pkg/compiler/lib/src/io/source_map_builder.dart - sdk - Git at Google

 // Copyright (c) 2012, 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.

 library dart2js.source_map_builder;

 import 'package:front_end/src/api_unstable/dart2js.dart' as fe;
 import 'package:kernel/ast.dart' show Location;
 import '../../compiler.dart' show CompilerOutput, OutputSink, OutputType;
 import '../util/util.dart';
 import 'location_provider.dart';
 import 'code_output.dart' show SourceLocationsProvider, SourceLocations;
 import 'source_information.dart' show SourceLocation, FrameEntry;

 class SourceMapBuilder {
   final String version;

   /// The URI of the source map file.
   final Uri sourceMapUri;

   /// The URI of the target language file.
   final Uri targetFileUri;

   final LocationProvider locationProvider;
   final List<SourceMapEntry> entries = [];

   /// Extension used to deobfuscate minified names in error messages.
   final Map<String, String> minifiedGlobalNames;
   final Map<String, String> minifiedInstanceNames;

   /// Extension used to deobfuscate inlined stack frames.
   final Map<int, List<FrameEntry>> frames;

   SourceMapBuilder(
       this.version,
       this.sourceMapUri,
       this.targetFileUri,
       this.locationProvider,
       this.minifiedGlobalNames,
       this.minifiedInstanceNames,
       this.frames);

   void addMapping(int targetOffset, SourceLocation sourceLocation) {
     entries.add(SourceMapEntry(sourceLocation, targetOffset));
   }

   void printStringListOn(Iterable<String> strings, StringBuffer buffer) {
     bool first = true;
     buffer.write('[');
     for (String string in strings) {
       if (!first) buffer.write(',');
       buffer.write('"');
       writeJsonEscapedCharsOn(string, buffer);
       buffer.write('"');
       first = false;
     }
     buffer.write(']');
   }

   String build() {
     LineColumnMap<SourceMapEntry> lineColumnMap = LineColumnMap();
     Map<Uri, LineColumnMap<SourceMapEntry>> sourceLocationMap = {};
     entries.forEach((SourceMapEntry sourceMapEntry) {
       Location kernelLocation =
           locationProvider.getLocation(sourceMapEntry.targetOffset);
       int line = kernelLocation.line - 1;
       int column = kernelLocation.column - 1;
       lineColumnMap.add(line, column, sourceMapEntry);

       SourceLocation location = sourceMapEntry.sourceLocation;
       if (location != null) {
         if (location.sourceUri != null) {
           LineColumnMap<SourceMapEntry> sourceLineColumnMap =
               sourceLocationMap.putIfAbsent(
                   location.sourceUri, () => LineColumnMap<SourceMapEntry>());
           sourceLineColumnMap.add(
               location.line - 1, location.column - 1, sourceMapEntry);
         }
       }
     });

     return _build(lineColumnMap);
   }

   String _build(LineColumnMap<SourceMapEntry> lineColumnMap) {
     IndexMap<Uri> uriMap = IndexMap<Uri>();
     IndexMap<String> nameMap = IndexMap<String>();

     void registerLocation(SourceLocation sourceLocation) {
       if (sourceLocation != null) {
         if (sourceLocation.sourceUri != null) {
           uriMap.register(sourceLocation.sourceUri);
           if (sourceLocation.sourceName != null) {
             nameMap.register(sourceLocation.sourceName);
           }
         }
       }
     }

     lineColumnMap.forEachElement((SourceMapEntry entry) {
       registerLocation(entry.sourceLocation);
     });

     minifiedGlobalNames.values.forEach(nameMap.register);
     minifiedInstanceNames.values.forEach(nameMap.register);
     for (List<FrameEntry> entries in frames.values) {
       for (var frame in entries) {
         registerLocation(frame.pushLocation);
         if (frame.inlinedMethodName != null) {
           nameMap.register(frame.inlinedMethodName);
         }
       }
     }

     StringBuffer mappingsBuffer = StringBuffer();
     writeEntries(lineColumnMap, uriMap, nameMap, mappingsBuffer);

     StringBuffer buffer = StringBuffer();
     buffer.write('{\n');
     buffer.write('  "version": 3,\n');
     buffer.write('  "engine": "$version",\n');
     if (sourceMapUri != null && targetFileUri != null) {
       buffer.write('  "file": '
           '"${fe.relativizeUri(sourceMapUri, targetFileUri, false)}",\n');
     }
     buffer.write('  "sourceRoot": "",\n');
     buffer.write('  "sources": ');
     Iterable<String> relativeSourceUriList = const <String>[];
     if (sourceMapUri != null) {
       relativeSourceUriList =
           uriMap.elements.map((u) => fe.relativizeUri(sourceMapUri, u, false));
     }
     printStringListOn(relativeSourceUriList, buffer);
     buffer.write(',\n');
     buffer.write('  "names": ');
     printStringListOn(nameMap.elements, buffer);
     buffer.write(',\n');
     buffer.write('  "mappings": "');
     buffer.write(mappingsBuffer);
     buffer.write('",\n');
     buffer.write('  "x_org_dartlang_dart2js": {\n');
     buffer.write('    "minified_names": {\n');
     buffer.write('      "global": ');
     writeMinifiedNames(minifiedGlobalNames, nameMap, buffer);
     buffer.write(',\n');
     buffer.write('      "instance": ');
     writeMinifiedNames(minifiedInstanceNames, nameMap, buffer);
     buffer.write('\n    },\n');
     buffer.write('    "frames": ');
     writeFrames(uriMap, nameMap, buffer);
     buffer.write('\n  }\n}\n');
     return buffer.toString();
   }

   void writeEntries(LineColumnMap<SourceMapEntry> entries, IndexMap<Uri> uriMap,
       IndexMap<String> nameMap, StringBuffer output) {
     SourceLocation previousSourceLocation;
     int previousTargetLine = 0;
     DeltaEncoder targetColumnEncoder = DeltaEncoder();
     bool firstEntryInLine = true;
     DeltaEncoder sourceUriIndexEncoder = DeltaEncoder();
     DeltaEncoder sourceLineEncoder = DeltaEncoder();
     DeltaEncoder sourceColumnEncoder = DeltaEncoder();
     DeltaEncoder sourceNameIndexEncoder = DeltaEncoder();

     entries.forEach((int targetLine, int targetColumn, SourceMapEntry entry) {
       SourceLocation sourceLocation = entry.sourceLocation;
       if (sourceLocation == previousSourceLocation) {
         return;
       }

       if (targetLine > previousTargetLine) {
         for (int i = previousTargetLine; i < targetLine; ++i) {
           output.write(';');
         }
         previousTargetLine = targetLine;
         previousSourceLocation = null;
         targetColumnEncoder.reset();
         firstEntryInLine = true;
       }

       if (!firstEntryInLine) {
         output.write(',');
       }
       firstEntryInLine = false;

       targetColumnEncoder.encode(output, targetColumn);

       if (sourceLocation == null) {
         return;
       }

       Uri sourceUri = sourceLocation.sourceUri;
       if (sourceUri != null) {
         sourceUriIndexEncoder.encode(output, uriMap[sourceUri]);
         sourceLineEncoder.encode(output, sourceLocation.line - 1);
         sourceColumnEncoder.encode(output, sourceLocation.column - 1);
       }

       String sourceName = sourceLocation.sourceName;
       if (sourceName != null) {
         sourceNameIndexEncoder.encode(output, nameMap[sourceName]);
       }

       previousSourceLocation = sourceLocation;
     });
   }

   void writeMinifiedNames(Map<String, String> minifiedNames,
       IndexMap<String> nameMap, StringBuffer buffer) {
     bool first = true;
     buffer.write('"');
     minifiedNames.forEach((String minifiedName, String name) {
       if (!first) buffer.write(',');
       // minifiedNames are valid JS identifiers so they don't need to be escaped
       buffer.write(minifiedName);
       buffer.write(',');
       buffer.write(nameMap[name]);
       first = false;
     });
     buffer.write('"');
   }

   void writeFrames(
       IndexMap<Uri> uriMap, IndexMap<String> nameMap, StringBuffer buffer) {
     var offsetEncoder = DeltaEncoder();
     var uriEncoder = DeltaEncoder();
     var lineEncoder = DeltaEncoder();
     var columnEncoder = DeltaEncoder();
     var nameEncoder = DeltaEncoder();
     buffer.write('"');
     frames.forEach((int offset, List<FrameEntry> entries) {
       for (var entry in entries) {
         offsetEncoder.encode(buffer, offset);
         if (entry.isPush) {
           SourceLocation location = entry.pushLocation;
           uriEncoder.encode(buffer, uriMap[location.sourceUri]);
           lineEncoder.encode(buffer, location.line - 1);
           columnEncoder.encode(buffer, location.column - 1);
           nameEncoder.encode(buffer, nameMap[entry.inlinedMethodName]);
         } else {
           // ; and , are not used by VLQ so we can distinguish them in the
           // encoding, this is the same reason they are used in the mappings
           // field.
           buffer.write(entry.isEmptyPop ? ";" : ",");
         }
       }
     });
     buffer.write('"');
   }

   /// Returns the source map tag to put at the end a .js file in [fileUri] to
   /// make it point to the source map file in [sourceMapUri].
   static String generateSourceMapTag(Uri sourceMapUri, Uri fileUri) {
     if (sourceMapUri != null && fileUri != null) {
       String sourceMapFileName = fe.relativizeUri(fileUri, sourceMapUri, false);
       return '''

 //# sourceMappingURL=$sourceMapFileName
 ''';
     }
     return '';
   }

   /// Generates source map files for all [SourceLocations] in
   /// [sourceLocationsProvider] for the .js code in [locationProvider]
   /// [sourceMapUri] is used to relativizes the URIs of the referenced source
   /// files and the target [fileUri]. [name] and [outputProvider] are used to
   /// create the [OutputSink] for the source map text.
   static void outputSourceMap(
       SourceLocationsProvider sourceLocationsProvider,
       LocationProvider locationProvider,
       Map<String, String> minifiedGlobalNames,
       Map<String, String> minifiedInstanceNames,
       String name,
       Uri sourceMapUri,
       Uri fileUri,
       CompilerOutput compilerOutput) {
     // Create a source file for the compilation output. This allows using
     // [:getLine:] to transform offsets to line numbers in [SourceMapBuilder].
     int index = 0;
     sourceLocationsProvider.sourceLocations
         .forEach((SourceLocations sourceLocations) {
       SourceMapBuilder sourceMapBuilder = SourceMapBuilder(
           sourceLocations.name,
           sourceMapUri,
           fileUri,
           locationProvider,
           minifiedGlobalNames,
           minifiedInstanceNames,
           sourceLocations.frameMarkers);
       sourceLocations.forEachSourceLocation(sourceMapBuilder.addMapping);
       String sourceMap = sourceMapBuilder.build();
       String extension = 'js.map';
       if (index > 0) {
         if (name == '') {
           name = fileUri != null ? fileUri.pathSegments.last : 'out.js';
           extension = 'map.${sourceLocations.name}';
         } else {
           extension = 'js.map.${sourceLocations.name}';
         }
       }
       compilerOutput.createOutputSink(name, extension, OutputType.sourceMap)
         ..add(sourceMap)
         ..close();
       index++;
     });
   }
 }

 /// Encoder for value deltas in VLQ format.
 class DeltaEncoder {
   /// The last emitted value of the encoder.
   int _value = 0;

   /// Reset the encoder to its initial state.
   void reset() {
     _value = 0;
   }

   /// Writes the VLQ of delta between [value] and the last emitted value into
   /// [output] and updates the last emitted value of the encoder.
   void encode(StringBuffer output, int value) {
     _value = encodeVLQ(output, value, _value);
   }

   static const int VLQ_BASE_SHIFT = 5;
   static const int VLQ_BASE_MASK = (1 << 5) - 1;
   static const int VLQ_CONTINUATION_BIT = 1 << 5;
   static const int VLQ_CONTINUATION_MASK = 1 << 5;
   static const String BASE64_DIGITS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn'
       'opqrstuvwxyz0123456789+/';

   /// Writes the VLQ of delta between [value] and [offset] into [output] and
   /// return [value].
   static int encodeVLQ(StringBuffer output, int value, int offset) {
     int delta = value - offset;
     int signBit = 0;
     if (delta < 0) {
       signBit = 1;
       delta = -delta;
     }
     delta = (delta << 1) | signBit;
     do {
       int digit = delta & VLQ_BASE_MASK;
       delta >>= VLQ_BASE_SHIFT;
       if (delta > 0) {
         digit |= VLQ_CONTINUATION_BIT;
       }
       output.write(BASE64_DIGITS[digit]);
     } while (delta > 0);
     return value;
   }
 }

 class SourceMapEntry {
   SourceLocation sourceLocation;
   int targetOffset;

   SourceMapEntry(this.sourceLocation, this.targetOffset);
 }

 /// Map from line/column pairs to lists of [T] elements.
 class LineColumnMap<T> {
   final Map<int, Map<int, List<T>>> _map = {};

   /// Returns the list of elements associated with ([line],[column]).
   List<T> _getList(int line, int column) {
     Map<int, List<T>> lineMap = _map[line] ??= {};
     return lineMap[column] ??= [];
   }

   /// Adds [element] to the end of the list of elements associated with
   /// ([line],[column]).
   void add(int line, int column, T element) {
     _getList(line, column).add(element);
   }

   /// Adds [element] to the beginning of the list of elements associated with
   /// ([line],[column]).
   void addFirst(int line, int column, T element) {
     _getList(line, column).insert(0, element);
   }

   /// Calls [f] with the line number for each line with associated elements.
   ///
   /// [f] is called in increasing line order.
   void forEachLine(f(int line)) {
     List<int> lines = _map.keys.toList()..sort();
     lines.forEach(f);
   }

   /// Returns the elements for the first the column in [line] that has
   /// associated elements.
   List<T> getFirstElementsInLine(int line) {
     Map<int, List<T>> lineMap = _map[line];
     if (lineMap == null) return null;
     List<int> columns = lineMap.keys.toList()..sort();
     return lineMap[columns.first];
   }

   /// Calls [f] for each column with associated elements in [line].
   ///
   /// [f] is called in increasing column order.
   void forEachColumn(int line, f(int column, List<T> elements)) {
     Map<int, List<T>> lineMap = _map[line];
     if (lineMap != null) {
       List<int> columns = lineMap.keys.toList()..sort();
       columns.forEach((int column) {
         f(column, lineMap[column]);
       });
     }
   }

   /// Calls [f] for each line/column/element triplet in the map.
   ///
   /// [f] is called in increasing line, column, element order.
   void forEach(f(int line, int column, T element)) {
     List<int> lines = _map.keys.toList()..sort();
     for (int line in lines) {
       Map<int, List<T>> lineMap = _map[line];
       List<int> columns = lineMap.keys.toList()..sort();
       for (int column in columns) {
         lineMap[column].forEach((e) => f(line, column, e));
       }
     }
   }

   /// Calls [f] for each element associated in the map.
   ///
   /// [f] is called in increasing line, column, element order.
   void forEachElement(f(T element)) {
     forEach((line, column, element) => f(element));
   }
 }

 /// Map from [T] elements to assigned indices.
 class IndexMap<T> {
   Map<T, int> map = {};

   /// Register [element] and returns its index.
   int register(T element) {
     return map.putIfAbsent(element, () => map.length);
   }

   /// Returns the index of [element].
   int operator [](T element) => map[element];

   /// Returns the indexed elements.
   Iterable<T> get elements => map.keys;
 }
	// Copyright (c) 2012, 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.

	library dart2js.source_map_builder;

	import 'package:front_end/src/api_unstable/dart2js.dart' as fe;
	import 'package:kernel/ast.dart' show Location;
	import '../../compiler.dart' show CompilerOutput, OutputSink, OutputType;
	import '../util/util.dart';
	import 'location_provider.dart';
	import 'code_output.dart' show SourceLocationsProvider, SourceLocations;
	import 'source_information.dart' show SourceLocation, FrameEntry;

	class SourceMapBuilder {
	final String version;

	/// The URI of the source map file.
	final Uri sourceMapUri;

	/// The URI of the target language file.
	final Uri targetFileUri;

	final LocationProvider locationProvider;
	final List<SourceMapEntry> entries = [];

	/// Extension used to deobfuscate minified names in error messages.
	final Map<String, String> minifiedGlobalNames;
	final Map<String, String> minifiedInstanceNames;

	/// Extension used to deobfuscate inlined stack frames.
	final Map<int, List<FrameEntry>> frames;

	SourceMapBuilder(
	this.version,
	this.sourceMapUri,
	this.targetFileUri,
	this.locationProvider,
	this.minifiedGlobalNames,
	this.minifiedInstanceNames,
	this.frames);

	void addMapping(int targetOffset, SourceLocation sourceLocation) {
	entries.add(SourceMapEntry(sourceLocation, targetOffset));
	}

	void printStringListOn(Iterable<String> strings, StringBuffer buffer) {
	bool first = true;
	buffer.write('[');
	for (String string in strings) {
	if (!first) buffer.write(',');
	buffer.write('"');
	writeJsonEscapedCharsOn(string, buffer);
	buffer.write('"');
	first = false;
	}
	buffer.write(']');
	}

	String build() {
	LineColumnMap<SourceMapEntry> lineColumnMap = LineColumnMap();
	Map<Uri, LineColumnMap<SourceMapEntry>> sourceLocationMap = {};
	entries.forEach((SourceMapEntry sourceMapEntry) {
	Location kernelLocation =
	locationProvider.getLocation(sourceMapEntry.targetOffset);
	int line = kernelLocation.line - 1;
	int column = kernelLocation.column - 1;
	lineColumnMap.add(line, column, sourceMapEntry);

	SourceLocation location = sourceMapEntry.sourceLocation;
	if (location != null) {
	if (location.sourceUri != null) {
	LineColumnMap<SourceMapEntry> sourceLineColumnMap =
	sourceLocationMap.putIfAbsent(
	location.sourceUri, () => LineColumnMap<SourceMapEntry>());
	sourceLineColumnMap.add(
	location.line - 1, location.column - 1, sourceMapEntry);
	}
	}
	});

	return _build(lineColumnMap);
	}

	String _build(LineColumnMap<SourceMapEntry> lineColumnMap) {
	IndexMap<Uri> uriMap = IndexMap<Uri>();
	IndexMap<String> nameMap = IndexMap<String>();

	void registerLocation(SourceLocation sourceLocation) {
	if (sourceLocation != null) {
	if (sourceLocation.sourceUri != null) {
	uriMap.register(sourceLocation.sourceUri);
	if (sourceLocation.sourceName != null) {
	nameMap.register(sourceLocation.sourceName);
	}
	}
	}
	}

	lineColumnMap.forEachElement((SourceMapEntry entry) {
	registerLocation(entry.sourceLocation);
	});

	minifiedGlobalNames.values.forEach(nameMap.register);
	minifiedInstanceNames.values.forEach(nameMap.register);
	for (List<FrameEntry> entries in frames.values) {
	for (var frame in entries) {
	registerLocation(frame.pushLocation);
	if (frame.inlinedMethodName != null) {
	nameMap.register(frame.inlinedMethodName);
	}
	}
	}

	StringBuffer mappingsBuffer = StringBuffer();
	writeEntries(lineColumnMap, uriMap, nameMap, mappingsBuffer);

	StringBuffer buffer = StringBuffer();
	buffer.write('{\n');
	buffer.write(' "version": 3,\n');
	buffer.write(' "engine": "$version",\n');
	if (sourceMapUri != null && targetFileUri != null) {
	buffer.write(' "file": '
	'"${fe.relativizeUri(sourceMapUri, targetFileUri, false)}",\n');
	}
	buffer.write(' "sourceRoot": "",\n');
	buffer.write(' "sources": ');
	Iterable<String> relativeSourceUriList = const <String>[];
	if (sourceMapUri != null) {
	relativeSourceUriList =
	uriMap.elements.map((u) => fe.relativizeUri(sourceMapUri, u, false));
	}
	printStringListOn(relativeSourceUriList, buffer);
	buffer.write(',\n');
	buffer.write(' "names": ');
	printStringListOn(nameMap.elements, buffer);
	buffer.write(',\n');
	buffer.write(' "mappings": "');
	buffer.write(mappingsBuffer);
	buffer.write('",\n');
	buffer.write(' "x_org_dartlang_dart2js": {\n');
	buffer.write(' "minified_names": {\n');
	buffer.write(' "global": ');
	writeMinifiedNames(minifiedGlobalNames, nameMap, buffer);
	buffer.write(',\n');
	buffer.write(' "instance": ');
	writeMinifiedNames(minifiedInstanceNames, nameMap, buffer);
	buffer.write('\n },\n');
	buffer.write(' "frames": ');
	writeFrames(uriMap, nameMap, buffer);
	buffer.write('\n }\n}\n');
	return buffer.toString();
	}

	void writeEntries(LineColumnMap<SourceMapEntry> entries, IndexMap<Uri> uriMap,
	IndexMap<String> nameMap, StringBuffer output) {
	SourceLocation previousSourceLocation;
	int previousTargetLine = 0;
	DeltaEncoder targetColumnEncoder = DeltaEncoder();
	bool firstEntryInLine = true;
	DeltaEncoder sourceUriIndexEncoder = DeltaEncoder();
	DeltaEncoder sourceLineEncoder = DeltaEncoder();
	DeltaEncoder sourceColumnEncoder = DeltaEncoder();
	DeltaEncoder sourceNameIndexEncoder = DeltaEncoder();

	entries.forEach((int targetLine, int targetColumn, SourceMapEntry entry) {
	SourceLocation sourceLocation = entry.sourceLocation;
	if (sourceLocation == previousSourceLocation) {
	return;
	}

	if (targetLine > previousTargetLine) {
	for (int i = previousTargetLine; i < targetLine; ++i) {
	output.write(';');
	}
	previousTargetLine = targetLine;
	previousSourceLocation = null;
	targetColumnEncoder.reset();
	firstEntryInLine = true;
	}

	if (!firstEntryInLine) {
	output.write(',');
	}
	firstEntryInLine = false;

	targetColumnEncoder.encode(output, targetColumn);

	if (sourceLocation == null) {
	return;
	}

	Uri sourceUri = sourceLocation.sourceUri;
	if (sourceUri != null) {
	sourceUriIndexEncoder.encode(output, uriMap[sourceUri]);
	sourceLineEncoder.encode(output, sourceLocation.line - 1);
	sourceColumnEncoder.encode(output, sourceLocation.column - 1);
	}

	String sourceName = sourceLocation.sourceName;
	if (sourceName != null) {
	sourceNameIndexEncoder.encode(output, nameMap[sourceName]);
	}

	previousSourceLocation = sourceLocation;
	});
	}

	void writeMinifiedNames(Map<String, String> minifiedNames,
	IndexMap<String> nameMap, StringBuffer buffer) {
	bool first = true;
	buffer.write('"');
	minifiedNames.forEach((String minifiedName, String name) {
	if (!first) buffer.write(',');
	// minifiedNames are valid JS identifiers so they don't need to be escaped
	buffer.write(minifiedName);
	buffer.write(',');
	buffer.write(nameMap[name]);
	first = false;
	});
	buffer.write('"');
	}

	void writeFrames(
	IndexMap<Uri> uriMap, IndexMap<String> nameMap, StringBuffer buffer) {
	var offsetEncoder = DeltaEncoder();
	var uriEncoder = DeltaEncoder();
	var lineEncoder = DeltaEncoder();
	var columnEncoder = DeltaEncoder();
	var nameEncoder = DeltaEncoder();
	buffer.write('"');
	frames.forEach((int offset, List<FrameEntry> entries) {
	for (var entry in entries) {
	offsetEncoder.encode(buffer, offset);
	if (entry.isPush) {
	SourceLocation location = entry.pushLocation;
	uriEncoder.encode(buffer, uriMap[location.sourceUri]);
	lineEncoder.encode(buffer, location.line - 1);
	columnEncoder.encode(buffer, location.column - 1);
	nameEncoder.encode(buffer, nameMap[entry.inlinedMethodName]);
	} else {
	// ; and , are not used by VLQ so we can distinguish them in the
	// encoding, this is the same reason they are used in the mappings
	// field.
	buffer.write(entry.isEmptyPop ? ";" : ",");
	}
	}
	});
	buffer.write('"');
	}

	/// Returns the source map tag to put at the end a .js file in [fileUri] to
	/// make it point to the source map file in [sourceMapUri].
	static String generateSourceMapTag(Uri sourceMapUri, Uri fileUri) {
	if (sourceMapUri != null && fileUri != null) {
	String sourceMapFileName = fe.relativizeUri(fileUri, sourceMapUri, false);
	return '''

	//# sourceMappingURL=$sourceMapFileName
	''';
	}
	return '';
	}

	/// Generates source map files for all [SourceLocations] in
	/// [sourceLocationsProvider] for the .js code in [locationProvider]
	/// [sourceMapUri] is used to relativizes the URIs of the referenced source
	/// files and the target [fileUri]. [name] and [outputProvider] are used to
	/// create the [OutputSink] for the source map text.
	static void outputSourceMap(
	SourceLocationsProvider sourceLocationsProvider,
	LocationProvider locationProvider,
	Map<String, String> minifiedGlobalNames,
	Map<String, String> minifiedInstanceNames,
	String name,
	Uri sourceMapUri,
	Uri fileUri,
	CompilerOutput compilerOutput) {
	// Create a source file for the compilation output. This allows using
	// [:getLine:] to transform offsets to line numbers in [SourceMapBuilder].
	int index = 0;
	sourceLocationsProvider.sourceLocations
	.forEach((SourceLocations sourceLocations) {
	SourceMapBuilder sourceMapBuilder = SourceMapBuilder(
	sourceLocations.name,
	sourceMapUri,
	fileUri,
	locationProvider,
	minifiedGlobalNames,
	minifiedInstanceNames,
	sourceLocations.frameMarkers);
	sourceLocations.forEachSourceLocation(sourceMapBuilder.addMapping);
	String sourceMap = sourceMapBuilder.build();
	String extension = 'js.map';
	if (index > 0) {
	if (name == '') {
	name = fileUri != null ? fileUri.pathSegments.last : 'out.js';
	extension = 'map.${sourceLocations.name}';
	} else {
	extension = 'js.map.${sourceLocations.name}';
	}
	}
	compilerOutput.createOutputSink(name, extension, OutputType.sourceMap)
	..add(sourceMap)
	..close();
	index++;
	});
	}
	}

	/// Encoder for value deltas in VLQ format.
	class DeltaEncoder {
	/// The last emitted value of the encoder.
	int _value = 0;

	/// Reset the encoder to its initial state.
	void reset() {
	_value = 0;
	}

	/// Writes the VLQ of delta between [value] and the last emitted value into
	/// [output] and updates the last emitted value of the encoder.
	void encode(StringBuffer output, int value) {
	_value = encodeVLQ(output, value, _value);
	}

	static const int VLQ_BASE_SHIFT = 5;
	static const int VLQ_BASE_MASK = (1 << 5) - 1;
	static const int VLQ_CONTINUATION_BIT = 1 << 5;
	static const int VLQ_CONTINUATION_MASK = 1 << 5;
	static const String BASE64_DIGITS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn'
	'opqrstuvwxyz0123456789+/';

	/// Writes the VLQ of delta between [value] and [offset] into [output] and
	/// return [value].
	static int encodeVLQ(StringBuffer output, int value, int offset) {
	int delta = value - offset;
	int signBit = 0;
	if (delta < 0) {
	signBit = 1;
	delta = -delta;
	}
	delta = (delta << 1) \| signBit;
	do {
	int digit = delta & VLQ_BASE_MASK;
	delta >>= VLQ_BASE_SHIFT;
	if (delta > 0) {
	digit \|= VLQ_CONTINUATION_BIT;
	}
	output.write(BASE64_DIGITS[digit]);
	} while (delta > 0);
	return value;
	}
	}

	class SourceMapEntry {
	SourceLocation sourceLocation;
	int targetOffset;

	SourceMapEntry(this.sourceLocation, this.targetOffset);
	}

	/// Map from line/column pairs to lists of [T] elements.
	class LineColumnMap<T> {
	final Map<int, Map<int, List<T>>> _map = {};

	/// Returns the list of elements associated with ([line],[column]).
	List<T> _getList(int line, int column) {
	Map<int, List<T>> lineMap = _map[line] ??= {};
	return lineMap[column] ??= [];
	}

	/// Adds [element] to the end of the list of elements associated with
	/// ([line],[column]).
	void add(int line, int column, T element) {
	_getList(line, column).add(element);
	}

	/// Adds [element] to the beginning of the list of elements associated with
	/// ([line],[column]).
	void addFirst(int line, int column, T element) {
	_getList(line, column).insert(0, element);
	}

	/// Calls [f] with the line number for each line with associated elements.
	///
	/// [f] is called in increasing line order.
	void forEachLine(f(int line)) {
	List<int> lines = _map.keys.toList()..sort();
	lines.forEach(f);
	}

	/// Returns the elements for the first the column in [line] that has
	/// associated elements.
	List<T> getFirstElementsInLine(int line) {
	Map<int, List<T>> lineMap = _map[line];
	if (lineMap == null) return null;
	List<int> columns = lineMap.keys.toList()..sort();
	return lineMap[columns.first];
	}

	/// Calls [f] for each column with associated elements in [line].
	///
	/// [f] is called in increasing column order.
	void forEachColumn(int line, f(int column, List<T> elements)) {
	Map<int, List<T>> lineMap = _map[line];
	if (lineMap != null) {
	List<int> columns = lineMap.keys.toList()..sort();
	columns.forEach((int column) {
	f(column, lineMap[column]);
	});
	}
	}

	/// Calls [f] for each line/column/element triplet in the map.
	///
	/// [f] is called in increasing line, column, element order.
	void forEach(f(int line, int column, T element)) {
	List<int> lines = _map.keys.toList()..sort();
	for (int line in lines) {
	Map<int, List<T>> lineMap = _map[line];
	List<int> columns = lineMap.keys.toList()..sort();
	for (int column in columns) {
	lineMap[column].forEach((e) => f(line, column, e));
	}
	}
	}

	/// Calls [f] for each element associated in the map.
	///
	/// [f] is called in increasing line, column, element order.
	void forEachElement(f(T element)) {
	forEach((line, column, element) => f(element));
	}
	}

	/// Map from [T] elements to assigned indices.
	class IndexMap<T> {
	Map<T, int> map = {};

	/// Register [element] and returns its index.
	int register(T element) {
	return map.putIfAbsent(element, () => map.length);
	}

	/// Returns the index of [element].
	int operator [](T element) => map[element];

	/// Returns the indexed elements.
	Iterable<T> get elements => map.keys;
	}