When faced with a single number < 1000, Firefox rejects the format, which other engines allow with differing behavior:

The Chrome behavior is as follows:

• 0 is year 2000
• 1-12 are parsed as a month (and the year is defaulted to 2001)
• 13-31 are rejected
• 31-49 are years 2031-2049
• 50-99 are years 1950-1999
• 100-999 are years 100-999
• >= 1000 is a valid spec date and is parsed as such (works in all engines)

This is consistent with the dashed numeric date behavior when the year has < 4 digits. I personally think that the behavior for 1-31 is silly, and these should be seen as years if there is only a single number in the date string, however I don't wish to purposely create a third differing behavior between the browsers.

Backed out with Bug 1871220 for causing remote failures on browser_RemoteValue.js (date error)

• backout: https://hg.mozilla.org/integration/autoland/rev/0711306fada1fb772a273c24ba7916c779896cf3
• push: https://treeherder.mozilla.org/jobs?repo=autoland&group_state=expanded&selectedTaskRun=WYfpDjZRQoqD_ge05tfUWQ.0&revision=328ba82c361f4b9c538d46a8e2921552fc374e85
• failure log: https://treeherder.mozilla.org/logviewer?job_id=441119130&repo=autoland&lineNumber=54562

[task 2023-12-22T09:21:50.307Z] 09:21:50     INFO - TEST-PASS | remote/webdriver-bidi/test/browser/browser_RemoteValue.js | . Got expected error for date string: 10 - 
[task 2023-12-22T09:21:50.308Z] 09:21:50     INFO - Checking '20009'
[task 2023-12-22T09:21:50.309Z] 09:21:50     INFO - Buffered messages finished
[task 2023-12-22T09:21:50.316Z] 09:21:50     INFO - TEST-UNEXPECTED-FAIL | remote/webdriver-bidi/test/browser/browser_RemoteValue.js | Missing expected exception. Got expected error for date string: 20009 - {"filename":"chrome://mochitests/content/browser/remote/webdriver-bidi/test/browser/browser_RemoteValue.js","name":"test_deserializeDateLocalValueInvalidValues","sourceId":602,"lineNumber":624,"columnNumber":12,"sourceLine":"","asyncCause":null,"asyncCaller":null,"caller":{"filename":"chrome://mochikit/content/browser-test.js","name":"handleTask","sourceId":553,"lineNumber":1138,"columnNumber":26,"sourceLine":"","asyncCause":null,"asyncCaller":null,"caller":{"filename":"chrome://mochikit/content/browser-test.js","name":"_runTaskBasedTest","sourceId":553,"lineNumber":1210,"columnNumber":18,"sourceLine":"","asyncCause":null,"asyncCaller":{"filename":"chrome://mochikit/content/browser-test.js","name":"Tester_execTest","sourceId":553,"lineNumber":1352,"columnNumber":14,"sourceLine":"","asyncCause":null,"asyncCaller":null,"caller":{"filename":"chrome://mochikit/content/browser-test.js","name":"nextTest/<","sourceId":553,"lineNumber":1127,"columnNumber":14,"sourceLine":"","asyncCause":null,"asyncCaller":null,"caller":{"filename":"chrome://mochikit/content/tests/SimpleTest/SimpleTest.js","name":"SimpleTest.waitForFocus/<","sourceId":580,"lineNumber":1058,"columnNumber":13,"sourceLine":"","asyncCause":null,"asyncCaller":null,"caller":null,"formattedStack":"SimpleTest.waitForFocus/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:1058:13\n","nativeSavedFrame":{}},"formattedStack":"nextTest/<@chrome://mochikit/content/browser-test.js:1127:14\nSimpleTest.waitForFocus/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:1058:13\n","nativeSavedFrame":{}},"formattedStack":"async*Tester_execTest@chrome://mochikit/content/browser-test.js:1352:14\nnextTest/<@chrome://mochikit/content/browser-test.js:1127:14\nSimpleTest.waitForFocus/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:1058:13\n","nativeSavedFrame":{}},"caller":null,"formattedStack":"_runTaskBasedTest@chrome://mochikit/content/browser-test.js:1210:18\nasync*Tester_execTest@chrome://mochikit/content/browser-test.js:1352:14\nnextTest/<@chrome://mochikit/content/browser-test.js:1127:14\nSimpleTest.waitForFocus/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:1058:13\n","nativeSavedFrame":{}},"formattedStack":"handleTask@chrome://mochikit/content/browser-test.js:1138:26\n_runTaskBasedTest@chrome://mochikit/content/browser-test.js:1210:18\nasync*Tester_execTest@chrome://mochikit/content/browser-test.js:1352:14\nnextTest/<@chrome://mochikit/content/browser-test.js:1127:14\nSimpleTest.waitForFocus/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:1058:13\n","nativeSavedFrame":{}},"formattedStack":"test_deserializeDateLocalValueInvalidValues@chrome://mochitests/content/browser/remote/webdriver-bidi/test/browser/browser_RemoteValue.js:624:12\nhandleTask@chrome://mochikit/content/browser-test.js:1138:26\n_runTaskBasedTest@chrome://mochikit/content/browser-test.js:1210:18\nasync*Tester_execTest@chrome://mochikit/content/browser-test.js:1352:14\nnextTest/<@chrome://mochikit/content/browser-test.js:1127:14\nSimpleTest.waitForFocus/<@chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:1058:13\n","nativeSavedFrame":{}}
[task 2023-12-22T09:21:50.316Z] 09:21:50     INFO - Stack trace:
[task 2023-12-22T09:21:50.317Z] 09:21:50     INFO - chrome://mochitests/content/browser/remote/webdriver-bidi/test/browser/browser_RemoteValue.js:test_deserializeDateLocalValueInvalidValues:624
[task 2023-12-22T09:21:50.317Z] 09:21:50     INFO - chrome://mochikit/content/browser-test.js:handleTask:1138
[task 2023-12-22T09:21:50.317Z] 09:21:50     INFO - chrome://mochikit/content/browser-test.js:_runTaskBasedTest:1210
[task 2023-12-22T09:21:50.317Z] 09:21:50     INFO - chrome://mochikit/content/browser-test.js:Tester_execTest:1352
[task 2023-12-22T09:21:50.318Z] 09:21:50     INFO - chrome://mochikit/content/browser-test.js:nextTest/<:1127
[task 2023-12-22T09:21:50.318Z] 09:21:50     INFO - chrome://mochikit/content/tests/SimpleTest/SimpleTest.js:SimpleTest.waitForFocus/<:1058
[task 2023-12-22T09:21:50.319Z] 09:21:50     INFO - TEST-PASS | remote/webdriver-bidi/test/browser/browser_RemoteValue.js | . Got expected error for date string: 20009 - 

I believe this error SUMMARY: AddressSanitizer: heap-buffer-overflow /builds/worker/checkouts/gecko/js/src/jsdate.cpp:1908 in ParseDate was also caused by this patch.

Failure log: https://treeherder.mozilla.org/logviewer?job_id=441118042&repo=autoland&lineNumber=11888

https://hg.mozilla.org/mozilla-central/rev/9660032084db

• Content PR
• Firefox Release PR