pkg/dev_compiler/lib/src/compiler/source_map_printer.dart

// Copyright (c) 2015, 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.

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/standard_resolution_map.dart';
import 'package:source_maps/source_maps.dart' hide Printer;
import 'package:source_span/source_span.dart' show SourceLocation;

import '../js_ast/js_ast.dart' as JS;

class SourceMapPrintingContext extends JS.SimpleJavaScriptPrintingContext {
  /// Current line in the buffer;
  int _line = 0;

  /// Current column in the buffer.
  int _column = 0;

  /// The source_maps builder we write JavaScript code to.
  final sourceMap = new SourceMapBuilder();

  CompilationUnit unit;
  String sourcePath;
  AstNode _currentTopLevelDeclaration;

  @override
  void emit(String code) {
    var chars = code.runes.toList();
    var length = chars.length;
    for (int i = 0; i < length; i++) {
      var c = chars[i];
      if (c == _LF || (c == _CR && (i + 1 == length || chars[i + 1] != _LF))) {
        // Return not followed by line-feed is treated as a new line.
        _line++;
        _column = 0;
      } else {
        _column++;
      }
    }
    super.emit(code);
  }

  void enterNode(JS.Node jsNode) {
    AstNode node = jsNode.sourceInformation;
    if (node == null || node.offset == -1) return;
    if (unit == null) {
      // This is a top-level declaration.  Note: consecutive top-level
      // declarations may come from different compilation units due to
      // parts.
      _currentTopLevelDeclaration = node;
      unit = node.getAncestor((n) => n is CompilationUnit);
      sourcePath =
          resolutionMap.elementDeclaredByCompilationUnit(unit).source.fullName;
    }

    _mark(node.offset, _getIdentifier(node));
  }

  void exitNode(JS.Node jsNode) {
    AstNode node = jsNode.sourceInformation;
    if (unit == null || node == null || node.offset == -1) return;

    // TODO(jmesserly): in many cases marking the end will be unnecessary.
    _mark(node.end);

    if (identical(node, _currentTopLevelDeclaration)) {
      unit = null;
      sourcePath = null;
      _currentTopLevelDeclaration == null;
    }
  }

  // TODO(jmesserly): prefix identifiers too, if they map to a named element.
  String _getIdentifier(AstNode node) =>
      node is SimpleIdentifier ? node.name : null;

  void _mark(int offset, [String identifier]) {
    var loc = unit.lineInfo.getLocation(offset);
    sourceMap.addLocation(
        new SourceLocation(offset,
            sourceUrl: sourcePath,
            line: loc.lineNumber - 1,
            column: loc.columnNumber - 1),
        new SourceLocation(buffer.length, line: _line, column: _column),
        identifier);
  }
}

const int _LF = 10;
const int _CR = 13;