Support wasm source maps (#3759)

Fixes #3757

Author: jakemac53

.gitignore

@@ -7,8 +7,8 @@ pubspec.lock
 # Common build output
 /*/build/
 
-# Include .packages files from tests which are hand coded
-!build_runner_core/test/fixtures/**/.dart_tool/
+# Include package config files from tests which are hand coded
+!build_runner_core/test/fixtures/**/.dart_tool/package_config.json
 !build_runner_core/test/fixtures/**/pubspec.lock
 
 # Extra files from dart2js that we don't want

build_web_compilers/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 4.1.0-beta.2
+
+- Add source maps for dart2wasm builds.
+
 ## 4.1.0-beta.1
 
 - Fix loading compiled modules from subdirectories.

build_web_compilers/build.yaml

@@ -113,6 +113,7 @@ builders:
         - .digests
         - .dart.ddc_merged_metadata
         - .wasm
+        - .wasm.map
         - .mjs
     required_inputs:
       - .dart

build_web_compilers/lib/src/common.dart

@@ -2,6 +2,7 @@
 // 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.
 
+import 'dart:convert';
 import 'dart:io';
 
 import 'package:build/build.dart';
@@ -38,21 +39,34 @@ void validateOptions(Map<String, dynamic> config, List<String> supportedOptions,
   }
 }
 
-/// Fixes up the [uris] from a source map so they make sense in a browser
-/// context.
+/// If [id] exists, assume it is a source map and fix up the source uris from
+/// it so they make sense in a browser context, then write the modified version
+/// using [writer].
 ///
 /// - Strips the scheme from the uri
 /// - Strips the top level directory if its not `packages`
-///
-/// Copied to `web/stack_trace_mapper.dart`, these need to be kept in sync.
-List<String> fixSourceMapSources(List<String> uris) {
-  return uris.map((source) {
+Future<void> fixAndCopySourceMap(
+    AssetId id, ScratchSpace scratchSpace, AssetWriter writer) async {
+  // Copied to `web/stack_trace_mapper.dart`, these need to be kept in sync.
+  String fixMappedSource(String source) {
     var uri = Uri.parse(source);
     // We only want to rewrite multi-root scheme uris.
     if (uri.scheme.isEmpty) return source;
     var newSegments = uri.pathSegments.first == 'packages'
         ? uri.pathSegments
         : uri.pathSegments.skip(1);
     return Uri(path: p.url.joinAll(['/', ...newSegments])).toString();
-  }).toList();
+  }
+
+  var file = scratchSpace.fileFor(id);
+  if (await file.exists()) {
+    var content = await file.readAsString();
+    var json = jsonDecode(content) as Map<String, Object?>;
+    var sources = json['sources'] as List<Object?>;
+    // Modify `sources` in place for fewer allocations.
+    for (var i = 0; i < sources.length; i++) {
+      sources[i] = fixMappedSource(sources[i] as String);
+    }
+    await writer.writeAsString(id, jsonEncode(json));
+  }
 }

build_web_compilers/lib/src/dart2js_bootstrap.dart

@@ -14,7 +14,6 @@ import 'package:glob/glob.dart';
 import 'package:glob/list_local_fs.dart';
 import 'package:path/path.dart' as p;
 import 'package:pool/pool.dart';
-import 'package:scratch_space/scratch_space.dart';
 
 import 'common.dart';
 import 'platforms.dart';
@@ -140,28 +139,16 @@ https://github.com/dart-lang/build/blob/master/docs/faq.md#how-can-i-resolve-ski
     // Explicitly write out the original js file and sourcemap - we can't output
     // these as part of the archive because they already have asset nodes.
     await scratchSpace.copyOutput(jsOutputId, buildStep);
-    var jsSourceMapId =
-        dartEntrypointId.changeExtension(jsEntrypointSourceMapExtension);
-    await _copyModifiedSourceMap(jsSourceMapId, scratchSpace, buildStep);
+    await fixAndCopySourceMap(
+        dartEntrypointId.changeExtension(jsEntrypointSourceMapExtension),
+        scratchSpace,
+        buildStep);
   } else {
     log.severe('ExitCode:${result.exitCode}\nStdOut:\n${result.stdout}\n'
         'StdErr:\n${result.stderr}');
   }
 }
 
-/// If [id] exists, modifies it to something the browser can understand and
-/// writes it using [writer].
-Future<void> _copyModifiedSourceMap(
-    AssetId id, ScratchSpace scratchSpace, AssetWriter writer) async {
-  var file = scratchSpace.fileFor(id);
-  if (await file.exists()) {
-    var content = await file.readAsString();
-    var json = jsonDecode(content) as Map<String, Object?>;
-    json['sources'] = fixSourceMapSources((json['sources'] as List).cast());
-    await writer.writeAsString(id, jsonEncode(json));
-  }
-}
-
 final _resourcePool = Pool(maxWorkersPerTask);
 
 const _dart2jsVmArgsEnvVar = 'BUILD_DART2JS_VM_ARGS';

build_web_compilers/lib/src/dart2wasm_bootstrap.dart

@@ -107,8 +107,12 @@ https://github.com/dart-lang/build/blob/master/docs/faq.md#how-can-i-resolve-ski
   if (result.exitCode == 0 && await wasmOutputFile.exists()) {
     log.info('${result.stdout}\n${result.stderr}');
 
-    await scratchSpace.copyOutput(
-        dartEntrypointId.changeExtension(wasmExtension), buildStep);
+    await scratchSpace.copyOutput(wasmOutputId, buildStep);
+
+    await fixAndCopySourceMap(
+        dartEntrypointId.changeExtension(wasmSourceMapExtension),
+        scratchSpace,
+        buildStep);
 
     final loaderContents = await scratchSpace
         .fileFor(dartEntrypointId.changeExtension(moduleJsExtension))

build_web_compilers/lib/src/dev_compiler_builder.dart

@@ -264,22 +264,17 @@ Future<void> _createDevCompilerModule(
     }
 
     if (debugMode) {
-      // We need to modify the sources in the sourcemap to remove the custom
-      // `multiRootScheme` that we use.
-      var sourceMapId =
-          module.primarySource.changeExtension(jsSourceMapExtension);
-      var file = scratchSpace.fileFor(sourceMapId);
-      var content = await file.readAsString();
-      var json = jsonDecode(content) as Map<String, Object?>;
-      json['sources'] = fixSourceMapSources((json['sources'] as List).cast());
-      await buildStep.writeAsString(sourceMapId, jsonEncode(json));
+      await fixAndCopySourceMap(
+          module.primarySource.changeExtension(jsSourceMapExtension),
+          scratchSpace,
+          buildStep);
 
       // Copy the metadata output, modifying its contents to remove the temp
       // directory from paths
       var metadataId = module.primarySource.changeExtension(metadataExtension);
-      file = scratchSpace.fileFor(metadataId);
-      content = await file.readAsString();
-      json = jsonDecode(content) as Map<String, Object?>;
+      var file = scratchSpace.fileFor(metadataId);
+      var content = await file.readAsString();
+      var json = jsonDecode(content) as Map<String, Object?>;
       _fixMetadataSources(json, scratchSpace.tempDir.uri);
       await buildStep.writeAsString(metadataId, jsonEncode(json));
 

build_web_compilers/lib/src/sdk_js_compile_builder.dart

@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:convert';
 import 'dart:io';
 
 import 'package:bazel_worker/bazel_worker.dart';
@@ -124,12 +123,7 @@ Future<void> _createDevCompilerModule(
 
   // Copy the output back using the buildStep.
   await scratchSpace.copyOutput(jsOutputId, buildStep);
-  // We need to modify the sources in the sourcemap to remove the custom
-  // `multiRootScheme` that we use.
-  var sourceMapId = jsOutputId.changeExtension(_jsSourceMapExtension);
-  var file = scratchSpace.fileFor(sourceMapId);
-  var content = await file.readAsString();
-  var json = jsonDecode(content) as Map<String, Object?>;
-  json['sources'] = fixSourceMapSources((json['sources'] as List).cast());
-  await buildStep.writeAsString(sourceMapId, jsonEncode(json));
+
+  await fixAndCopySourceMap(jsOutputId.changeExtension(_jsSourceMapExtension),
+      scratchSpace, buildStep);
 }

build_web_compilers/lib/src/web_entrypoint_builder.dart

@@ -19,6 +19,7 @@ import 'dev_compiler_bootstrap.dart';
 const ddcBootstrapExtension = '.dart.bootstrap.js';
 const jsEntrypointExtension = '.dart.js';
 const wasmExtension = '.wasm';
+const wasmSourceMapExtension = '.wasm.map';
 const moduleJsExtension = '.mjs';
 const jsEntrypointSourceMapExtension = '.dart.js.map';
 const jsEntrypointArchiveExtension = '.dart.js.tar.gz';
@@ -244,6 +245,7 @@ final class EntrypointBuilderOptions {
         if (optionsFor(WebCompiler.Dart2Wasm) case final dart2wasm?) ...[
           dart2wasm.extension,
           wasmExtension,
+          wasmSourceMapExtension,
         ],
         if (loaderExtension case final loader?) loader,
       ]

build_web_compilers/pubspec.yaml

@@ -1,5 +1,5 @@
 name: build_web_compilers
-version: 4.1.0-beta.1
+version: 4.1.0-beta.2
 description: Builder implementations wrapping the dart2js and DDC compilers.
 repository: https://github.com/dart-lang/build/tree/master/build_web_compilers
 # This package can't be part of the workspace because it requires a very recent