src/v8/test/mjsunit/regexp-lookahead.js

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// Tests captures in positive and negative look-ahead in regular expressions.

function stringEscape(string) {
  // Converts string to source literal.
  return '"' + string.replace(/["\\]/g, "\\$1") + '"';
}

function testRE(re, input, expected_result) {
  var testName = re + ".test(" + stringEscape(input) +")";
  if (expected_result) {
    assertTrue(re.test(input), testName);
  } else {
    assertFalse(re.test(input), testName);
  }
}

function execRE(re, input, expected_result) {
  var testName = re + ".exec('" + stringEscape(input) +"')";
  assertEquals(expected_result, re.exec(input), testName);
}

// Test of simple positive lookahead.

var re = /^(?=a)/;
testRE(re, "a", true);
testRE(re, "b", false);
execRE(re, "a", [""]);

re = /^(?=\woo)f\w/;
testRE(re, "foo", true);
testRE(re, "boo", false);
testRE(re, "fao", false);
testRE(re, "foa", false);
execRE(re, "foo", ["fo"]);

re = /(?=\w).(?=\W)/;
testRE(re, ".a! ", true);
testRE(re, ".! ", false);
testRE(re, ".ab! ", true);
execRE(re, ".ab! ", ["b"]);

re = /(?=f(?=[^f]o))../;
testRE(re, ", foo!", true);
testRE(re, ", fo!", false);
testRE(re, ", ffo", false);
execRE(re, ", foo!", ["fo"]);

// Positive lookahead with captures.
re = /^[^\'\"]*(?=([\'\"])).*\1(\w+)\1/;
testRE(re, "  'foo' ", true);
testRE(re, '  "foo" ', true);
testRE(re, " \" 'foo' ", false);
testRE(re, " ' \"foo\" ", false);
testRE(re, "  'foo\" ", false);
testRE(re, "  \"foo' ", false);
execRE(re, "  'foo' ", ["  'foo'", "'", "foo"]);
execRE(re, '  "foo" ', ['  "foo"', '"', 'foo']);

// Captures are cleared on backtrack past the look-ahead.
re = /^(?:(?=(.))a|b)\1$/;
testRE(re, "aa", true);
testRE(re, "b", true);
testRE(re, "bb", false);
testRE(re, "a", false);
execRE(re, "aa", ["aa", "a"]);
execRE(re, "b", ["b", undefined]);

re = /^(?=(.)(?=(.)\1\2)\2\1)\1\2/;
testRE(re, "abab", true);
testRE(re, "ababxxxxxxxx", true);
testRE(re, "aba", false);
execRE(re, "abab", ["ab", "a", "b"]);

re = /^(?:(?=(.))a|b|c)$/;
testRE(re, "a", true);
testRE(re, "b", true);
testRE(re, "c", true);
testRE(re, "d", false);
execRE(re, "a", ["a", "a"]);
execRE(re, "b", ["b", undefined]);
execRE(re, "c", ["c", undefined]);

execRE(/^(?=(b))b/, "b", ["b", "b"]);
execRE(/^(?:(?=(b))|a)b/, "ab", ["ab", undefined]);
execRE(/^(?:(?=(b)(?:(?=(c))|d))|)bd/, "bd", ["bd", "b", undefined]);



// Test of Negative Look-Ahead.

re = /(?!x)./;
testRE(re, "y", true);
testRE(re, "x", false);
execRE(re, "y", ["y"]);

re = /(?!(\d))|\d/;
testRE(re, "4", true);
execRE(re, "4", ["4", undefined]);
execRE(re, "x", ["", undefined]);


// Test mixed nested look-ahead with captures.

re = /^(?=(x)(?=(y)))/;
testRE(re, "xy", true);
testRE(re, "xz", false);
execRE(re, "xy", ["", "x", "y"]);

re = /^(?!(x)(?!(y)))/;
testRE(re, "xy", true);
testRE(re, "xz", false);
execRE(re, "xy", ["", undefined, undefined]);

re = /^(?=(x)(?!(y)))/;
testRE(re, "xz", true);
testRE(re, "xy", false)
execRE(re, "xz", ["", "x", undefined]);

re = /^(?!(x)(?=(y)))/;
testRE(re, "xz", true);
testRE(re, "xy", false);
execRE(re, "xz", ["", undefined, undefined]);

re = /^(?=(x)(?!(y)(?=(z))))/;
testRE(re, "xaz", true);
testRE(re, "xya", true);
testRE(re, "xyz", false);
testRE(re, "a", false);
execRE(re, "xaz", ["", "x", undefined, undefined]);
execRE(re, "xya", ["", "x", undefined, undefined]);

re = /^(?!(x)(?=(y)(?!(z))))/;
testRE(re, "a", true);
testRE(re, "xa", true);
testRE(re, "xyz", true);
testRE(re, "xya", false);
execRE(re, "a", ["", undefined, undefined, undefined]);
execRE(re, "xa", ["", undefined, undefined, undefined]);
execRE(re, "xyz", ["", undefined, undefined, undefined]);