Add duplicate parameter detection to preparser.

test/preparser/duplicate-parameter.pyt

+# Copyright 2011 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:
+#
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+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# Templatated tests with duplicate parameter names.
+
+# ----------------------------------------------------------------------
+# Constants and utility functions
+
+# A template that performs the same strict-mode test in different
+# scopes (global scope, function scope, and nested function scope),
+# and in non-strict mode too.
+def DuplicateParameterTest(name, source):
+  expectation = "strict_param_dupe"
+  non_selfstrict = {"selfstrict":"", "id":"selfnormal"}
+
+  Template(name, '"use strict";\n' + source)(non_selfstrict, expectation)
+  Template(name + '-infunc',
+      'function foo() {\n "use strict";\n' + source +'\n}\n')(
+      non_selfstrict, expectation)
+  Template(name + '-infunc2',
+      'function foo() {\n "use strict";\n  function bar() {\n' +
+      source +'\n }\n}\n')(non_selfstrict, expectation)
+
+  selfstrict = {"selfstrict": "\"use strict\";", "id": "selfstrict"}
+  nestedstrict = {"selfstrict": "function bar(){\"use strict\";}",
+                  "id": "nestedstrict"}
+  selfstrictnestedclean = {"selfstrict": """
+       "use strict";
+       function bar(){}
+     """, "id": "selfstrictnestedclean"}
+  selftest = Template(name + '-$id', source)
+  selftest(selfstrict, expectation)
+  selftest(selfstrictnestedclean, expectation)
+  selftest(nestedstrict, None)
+  selftest(non_selfstrict, None)
+
+
+# ----------------------------------------------------------------------
+# Test templates
+
+DuplicateParameterTest("dups", """
+  function foo(a, a) { $selfstrict }
+""");
+
+DuplicateParameterTest("dups-apart", """
+  function foo(a, b, c, d, e, f, g, h, i, j, k, l, m, n, a) { $selfstrict }
+""");
+
+DuplicateParameterTest("dups-escaped", """
+  function foo(\u0061, b, c, d, e, f, g, h, i, j, k, l, m, n, a) { $selfstrict }
+""");
+
+DuplicateParameterTest("triples", """
+  function foo(a, b, c, d, e, f, g, h, a, i, j, k, l, m, n, a) { $selfstrict }
+""");
+