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Detect more possibly-impossible offset #4164

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Detect more possibly-impossible offset #4164

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VincentLanglet
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I feel like the error could always be reported on level 7+.

The difference is that the reportPossiblyUndefined... option is for offsets like string, but in this case this is about a union and one of the union parts never exists on the constant array so it'd be a good fit for L7+ without any extra option.

@VincentLanglet VincentLanglet changed the title Add non regression test Detect more possibly-impossible offset Jul 26, 2025
@VincentLanglet VincentLanglet marked this pull request as draft July 26, 2025 15:47
@VincentLanglet VincentLanglet force-pushed the test/1061 branch 10 times, most recently from c290ea1 to 2417411 Compare August 1, 2025 11:28
@VincentLanglet VincentLanglet marked this pull request as ready for review August 1, 2025 11:43
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ondrejmirtes
ondrejmirtes requested changes Aug 5, 2025
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tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php
@@ -127,6 +131,10 @@ public function testRule(): void
'Offset int does not exist on array<string, string>.',
312,
],
[
'Offset int|null might not exist on array<string, string>.',
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Well this is totally wrong, null gets cast to '' in an array key and that can exist on array<string, string>.. Not sure where to do the fix.

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You misunderstood the error message.

You can see that phpstan already report on line 312 (the error above)

'Offset int does not exist on array<string, string>.',

So here we're reporting the same message with "might not exist" certainty because

  • int does not exists
  • null can exist

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Fails to detect possibly-impossible constant offset
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@VincentLanglet @ondrejmirtes @phpstan-bot