Implement lookbehind in regexp engine

tests/unsorted/lookbehind_test.dart

Index: tests/unsorted/lookbehind_test.dart
diff --git a/tests/unsorted/lookbehind_test.dart b/tests/unsorted/lookbehind_test.dart
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+// Copyright (c) 2015, the Dart project authors. All rights reserved.
+// Copyright 2009 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Some simple look-behind tests.
+
+import 'package:expect/expect.dart';
+
+// Utility functions to easily port V8 tests.
+
+void assertTrue(actual, [String message = null]) { Expect.isTrue(actual, message); }
+void assertFalse(actual, [String message = null]) { Expect.isFalse(actual, message); }
+
+void shouldBe(actual, expected, [String message = null]) {
+  if (expected == null) {
+    Expect.isNull(actual, message);
+  } else {
+    Expect.equals(expected.length, actual.groupCount + 1);
+    for (int i = 0; i <= actual.groupCount; i++) {
+      Expect.equals(expected[i], actual.group(i), message);
+    }
+  }
+}
+
+Match firstMatch(String str, RegExp pattern) => pattern.firstMatch(str);
+List<String> allStringMatches(String str, RegExp pattern) =>
+    pattern.allMatches(str).map((Match m) => m.group(0)).toList();
+
+void main() {
+  // Tests captures in positive and negative look-behind in regular expressions.
+
+  dynamic testRE(re, input, expected_result) {
+    if (expected_result) {
+      assertTrue(re.hasMatch(input));
+    } else {
+      assertFalse(re.hasMatch(input));
+    }
+  }
+
+  dynamic execRE(re, input, expected_result) {
+    shouldBe(re.firstMatch(input), expected_result);
+  }
+
+  // Test of simple positive lookbehind.
+
+  var re = new RegExp(r"^.(?<=a)");
+  testRE(re, "a", true);
+  testRE(re, "b", false);
+  execRE(re, "a", ["a"]);
+
+  re = new RegExp(r"^f..(?<=.oo)");
+  testRE(re, "foo1", true);
+
+  re = new RegExp(r"^f\w\w(?<=\woo)");
+  testRE(re, "foo2", true);
+  testRE(re, "boo", false);
+  testRE(re, "fao", false);
+  testRE(re, "foa", false);
+  execRE(re, "foo", ["foo"]);
+
+  // Positive lookbehind with captures.
+  re = new RegExp("(?<=(.))(\\w+)(?=\\1)");
+  testRE(re, "  'foo' ", true);
+  testRE(re, '  "foo" ', true);
+  testRE(re, '  .foo" ', false);
+  execRE(re, "  'foo' ", ["foo", "'", "foo"]);
+  execRE(re, '  "foo" ', ['foo', '"', 'foo']);
+
+  // Alternations are tried in left to right order and we don't backtrack into
+  // a lookbehind.
+  re = new RegExp(r".*(?<=(..|...|....))(.*)");
+  testRE(re, "xabcd", true);
+  execRE(re, "xabcd", ["xabcd", "cd", ""]);
+
+  re = new RegExp(r".*(?<=(xx|...|....))(.*)");
+  testRE(re, "xabcd", true);
+  execRE(re, "xabcd", ["xabcd", "bcd", ""]);
+
+  // Misc.
+  testRE(new RegExp("^foo(?<=foo)\$"), "foo", true);
+  testRE(new RegExp("^f.o(?<=foo)\$"), "foo", true);
+  testRE(new RegExp("^f.o(?<=foo)\$"), "fno", false);
+  
+  testRE(new RegExp("^foo(?<!foo)\$"), "foo", false);
+  testRE(new RegExp("^f.o(?<!foo)\$"), "foo", false);
+  testRE(new RegExp("^f.o(?<!foo)\$"), "fno", true);
+  
+  testRE(new RegExp("^foooo(?<=fo+)\$"), "foooo", true);
+  testRE(new RegExp("^foooo(?<=^fo+)\$"), "foooo", true);
+  testRE(new RegExp("^foooo(?<=^o+)\$"), "foooo", false);
+  testRE(new RegExp("^foooo(?<=fo*)\$"), "foooo", true);
+  testRE(new RegExp("^foooo(?<=^fo*)\$"), "foooo", true);
+  testRE(new RegExp("^foooo(?<=^o*)\$"), "foooo", false);
+  
+  testRE(new RegExp("^faaao?(?<=^f[oa]+(?=o))"), "faaao", true);
+  
+  re = new RegExp(r"(.)(?<=\1\1\1)");
+  testRE(re, "ab", false);
+  testRE(re, "abb", false);
+  testRE(re, "abbb", true);
+  re = new RegExp(r"(..)(?<=\1\1\1)");
+  testRE(re, "ab", false);
+  testRE(re, "abb", false);
+  testRE(re, "aabb", false);
+  testRE(re, "abab", false);
+  testRE(re, "fababab", true);
+  testRE(re, "fabxbab", false);
+  testRE(re, "faxabab", false);
+}