
   resolved "https://registry.yarnpkg.com/fsevents/-/fsevents-2.1.2.tgz#4c0a1fb34bc68e543b4b82a9ec392bfbda840805"