Support multiple occurrences of text in context

lib/src/utils.dart

 // Copyright (c) 2014, 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 source_span.utils;
 
 /// Returns the minimum of [obj1] and [obj2] according to
 /// [Comparable.compareTo].
 Comparable min(Comparable obj1, Comparable obj2) =>
     obj1.compareTo(obj2) > 0 ? obj2 : obj1;
@@ skipping 19 matching lines @@
     var half = min + ((max - min) ~/ 2);
     if (matches(list[half])) {
       max = half;
     } else {
       min = half + 1;
     }
   }
   return max;
 }
 
+/// Finds a line in [context] containing [text] at the specified [column].
+///
+/// Returns the index in [context] where that line begins, or null if none
+/// exists.
+int findLineStart(String context, String text, int column) {
+  var isEmpty = text == '';
+  var index = context.indexOf(text);
+  while (index != -1) {
+    var lineStart = context.lastIndexOf('\n', index) + 1;
+    var textColumn = index - lineStart;
+    if (column == textColumn || (isEmpty && column == textColumn + 1)) {
+      return lineStart;
+    }
+    index = context.indexOf(text, index + 1);
+  }
+  return null;
+}