[dart2wasm] Generate source maps

This implements generating source maps for the generated Wasm files.

Copying dart2js's command line interface, a source map file with the
name `<program name>.wasm.map` is generated unless `--no-source-maps` is
passed.

When a source map is generated, the generated .wasm file gets a new
section `sourceMappingURL` with the contents `<program name>.wasm.map`.

This section seems to be undocumented, but Chrome and binaryen recognize
it as the URI to the source map file. Chrome is then loads it
automatically in the DevTools.

## Implementation

- `wasm_builder` package is updated with the new `source_map` library,
  which describes the source mapping entries.

- `wasm_builder`'s `InstructionsBuilder` is updated with the new public
  members:

  - `startSourceMapping`: starts mapping the instructions generated to
    the given source code.

  - `stopSourceMapping`: stops mapping the instructions generated to a
    source code. These instructions won't have a mapping in the source
    map.

- `CodeGenerator` sets the source file URI and location in the file
  when:

  - Starting compiling a new member
  - Compiling an expression and statement

Change-Id: Ic8f723f7a154402c0d34710689db57d640b83b86
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/370500
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Ömer Ağacan <omersa@google.com>

pkg/dart2wasm/lib/closures.dart

@@ -947,8 +947,9 @@ class ClosureRepresentationCluster {
 class Lambda {
   final FunctionNode functionNode;
   final w.FunctionBuilder function;
+  final Source functionNodeSource;
 
-  Lambda(this.functionNode, this.function);
+  Lambda(this.functionNode, this.function, this.functionNodeSource);
 }
 
 /// The context for one or more closures, containing their captured variables.
@@ -1137,12 +1138,22 @@ class CaptureFinder extends RecursiveVisitor {
 
   int get depth => functionIsSyncStarOrAsync.length - 1;
 
-  CaptureFinder(this.closures, this.member);
+  CaptureFinder(this.closures, this.member)
+      : _currentSource =
+            member.enclosingComponent!.uriToSource[member.fileUri]!;
 
   Translator get translator => closures.translator;
 
   w.ModuleBuilder get m => translator.m;
 
+  Source _currentSource;
+
+  @override
+  void visitFileUriExpression(FileUriExpression node) {
+    _currentSource = node.enclosingComponent!.uriToSource[node.fileUri]!;
+    super.visitFileUriExpression(node);
+  }
+
   @override
   void visitFunctionNode(FunctionNode node) {
     assert(depth == 0); // Nested function nodes are skipped by [_visitLambda].
@@ -1275,7 +1286,7 @@ class CaptureFinder extends RecursiveVisitor {
       functionName = "$member closure $functionNodeName at ${node.location}";
     }
     final function = m.functions.define(type, functionName);
-    closures.lambdas[node] = Lambda(node, function);
+    closures.lambdas[node] = Lambda(node, function, _currentSource);
 
     functionIsSyncStarOrAsync.add(node.asyncMarker == AsyncMarker.SyncStar ||
         node.asyncMarker == AsyncMarker.Async);

pkg/dart2wasm/lib/code_generator.dart

@@ -159,6 +159,67 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
     return expectedType;
   }
 
+  Source? _sourceMapSource;
+  int _sourceMapFileOffset = TreeNode.noOffset;
+
+  /// Update the [Source] for the AST nodes being compiled.
+  ///
+  /// The [Source] is used to resolve [TreeNode.fileOffset]s to file URI, line,
+  /// and column numbers, to be able to generate source mappings, in
+  /// [setSourceMapFileOffset].
+  ///
+  /// Setting this `null` disables source mapping for the instructions being
+  /// generated.
+  ///
+  /// This should be called before [setSourceMapFileOffset] as the file offset
+  /// passed to that function is resolved using the [Source].
+  ///
+  /// Returns the old [Source], which can be used to restore the source mapping
+  /// after visiting a sub-tree.
+  Source? setSourceMapSource(Source? source) {
+    final old = _sourceMapSource;
+    _sourceMapSource = source;
+    return old;
+  }
+
+  /// Update the source location of the AST nodes being compiled in the source
+  /// map.
+  ///
+  /// When the offset is [TreeNode.noOffset], this disables mapping the
+  /// generated instructions.
+  ///
+  /// Returns the old file offset, which can be used to restore the source
+  /// mapping after vising a sub-tree.
+  int setSourceMapFileOffset(int fileOffset) {
+    if (!b.recordSourceMaps) {
+      final old = _sourceMapFileOffset;
+      _sourceMapFileOffset = fileOffset;
+      return old;
+    }
+    if (fileOffset == TreeNode.noOffset) {
+      b.stopSourceMapping();
+      final old = _sourceMapFileOffset;
+      _sourceMapFileOffset = fileOffset;
+      return old;
+    }
+    final source = _sourceMapSource!;
+    final fileUri = source.fileUri!;
+    final location = source.getLocation(fileUri, fileOffset);
+    final old = _sourceMapFileOffset;
+    _sourceMapFileOffset = fileOffset;
+    b.startSourceMapping(
+        fileUri, location.line - 1, location.column - 1, member.name.text);
+    return old;
+  }
+
+  /// Calls [setSourceMapSource] and [setSourceMapFileOffset].
+  (Source?, int) setSourceMapSourceAndFileOffset(
+      Source? source, int fileOffset) {
+    final oldSource = setSourceMapSource(source);
+    final oldFileOffset = setSourceMapFileOffset(fileOffset);
+    return (oldSource, oldFileOffset);
+  }
+
   /// Generate code for the member.
   void generate() {
     Member member = this.member;
@@ -208,6 +269,9 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
       return;
     }
 
+    final source = member.enclosingComponent!.uriToSource[member.fileUri]!;
+    setSourceMapSourceAndFileOffset(source, member.fileOffset);
+
     if (member is Constructor) {
       translator.membersBeingGenerated.add(member);
       if (reference.isConstructorBodyReference) {
@@ -484,12 +548,18 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
 
     for (Field field in info.cls!.fields) {
       if (field.isInstanceMember && field.initializer != null) {
+        final source = field.enclosingComponent!.uriToSource[field.fileUri]!;
+        final (oldSource, oldFileOffset) =
+            setSourceMapSourceAndFileOffset(source, field.fileOffset);
+
         int fieldIndex = translator.fieldIndex[field]!;
         w.Local local = addLocal(info.struct.fields[fieldIndex].type.unpacked);
 
         wrap(field.initializer!, info.struct.fields[fieldIndex].type.unpacked);
         b.local_set(local);
         fieldLocals[field] = local;
+
+        setSourceMapSourceAndFileOffset(oldSource, oldFileOffset);
       }
     }
   }
@@ -717,6 +787,8 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
     // Initialize closure information from enclosing member.
     this.closures = closures;
 
+    setSourceMapSource(lambda.functionNodeSource);
+
     assert(lambda.functionNode.asyncMarker != AsyncMarker.Async);
 
     setupLambdaParametersAndContexts(lambda);
@@ -877,22 +949,39 @@ class CodeGenerator extends ExpressionVisitor1<w.ValueType, w.ValueType>
   /// result to the expected type if needed. All expression code generation goes
   /// through this method.
   w.ValueType wrap(Expression node, w.ValueType expectedType) {
+    var sourceUpdated = false;
+    Source? oldSource;
+    if (node is FileUriNode) {
+      final source =
+          node.enclosingComponent!.uriToSource[(node as FileUriNode).fileUri]!;
+      oldSource = setSourceMapSource(source);
+      sourceUpdated = true;
+    }
+    final oldFileOffset = setSourceMapFileOffset(node.fileOffset);
     try {
       w.ValueType resultType = node.accept1(this, expectedType);
       translator.convertType(function, resultType, expectedType);
       return expectedType;
     } catch (_) {
       _printLocation(node);
       rethrow;
+    } finally {
+      if (sourceUpdated) {
+        setSourceMapSource(oldSource);
+      }
+      setSourceMapFileOffset(oldFileOffset);
     }
   }
 
   void visitStatement(Statement node) {
+    final oldFileOffset = setSourceMapFileOffset(node.fileOffset);
     try {
       node.accept(this);
     } catch (_) {
       _printLocation(node);
       rethrow;
+    } finally {
+      setSourceMapFileOffset(oldFileOffset);
     }
   }
 

pkg/dart2wasm/lib/compile.dart

@@ -33,7 +33,7 @@ import 'package:vm/transformations/type_flow/transformer.dart' as globalTypeFlow
     show transformComponent;
 import 'package:vm/transformations/unreachable_code_elimination.dart'
     as unreachable_code_elimination;
-import 'package:wasm_builder/wasm_builder.dart' show Module, Serializer;
+import 'package:wasm_builder/wasm_builder.dart' show Serializer;
 
 import 'compiler_options.dart' as compiler;
 import 'constant_evaluator.dart';
@@ -45,26 +45,26 @@ import 'target.dart' hide Mode;
 import 'translator.dart';
 
 class CompilerOutput {
-  final Module _wasmModule;
+  final Uint8List wasmModule;
   final String jsRuntime;
+  final String? sourceMap;
 
-  late final Uint8List wasmModule = _serializeWasmModule();
-
-  Uint8List _serializeWasmModule() {
-    final s = Serializer();
-    _wasmModule.serialize(s);
-    return s.data;
-  }
-
-  CompilerOutput(this._wasmModule, this.jsRuntime);
+  CompilerOutput(this.wasmModule, this.jsRuntime, this.sourceMap);
 }
 
 /// Compile a Dart file into a Wasm module.
 ///
 /// Returns `null` if an error occurred during compilation. The
 /// [handleDiagnosticMessage] callback will have received an error message
 /// describing the error.
-Future<CompilerOutput?> compileToModule(compiler.WasmCompilerOptions options,
+///
+/// When generating a source map, `sourceMapUrl` argument should be provided
+/// with the URL of the source map. This value will be added to the Wasm module
+/// in `sourceMappingURL` section. When this argument is null the code
+/// generator does not generate source mappings.
+Future<CompilerOutput?> compileToModule(
+    compiler.WasmCompilerOptions options,
+    Uri? sourceMapUrl,
     void Function(DiagnosticMessage) handleDiagnosticMessage) async {
   var succeeded = true;
   void diagnosticMessageHandler(DiagnosticMessage message) {
@@ -205,10 +205,19 @@ Future<CompilerOutput?> compileToModule(compiler.WasmCompilerOptions options,
         depFile);
   }
 
-  final wasmModule = translator.translate();
+  final generateSourceMaps = options.translatorOptions.generateSourceMaps;
+  final wasmModule = translator.translate(sourceMapUrl);
+  final serializer = Serializer();
+  wasmModule.serialize(serializer);
+  final wasmModuleSerialized = serializer.data;
+
+  final sourceMap =
+      generateSourceMaps ? serializer.sourceMapSerializer.serialize() : null;
+
   String jsRuntime = jsRuntimeFinalizer.generate(
       translator.functions.translatedProcedures,
       translator.internalizedStringsForJSRuntime,
       mode);
-  return CompilerOutput(wasmModule, jsRuntime);
+
+  return CompilerOutput(wasmModuleSerialized, jsRuntime, sourceMap);
 }

pkg/dart2wasm/lib/dart2wasm.dart

@@ -94,6 +94,10 @@ final List<Option> options = [
   Flag("enable-experimental-ffi",
       (o, value) => o.translatorOptions.enableExperimentalFfi = value,
       defaultsTo: _d.translatorOptions.enableExperimentalFfi),
+  // Use same flag with dart2js for disabling source maps.
+  Flag("no-source-maps",
+      (o, value) => o.translatorOptions.generateSourceMaps = !value,
+      defaultsTo: !_d.translatorOptions.generateSourceMaps),
 ];
 
 Map<fe.ExperimentalFlag, bool> processFeExperimentalFlags(

pkg/dart2wasm/lib/generate_wasm.dart

@@ -5,6 +5,7 @@
 import 'dart:io';
 
 import 'package:front_end/src/api_unstable/vm.dart' show printDiagnosticMessage;
+import 'package:path/path.dart' as path;
 
 import 'compile.dart';
 import 'compiler_options.dart';
@@ -22,10 +23,16 @@ Future<int> generateWasm(WasmCompilerOptions options,
     print('  - librariesSpecPath = ${options.librariesSpecPath}');
     print('  - packagesPath file = ${options.packagesPath}');
     print('  - platformPath file = ${options.platformPath}');
+    print(
+        '  - generate source maps = ${options.translatorOptions.generateSourceMaps}');
   }
 
-  CompilerOutput? output = await compileToModule(
-      options, (message) => printDiagnosticMessage(message, errorPrinter));
+  final relativeSourceMapUrl = options.translatorOptions.generateSourceMaps
+      ? Uri.file('${path.basename(options.outputFile)}.map')
+      : null;
+
+  CompilerOutput? output = await compileToModule(options, relativeSourceMapUrl,
+      (message) => printDiagnosticMessage(message, errorPrinter));
 
   if (output == null) {
     return 1;
@@ -36,8 +43,13 @@ Future<int> generateWasm(WasmCompilerOptions options,
   await outFile.writeAsBytes(output.wasmModule);
 
   final jsFile = options.outputJSRuntimeFile ??
-      '${options.outputFile.substring(0, options.outputFile.lastIndexOf('.'))}.mjs';
+      path.setExtension(options.outputFile, '.mjs');
   await File(jsFile).writeAsString(output.jsRuntime);
 
+  final sourceMap = output.sourceMap;
+  if (sourceMap != null) {
+    await File('${options.outputFile}.map').writeAsString(sourceMap);
+  }
+
   return 0;
 }

pkg/dart2wasm/lib/state_machine.dart

@@ -606,6 +606,9 @@ abstract class StateMachineCodeGenerator extends CodeGenerator {
 
   @override
   void generate() {
+    final source = member.enclosingComponent!.uriToSource[member.fileUri]!;
+    setSourceMapSource(source);
+    setSourceMapFileOffset(member.fileOffset);
     closures = Closures(translator, member);
     setupParametersAndContexts(member.reference);
     _generateBodies(member.function!);
@@ -614,6 +617,7 @@ abstract class StateMachineCodeGenerator extends CodeGenerator {
   @override
   w.BaseFunction generateLambda(Lambda lambda, Closures closures) {
     this.closures = closures;
+    setSourceMapSource(lambda.functionNodeSource);
     setupLambdaParametersAndContexts(lambda);
     _generateBodies(lambda.functionNode);
     return function;

pkg/dart2wasm/lib/translator.dart

@@ -46,6 +46,7 @@ class TranslatorOptions {
   bool verbose = false;
   bool enableExperimentalFfi = false;
   bool enableExperimentalWasmInterop = false;
+  bool generateSourceMaps = true;
   int inliningLimit = 0;
   int? sharedMemoryMaxPages;
   List<int> watchPoints = [];
@@ -292,8 +293,8 @@ class Translator with KernelNodes {
     dynamicForwarders = DynamicForwarders(this);
   }
 
-  w.Module translate() {
-    m = w.ModuleBuilder(watchPoints: options.watchPoints);
+  w.Module translate(Uri? sourceMapUrl) {
+    m = w.ModuleBuilder(sourceMapUrl, watchPoints: options.watchPoints);
     voidMarker = w.RefType.def(w.StructType("void"), nullable: true);
 
     // Collect imports and exports as the very first thing so the function types

pkg/dart2wasm/pubspec.yaml

@@ -15,6 +15,7 @@ dependencies:
   kernel: any
   vm: any
   wasm_builder: any
+  path: any
 
 # Use 'any' constraints here; we get our versions from the DEPS file.
 dev_dependencies:

pkg/test_runner/lib/src/test_suite.dart

@@ -838,6 +838,10 @@ class StandardTestSuite extends TestSuite {
         for (var opt in vmOptions)
           opt.replaceAll(r'$TEST_COMPILATION_DIR', tempDir)
       ];
+      for (var i = 0; i < testFile.dart2wasmOptions.length; i += 1) {
+        testFile.dart2wasmOptions[i] = testFile.dart2wasmOptions[i]
+            .replaceAll(r'$TEST_COMPILATION_DIR', tempDir);
+      }
       environment['TEST_COMPILATION_DIR'] = tempDir;
 
       compileTimeArguments = compilerConfiguration.computeCompilerArguments(