Add some user-friendly utility functions to pkg/analyzer_experimental.

pkg/analyzer_experimental/lib/src/error.dart

Index: pkg/analyzer_experimental/lib/src/error.dart
diff --git a/pkg/analyzer_experimental/lib/src/error.dart b/pkg/analyzer_experimental/lib/src/error.dart
new file mode 100644
index 0000000000000000000000000000000000000000..668dedbf036d414c6a22b05527a33a57baac0cee
--- /dev/null
+++ b/pkg/analyzer_experimental/lib/src/error.dart
@@ -0,0 +1,104 @@
+// Copyright (c) 2013, 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 'dart:collection';
+import 'dart:io';
+import 'dart:math' as math;
+
+import 'generated/error.dart';
+import 'generated/java_core.dart';
+import 'generated/source.dart';
+
+/// The maximum line length when printing extracted source code when converting
+/// an [AnalyzerError] to a string.
+final _MAX_ERROR_LINE_LENGTH = 120;
+
+/// An error class that collects multiple [AnalyzerError]s that are emitted
+/// during a single analysis.
+class AnalyzerErrorGroup implements Exception {
+  /// The errors in this collection.
+  List<AnalyzerError> get errors =>
+    new UnmodifiableListView<AnalyzerError>(_errors);
+  final List<AnalyzerError> _errors;
+
+  AnalyzerErrorGroup(Iterable<AnalyzerError> errors)
+      : _errors = errors.toList();
+
+  /// Creates an [AnalyzerErrorGroup] from a list of lower-level
+  /// [AnalysisError]s.
+  AnalyzerErrorGroup.fromAnalysisErrors(Iterable<AnalysisError> errors)
+      : this(errors.map((e) => new AnalyzerError(e)));
+
+  String get message => toString();
+  String toString() => errors.join("\n");
+}
+
+/// A wrapper around [AnalysisError] that provides a more user-friendly string
+/// representation.
+class AnalyzerError implements Exception {
+  final AnalysisError error;
+
+  AnalyzerError(this.error);
+
+  String get message => toString();
+
+  String toString() {
+    var builder = new StringBuffer();
+    var receiver = new _ContentReceiver();
+    error.source.getContents(receiver);
+    var beforeError = receiver.result.substring(0, error.offset);
+    var lineNumber = "\n".allMatches(beforeError).length + 1;
+    builder.writeln("Error on line $lineNumber of ${error.source.fullName}: "
+        "${error.message}");
+
+    var errorLineIndex = beforeError.lastIndexOf("\n") + 1;
+    var errorEndOfLineIndex = receiver.result.indexOf("\n", error.offset);
+    if (errorEndOfLineIndex == -1) errorEndOfLineIndex = receiver.result.length;
+    var errorLine = receiver.result.substring(
+        errorLineIndex, errorEndOfLineIndex);
+    var errorColumn = error.offset - errorLineIndex;
+    var errorLength = error.length;
+
+    // Ensure that the error line we display isn't too long.
+    if (errorLine.length > _MAX_ERROR_LINE_LENGTH) {
+      var leftLength = errorColumn;
+      var rightLength = errorLine.length - leftLength;
+      if (leftLength > _MAX_ERROR_LINE_LENGTH ~/ 2 &&
+          rightLength > _MAX_ERROR_LINE_LENGTH ~/ 2) {
+        errorLine = "..." + errorLine.substring(
+            errorColumn - _MAX_ERROR_LINE_LENGTH ~/ 2 + 3,
+            errorColumn + _MAX_ERROR_LINE_LENGTH ~/ 2 - 3)
+            + "...";
+        errorColumn = _MAX_ERROR_LINE_LENGTH ~/ 2;
+      } else if (rightLength > _MAX_ERROR_LINE_LENGTH ~/ 2) {
+        errorLine = errorLine.substring(0, _MAX_ERROR_LINE_LENGTH - 3) + "...";
+      } else {
+        assert(leftLength > _MAX_ERROR_LINE_LENGTH ~/ 2);
+        errorColumn -= errorLine.length - _MAX_ERROR_LINE_LENGTH;
+        errorLine = "..." + errorLine.substring(
+            errorLine.length - _MAX_ERROR_LINE_LENGTH + 3, errorLine.length);
+      }
+      errorLength = math.min(errorLength, _MAX_ERROR_LINE_LENGTH - errorColumn);
+    }
+    builder.writeln(errorLine);
+
+    for (var i = 0; i < errorColumn; i++) builder.write(" ");
+    for (var i = 0; i < errorLength; i++) builder.write("^");
+    builder.writeln();
+
+    return builder.toString();
+  }
+}
+
+// A content receiver that collects all the content into a string.
+class _ContentReceiver implements Source_ContentReceiver {
+  final _buffer = new StringBuffer();
+
+  String get result => _buffer.toString();
+
+  void accept1(CharBuffer contents, _) =>
+    _buffer.write(contents.subSequence(0, contents.length));
+
+  void accept2(String contents, _) => _buffer.write(contents);
+}