Add error description for nbsp character(\u202f) #178895

QuncCccccc · 2025-11-21T03:39:46Z

This PR is to add a more clear error description when there is a special white space NNBSP(\u202f). This whitespace character is used to connect time and "am"/"pm".

In this PR, I only updated the description in _MatchesSemanticsData and still not sure if it's necessary to create another custom matcher class to ignore special whitespace. I think it's valid to directly update users' test results since the expected results have indeed changed.

This is my experiment for the whitespace change when we update generated_date_localization.dart: cl/831625146
I went through all Scuba diffs and all results look expected. Once this is landed, we can use the CL change (except the image change) as g3fix to update the date localizations.

Fixes #177479

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I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
I read the [Tree Hygiene] wiki page, which explains my responsibilities.
I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
I signed the [CLA].
I listed at least one issue that this PR fixes in the description above.
I updated/added relevant documentation (doc comments with ///).
I added new tests to check the change I am making, or this PR is [test-exempt].
I followed the [breaking change policy] and added [Data Driven Fixes] where supported.
All existing and new tests are passing.

flutter-dashboard · 2025-11-21T03:39:49Z

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Code Review

This pull request aims to improve error messages for tests involving the narrow no-break space character (\u202f). The changes introduce helper methods to handle string comparisons and provide more specific feedback when a mismatch is due to this special whitespace. While the refactoring is a good idea, I've found a critical logical bug in the implementation that would cause test matchers to pass incorrectly. I've also identified a medium-severity issue regarding type safety and code clarity. I've provided suggestions to fix both issues.

packages/flutter_test/lib/src/matchers.dart

dkwingsmt · 2025-12-15T22:38:50Z

What is the result of this fix supposed to be? We should have a unit test to verify and demonstrate the result. And also I'm questioning the design, if I understand correctly.

QuncCccccc · 2025-12-18T18:59:40Z

What is the result of this fix supposed to be?

It is just to show a more clear error description in semantics check when nbsp('\u202f') is used in text. When we run date_localization script, a bunch of \u202f showing up but the error description only shows an empty space " " which is exactly the same as the normal empty space and it causes difficulty to debug. So we need to find a way to distinguish them.

Sorry I missed a unit test! Added one!

dkwingsmt · 2025-12-18T19:53:15Z

Note: I was skeptical of the design of the error messages, because I thought it would be better to show the original nbsp character in the expected string and instead explain the details with appended descriptions, such as "where the 5th character is \nbsp", so that the shown expected string itself is true and copiable.

I talked with Qun, and understands now that it is intentional that the expected string contains the escaped string, so that maintainers can simply copy the entire string to the source file.

The design looks good to me. I'll make a full review after the checks are green.

dkwingsmt · 2025-12-18T19:57:55Z

@QuncCccccc Another question: Will this change handle the case where the expected string uses spaces and the actual string uses nbsp?

QuncCccccc · 2025-12-18T20:21:50Z

Yes, in the unit test, we set the actual value to be "AAA\u202fBBB", and expected to be "AAA BBB", the error description shows the value should be "AAA\u202fBBB". If we reverse the actual and expected, like setting actual to be "AAA BBB", and set expected to be "AAA\u202fBBB", then the description will say the value should be "AAA BBB", and developers can still just copy and paste the message. Does that make sense? I can talk about it offline anytime:)!

chunhtai · 2025-12-18T21:44:11Z

packages/flutter_test/lib/src/matchers.dart

+      final String actualWithNBSP = actual.replaceAll('\u202f', r'\u202f');
+      return failWithDescription(matchState, '$prefixText was $actualWithNBSP');
+    }
+    return failWithDescription(matchState, '$prefixText was $actual');


why not also apply final String actualWithNBSP = actual.replaceAll('\u202f', r'\u202f'); here?

expect('another\u202fString' , 'some String');

will first show 'another String', and then developer copy over they will see 'another\u202fString' which is unecessary two step correction

Ah it makes sense! Updated!

chunhtai · 2025-12-18T21:46:51Z

packages/flutter_test/lib/src/matchers.dart

+    if (expected!.string != actual!.string) {
+      return _checkStringMismatch(matchState, prefixText, expected.string, actual.string);
+    }
+    return failWithDescription(matchState, '$prefixText was: $actual');


same should consider add final String actualWithNBSP = actual.replaceAll('\u202f', r'\u202f')
otherwise if the expect string are correctly using \u202f they error message will display string without the \u202f

Updated! Thanks!

dkwingsmt · 2025-12-18T21:54:48Z

Yes, in the unit test, we set the actual value to be "AAA\u202fBBB", and expected to be "AAA BBB", the error description shows the value should be "AAA\u202fBBB". If we reverse the actual and expected, like setting actual to be "AAA BBB", and set expected to be "AAA\u202fBBB", then the description will say the value should be "AAA BBB", and developers can still just copy and paste the message. Does that make sense? I can talk about it offline anytime:)!

Sounds good. Can you add a unit test for it?

QuncCccccc · 2025-12-18T23:05:29Z

Can you add a unit test for it?

Done.

chunhtai

LGTM

dkwingsmt · 2025-12-19T21:04:42Z

packages/flutter_test/lib/src/matchers.dart

+    final String actualStringWithNBSP = actual.string.replaceAll('\u202f', r'\u202f');
+    final actualWithNBSP = AttributedString(actualStringWithNBSP, attributes: actual.attributes);
+    return failWithDescription(matchState, '$prefixText was: $actualWithNBSP');


nit: Rename it with "escaped", a more common way to call this process

Suggested change

final String actualStringWithNBSP = actual.string.replaceAll('\u202f', r'\u202f');

final actualWithNBSP = AttributedString(actualStringWithNBSP, attributes: actual.attributes);

return failWithDescription(matchState, '$prefixText was: $actualWithNBSP');

final String actualStringEscaped = actual.string.replaceAll('\u202f', r'\u202f');

final actualEscaped = AttributedString(actualStringEscaped, attributes: actual.attributes);

return failWithDescription(matchState, '$prefixText was: $actualEscaped');

dkwingsmt · 2025-12-19T21:05:53Z

packages/flutter_test/lib/src/matchers.dart

+    final String actualWithNBSP = actual.replaceAll('\u202f', r'\u202f');
+    return failWithDescription(matchState, '$prefixText was $actualWithNBSP');


nit: Rename it with "escaped", a more common way to call this process

Suggested change

final String actualWithNBSP = actual.replaceAll('\u202f', r'\u202f');

return failWithDescription(matchState, '$prefixText was $actualWithNBSP');

final String actualEscaped = actual.replaceAll('\u202f', r'\u202f');

return failWithDescription(matchState, '$prefixText was $actualEscaped');

dkwingsmt · 2025-12-19T21:14:51Z

packages/flutter_test/test/matchers_test.dart

+            isA<TestFailure>().having(
+              (TestFailure e) => e.message,
+              'message',
+              contains(r'label was label 0'),


Will the error message in this case show a "space" in both expected and actual, since I think you only escaped one of them? In that case this PR is not solving this problem completely, but I'll leave it to you to decide whether it's acceptable.

I see! I think it makes sense. :) I updated the error description for both actual and expected, so it now contains 202f regardless of whether it's in actual or expected.

dkwingsmt

LGTM. Thank you for the cleanup!

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		final String actualWithNBSP = actual.replaceAll('\u202f', r'\u202f');
		return failWithDescription(matchState, '$prefixText was $actualWithNBSP');

Add error description for nbsp character(\u202f) #178895

Add error description for nbsp character(\u202f) #178895

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