Add optional start index to Pattern.allMatches.

tests/language/reg_exp_test.dart

 // Copyright (c) 2011, 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.
 // Dart test for testing regular expressions in Dart.
 
 import "package:expect/expect.dart";
 
 void main() {
   RegExp exp = new RegExp(r"(\w+)");
   String str = "Parse my string";
   List<Match> matches = exp.allMatches(str).toList();
   Expect.equals(3, matches.length);
   Expect.equals("Parse", matches[0].group(0));
   Expect.equals("my", matches[1].group(0));
   Expect.equals("string", matches[2].group(0));
 
   // Check that allMatches progresses correctly for empty matches, and that
   // it includes the empty match at the end position.
   exp = new RegExp("a?");
   str = "babba";
   Expect.listEquals(["", "a", "", "", "a", ""],
                     exp.allMatches(str).map((x)=>x[0]).toList());
 
+  // Check that allMatches works with optional start index.
+  exp = new RegExp("as{2}");
+  str = "assassin";
+  Expect.equals(2, exp.allMatches(str).length);
+  Expect.equals(2, exp.allMatches(str, 0).length);
+  Expect.equals(1, exp.allMatches(str, 1).length);
+  Expect.equals(0, exp.allMatches(str, 4).length);
+  Expect.equals(0, exp.allMatches(str, str.length).length);
+  Expect.throws(() => exp.allMatches(str, -1));
+  Expect.throws(() => exp.allMatches(str, str.length + 1));
+
+  exp = new RegExp(".*");
+  Expect.equals("", exp.allMatches(str, str.length).single[0]);
+
+  // The "^" must only match at the beginning of the string.
+  // Using a start-index doesn't change where the string starts.
+  exp = new RegExp("^ass");
+  Expect.equals(1, exp.allMatches(str, 0).length);
+  Expect.equals(0, exp.allMatches(str, 3).length);
+
   // Regression test for http://dartbug.com/2980
   exp = new RegExp("^", multiLine: true);  // Any zero-length match will work.
   str = "foo\nbar\nbaz";
   Expect.equals(" foo\n bar\n baz", str.replaceAll(exp, " "));
 
   exp = new RegExp(r"(\w+)");
   Expect.isNull(exp.matchAsPrefix(" xyz ab"));
   Expect.isNull(exp.matchAsPrefix(" xyz ab", 0));
 
   var m = exp.matchAsPrefix(" xyz ab", 1);
@@ skipping 21 matching lines @@
   m = exp.matchAsPrefix(" xyz ab", 6);
   Expect.equals("b", m[0]);
   Expect.equals("b", m[1]);
   Expect.equals(1, m.groupCount);
 
   Expect.isNull(exp.matchAsPrefix(" xyz ab", 7));
 
   Expect.throws(() => exp.matchAsPrefix(" xyz ab", -1));
   Expect.throws(() => exp.matchAsPrefix(" xyz ab", 8));
 }