Implement modular compilation

lib/src/compiler/source_map_printer.dart

Index: lib/src/compiler/source_map_printer.dart
diff --git a/lib/src/compiler/source_map_printer.dart b/lib/src/compiler/source_map_printer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..dc289930e27b3c7a6847d7262402bafe3db51900
--- /dev/null
+++ b/lib/src/compiler/source_map_printer.dart
@@ -0,0 +1,89 @@
+// 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: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 = unit.element.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;