Emit to StreamCodeOutput instead of CodeBuffer.

pkg/compiler/lib/src/io/line_column_provider.dart

+// 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.io.line_column;
+
+import 'code_output.dart';
+
+/// Interface for providing line/column information.
+abstract class LineColumnProvider {
+  /// Returns the line number (0-based) for [offset].
+  int getLine(int offset);
+
+  /// Returns the column number (0-based) for [offset] at the given [line].
+  int getColumn(int line, int offset);
+}
+
+/// [CodeOutputListener] that collects line information.
+class LineColumnCollector extends CodeOutputListener
+    implements LineColumnProvider {
+  int lastLineStart = 0;
+  List<int> lineStarts = <int>[0];
+
+  void _collect(String text) {
+    int offset = lastLineStart;
+    int index = 0;
+    while (index < text.length) {
+      // Unix uses '\n' and Windows uses '\r\n', so this algorithm works for
+      // both platforms.
+      index = text.indexOf('\n', index) + 1;
+      if (index <= 0) break;
+      lastLineStart = offset + index;
+      lineStarts.add(lastLineStart);
+    }
+  }
+
+  @override
+  void onText(String text) {
+    _collect(text);
+  }
+
+  @override
+  int getLine(int offset) {
+    List<int> starts = lineStarts;
+    if (offset < 0 || starts.last <= offset) {
+      throw 'bad position #$offset in buffer with length ${lineStarts.last}.';
+    }
+    int first = 0;
+    int count = starts.length;
+    while (count > 1) {
+      int step = count ~/ 2;
+      int middle = first + step;
+      int lineStart = starts[middle];
+      if (offset < lineStart) {
+        count = step;
+      } else {
+        first = middle;
+        count -= step;
+      }
+    }
+    return first;
+  }
+
+  @override
+  int getColumn(int line, int offset) {
+    return offset - lineStarts[line];
+  }
+
+  @override
+  void onDone(int length) {
+    lineStarts.add(length);
+  }
+}