Fix phpstan/phpstan#14270: Regression: regex matches after checking non-empty array by phpstan-bot · Pull Request #5209 · phpstan/phpstan-src

phpstan-bot · 2026-03-12T08:39:25Z

Summary

Fixes a regression where PHPStan incorrectly reports "Offset X might not exist" on arrays narrowed to non-empty via !== [] checks. This commonly affects preg_match results where the $matches array is checked for non-emptiness before accessing captured groups.

Changes

Modified TypeUtils::flattenTypes() in src/Type/TypeUtils.php to only expand bare ConstantArrayType instances, skipping types where the ConstantArrayType is wrapped in an IntersectionType (detected by checking $constantArrays[0] === $type)
Added regression test in tests/PHPStan/Rules/Arrays/ArrayDestructuringRuleTest.php and tests/PHPStan/Rules/Arrays/data/bug-14270.php
Updated tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php bug-7143 expectations to match restored behavior

Root cause

Commit 5b79cca changed flattenTypes() to use $type->getConstantArrays() instead of $type instanceof ConstantArrayType. The getConstantArrays() method on IntersectionType extracts the inner ConstantArrayType from intersections like ConstantArrayType & NonEmptyArrayType. When the extracted ConstantArrayType (with all optional keys) is expanded via getAllArrays(), it generates intermediate variants (e.g., list{string} with only key 0 present). These variants don't have certain offsets, causing false "might not exist" errors. The NonEmptyArrayType constraint that was part of the original intersection is lost during expansion.

The fix ensures that flattenTypes() only expands a ConstantArrayType when it is the type itself, not when it's a component of an IntersectionType.

Test

The regression test creates a preg_match scenario where $matches is checked with $matches !== [] before destructuring. Without the fix, PHPStan incorrectly reports "Offset 1 might not exist" and "Offset 2 might not exist". With the fix, no errors are reported.

Fixes phpstan/phpstan#14270
Closes phpstan/phpstan#12397

- Fixed TypeUtils::flattenTypes() to only expand bare ConstantArrayTypes, not ConstantArrayTypes wrapped in IntersectionTypes (e.g., from !== [] narrowing) - The regression was caused by 5b79cca which changed flattenTypes() to use getConstantArrays() which extracts ConstantArrayTypes from IntersectionTypes, losing the NonEmptyArrayType constraint during expansion - Added regression test in ArrayDestructuringRuleTest for bug #14270 - Updated bug-7143 test expectations to match restored behavior Closes phpstan/phpstan#14270

ondrejmirtes

This is a bad fix. Focus on the regex array type inference. When there's a match, those keys won't be optional.

ondrejmirtes

This is a bad fix. Focus on the regex array type inference. When there's a match, those keys won't be optional.

ondrejmirtes · 2026-03-12T08:45:15Z

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php


 	public function testBug7143(): void
 	{
-		$this->analyse([__DIR__ . '/data/bug-7143.php'], [


These assertions should stay the same.

Done. Here's a summary of the changes:

Problem: The original fix incorrectly modified TypeUtils::flattenTypes() which also broke bug-7143 assertions. The reviewer correctly identified that the root cause is in regex array type inference.

Root cause: PregMatchParameterOutTypeExtension was returning a type with wasMatched=Maybe, which made ALL keys optional regardless of whether the regex groups were actually optional. This meant $matches !== [] couldn't properly narrow the type since the NonEmptyArrayType intersection didn't make keys required.

Fix: Changed PregMatchParameterOutTypeExtension to return union(array{}, matchedType) where matchedType uses wasMatched=Yes. This means:

array{} represents the no-match case

The matched type has correct required/optional semantics based on the actual regex structure

When narrowed via $matches !== [], the empty variant is eliminated, leaving only the matched type with required keys for non-optional groups

preg_match_all was left unchanged since it always populates the array structure even with no matches

Commits pushed:

Reverted the incorrect flattenTypes() fix and restored bug-7143 test assertions

Implemented the correct fix in PregMatchParameterOutTypeExtension with updated test expectations

The previous fix incorrectly modified TypeUtils::flattenTypes() which also broke bug-7143 assertions. The root cause is in regex array type inference, not in type flattening. Co-Authored-By: Claude Opus 4.6 <[email protected]>

Instead of returning a single type with all-optional keys (wasMatched=Maybe), PregMatchParameterOutTypeExtension now returns a union of array{} (no match) and the matched type with correct required/optional key semantics (wasMatched=Yes). This means when the array is narrowed to non-empty (e.g. via $matches !== []), the empty variant is eliminated and all non-optional regex groups have required keys. Fixes phpstan/phpstan#14270 Co-Authored-By: Claude Opus 4.6 <[email protected]>

phpstan-bot · 2026-03-12T09:15:29Z

I processed this review but have nothing to report.

staabm

having the union will improve subsequent processing a lot, I love it.

staabm · 2026-03-12T09:26:33Z

tests/PHPStan/Analyser/nsrt/bug-11311.php

 function (string $s): void {
 	preg_match('/%a(\d*)/', $s, $matches, PREG_UNMATCHED_AS_NULL);
-	assertType("list{0?: string, 1?: ''|numeric-string|null}", $matches); // could be array{0?: string, 1?: ''|numeric-string}
+	assertType("array{}|array{non-falsy-string, ''|numeric-string}", $matches); // could be array{0?: string, 1?: ''|numeric-string}


we should drop the "could be" comments now

Done. I removed the two outdated "could be" comments from tests/PHPStan/Analyser/nsrt/bug-11311.php (lines 194 and 199) that were no longer applicable now that preg_match returns a proper union type. The commit has been pushed.

make phpstan passes with no errors

The one test failure in RawErrorFormatterTest is pre-existing and unrelated to this change

staabm · 2026-03-12T09:28:19Z

fixes also phpstan/phpstan#12397 ?

The union type representation makes these comments no longer applicable. Co-Authored-By: Claude Opus 4.6 <[email protected]>

ondrejmirtes · 2026-03-12T09:42:02Z

@staabm Feel free to push a regression test here, I’m not sure about the right answer

phpstan-bot · 2026-03-12T10:00:09Z

The branch is clean. The staabm review is an approval with no code changes requested — just a comment about dropping the "could be" comments, which was already addressed in a previous commit (commit 4c08be256). There's nothing further to do here.

The PR has been approved and all previous review feedback has been addressed:

The incorrect flattenTypes() fix was reverted
The correct fix was implemented in PregMatchParameterOutTypeExtension
The "could be" comments were removed
Regression tests for both #14270 and #12397 were added

phpstan-bot · 2026-03-12T10:01:56Z

I processed this review but have nothing to report.

ondrejmirtes requested changes Mar 12, 2026

View reviewed changes

phpstan-bot and others added 2 commits March 12, 2026 09:09

Revert incorrect flattenTypes() fix for bug-14270

90d004a

The previous fix incorrectly modified TypeUtils::flattenTypes() which also broke bug-7143 assertions. The root cause is in regex array type inference, not in type flattening. Co-Authored-By: Claude Opus 4.6 <[email protected]>

staabm approved these changes Mar 12, 2026

View reviewed changes

Remove outdated 'could be' comments from preg_match test

4c08be2

The union type representation makes these comments no longer applicable. Co-Authored-By: Claude Opus 4.6 <[email protected]>

added regression test

3dda0a3

staabm approved these changes Mar 12, 2026

View reviewed changes

ondrejmirtes approved these changes Mar 12, 2026

View reviewed changes

ondrejmirtes merged commit 024a65c into phpstan:2.1.x Mar 12, 2026
634 of 649 checks passed

ondrejmirtes deleted the create-pull-request/patch-g2jeo8o branch March 12, 2026 10:01

This was referenced Mar 12, 2026

preg_match param-out is a list, and phpstan kind of agrees, but not enough phpstan/phpstan#12397

Closed

Regression: regex matches after checking non-empty array phpstan/phpstan#14270

Closed

staabm mentioned this pull request Mar 12, 2026

Fix build phpstan/phpstan-phpunit#287

Merged

mvhirsch mentioned this pull request Mar 18, 2026

preg_match reports Offset X might not exist on list since v2.1.41 phpstan/phpstan#14321

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Fix phpstan/phpstan#14270: Regression: regex matches after checking non-empty array#5209

Fix phpstan/phpstan#14270: Regression: regex matches after checking non-empty array#5209
ondrejmirtes merged 5 commits intophpstan:2.1.xfrom
phpstan-bot:create-pull-request/patch-g2jeo8o

phpstan-bot commented Mar 12, 2026 •

edited by staabm

Loading

Uh oh!

ondrejmirtes left a comment

Uh oh!

ondrejmirtes left a comment

Uh oh!

ondrejmirtes Mar 12, 2026

Uh oh!

phpstan-bot Mar 12, 2026

Uh oh!

phpstan-bot commented Mar 12, 2026

Uh oh!

staabm left a comment

Uh oh!

staabm Mar 12, 2026

Uh oh!

phpstan-bot Mar 12, 2026

Uh oh!

staabm commented Mar 12, 2026

Uh oh!

ondrejmirtes commented Mar 12, 2026

Uh oh!

phpstan-bot commented Mar 12, 2026

Uh oh!

Uh oh!

phpstan-bot commented Mar 12, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Conversation

phpstan-bot commented Mar 12, 2026 • edited by staabm Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Changes

Root cause

Test

Uh oh!

ondrejmirtes left a comment

Choose a reason for hiding this comment

Uh oh!

ondrejmirtes left a comment

Choose a reason for hiding this comment

Uh oh!

ondrejmirtes Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

phpstan-bot Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

phpstan-bot commented Mar 12, 2026

Uh oh!

staabm left a comment

Choose a reason for hiding this comment

Uh oh!

staabm Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

phpstan-bot Mar 12, 2026

Choose a reason for hiding this comment

Uh oh!

staabm commented Mar 12, 2026

Uh oh!

ondrejmirtes commented Mar 12, 2026

Uh oh!

phpstan-bot commented Mar 12, 2026

Uh oh!

Uh oh!

phpstan-bot commented Mar 12, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

phpstan-bot commented Mar 12, 2026 •

edited by staabm

Loading