Migration: add assemble_resources.dart script.

This script does the same job as `generate_resources.dart`, but it
doesn't search the filesystem for the input files to use, nor invoke
the compiler to create the `migration.js` file.  Instead, it simply
accepts a list of input files on the command line, and outputs their
contents in an appropriate form to be stored in `resources.g.dart`.

This script will allow us to integrate more cleanly with the internal
build system.

Change-Id: I4b5445d1f5fd7eccbb5fb36f6ee4fa97d2cea87e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/254421
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/nnbd_migration/tool/codegen/assemble_resources.dart

@@ -0,0 +1,34 @@
+// Copyright (c) 2022, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This script provides an alternative way of creating the
+// lib/src/front_end/resources/resources.g.dart file, based on a set of provided
+// files that has already been suitably compiled.
+
+import 'dart:io';
+
+import 'package:args/args.dart';
+
+import 'generate_resources.dart';
+
+main(List<String> args) {
+  var argParser = ArgParser()
+    ..addOption('output', abbr: 'o', help: 'Output to FILE', valueHelp: 'FILE')
+    ..addFlag('help', abbr: 'h', negatable: false, help: 'Show help');
+  var parsedArgs = argParser.parse(args);
+  if (parsedArgs['help'] as bool) {
+    print('Usage: dart assemble_resources.dart INPUT_FILES');
+    print('');
+    print(argParser.usage);
+    exit(1);
+  }
+  var content =
+      generateResourceFile([for (var arg in parsedArgs.rest) File(arg)]);
+  var output = parsedArgs['output'] as String?;
+  if (output == null) {
+    stdout.write(content);
+  } else {
+    File(output).writeAsStringSync(content);
+  }
+}

pkg/nnbd_migration/tool/codegen/generate_resources.dart

@@ -110,11 +110,12 @@ Future<void> compileWebFrontEnd(
 }
 
 void createResourcesGDart() {
-  var content =
-      generateResourceFile(sortDir(resourceDir.listSync()).where((entity) {
-    var name = path.basename(entity.path);
-    return entity is File && resourceTypes.contains(path.extension(name));
-  }).cast<File>());
+  var content = generateResourceFile(
+      sortDir(resourceDir.listSync()).where((entity) {
+        var name = path.basename(entity.path);
+        return entity is File && resourceTypes.contains(path.extension(name));
+      }).cast<File>(),
+      sourcesMd5: _computeSourcesMd5());
 
   // write the content
   resourcesFile.writeAsStringSync(content);
@@ -149,7 +150,7 @@ To re-generate lib/src/front_end/resources/resources.g.dart, run:
   exit(1);
 }
 
-String generateResourceFile(Iterable<File> resources) {
+String generateResourceFile(Iterable<File> resources, {String? sourcesMd5}) {
   var filePath = path.relative(Platform.script.toFilePath());
   var buf = StringBuffer('''
 // Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
@@ -196,17 +197,10 @@ String _decode(String data) {
 
     buf.writeln();
     buf.writeln('String? _$name;');
-    if (name == path.basename(javascriptOutput.path).replaceAll('.', '_')) {
+    if (sourcesMd5 != null &&
+        name == path.basename(javascriptOutput.path).replaceAll('.', '_')) {
       // Write out the crc for the dart code.
-      var sourceCode = StringBuffer();
-      // collect the dart source code
-      for (var entity in sortDir(dartSources.parent.listSync())) {
-        if (entity.path.endsWith('.dart')) {
-          sourceCode.write((entity as File).readAsStringSync());
-        }
-      }
-      buf.writeln(
-          "// migration_dart md5 is '${md5String(sourceCode.toString())}'");
+      buf.writeln("// migration_dart md5 is '$sourcesMd5'");
     } else {
       // highlight_css md5 is 'fb012626bafd286510d32da815dae448'
       buf.writeln("// $name md5 is '${md5String(source)}'");
@@ -272,18 +266,24 @@ void verifyResourcesGDartGenerated({
   }
 
   // verify the compiled dart code
+  String hash = _computeSourcesMd5();
+  if (hash != resourceHashes['migration_dart']) {
+    failVerification('Compiled javascript not up to date in resources.g.dart');
+  }
+
+  print('Generated resources up to date.');
+}
+
+String _computeSourcesMd5() {
   var sourceCode = StringBuffer();
+  // collect the dart source code
   for (var entity in sortDir(dartSources.parent.listSync())) {
     if (entity.path.endsWith('.dart')) {
       sourceCode.write((entity as File).readAsStringSync());
     }
   }
-  var hash = md5String(sourceCode.toString());
-  if (hash != resourceHashes['migration_dart']) {
-    failVerification('Compiled javascript not up to date in resources.g.dart');
-  }
-
-  print('Generated resources up to date.');
+  var sourcesMd5 = md5String(sourceCode.toString());
+  return sourcesMd5;
 }
 
 typedef VerificationFunction = void Function(String);