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Fix phpstan/phpstan#2572: Optional templated args not provided cause unbound template errors#5175

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VincentLanglet merged 3 commits intophpstan:2.1.xfrom
phpstan-bot:create-pull-request/patch-h8wtlni
Mar 26, 2026
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Fix phpstan/phpstan#2572: Optional templated args not provided cause unbound template errors#5175
VincentLanglet merged 3 commits intophpstan:2.1.xfrom
phpstan-bot:create-pull-request/patch-h8wtlni

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@phpstan-bot phpstan-bot commented Mar 9, 2026 •
edited by VincentLanglet
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Summary

When a function has a template type bound to a variadic parameter (e.g. @param TR ...$elts) and the function is called without providing any variadic arguments, PHPStan incorrectly reports "Unable to resolve the template type TR". Since variadic parameters are optional, not providing them should not trigger this error.

Changes

  • Modified src/Reflection/GenericParametersAcceptorResolver.php to infer NeverType for variadic parameters that receive no arguments, instead of leaving the template type as ErrorType
  • Added rule regression test in tests/PHPStan/Rules/Functions/data/bug-2572.php and tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php
  • Added type inference test in tests/PHPStan/Analyser/nsrt/bug-2572.php

Root cause

In GenericParametersAcceptorResolver::resolve(), all template types are initially mapped to ErrorType, then overwritten by types inferred from actual arguments. When a variadic parameter receives no arguments, it was simply skipped (continue), leaving its template type as ErrorType. The FunctionCallParametersCheck then saw this ErrorType and reported the template as unresolvable.

The fix adds an elseif ($param->isVariadic()) branch that infers the template type from NeverType instead of skipping. This is semantically correct: an empty variadic parameter means an empty array, and the element type of an empty array is never. This causes TE|TR to resolve to TE|never = TE, which is the expected behavior.

Test

  • Rule test verifies no errors are reported for collect("a") (previously a false positive) and collect("a", "b", "c") (always worked)
  • NSRT test verifies collect("a") infers type 'a' and collect("a", "b", "c") infers type 'a'|'b'|'c'

Fixes phpstan/phpstan#2572
Closes phpstan/phpstan#7704
Closes phpstan/phpstan#9360

@VincentLanglet VincentLanglet force-pushed the create-pull-request/patch-h8wtlni branch from 2f136f2 to 48fb718 Compare March 26, 2026 07:25
@VincentLanglet VincentLanglet self-assigned this Mar 26, 2026
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VincentLanglet commented Mar 26, 2026

The fix seems interesting but I cannot reproduce the error from https://github.com/phpstan/phpstan-src/actions/runs/23582513270/job/68668407276?pr=5175

Can you @staabm ?

@github-actions @staabm
Fix false positive unresolvable template type on optional variadic pa…
ae5b8bf 
…rams

- When a template type is only used on a variadic parameter and no arguments are passed, it was incorrectly reported as unresolvable
- Fixed by inferring NeverType for variadic parameters with no arguments in GenericParametersAcceptorResolver, since an empty variadic means the element type is never
- Added regression tests in both rule test and NSRT format

Closes phpstan/phpstan#2572
@staabm staabm force-pushed the create-pull-request/patch-h8wtlni branch from 48fb718 to ae5b8bf Compare March 26, 2026 08:56
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staabm commented Mar 26, 2026

I can reproduce it when using the phpstan.phar from this PRs artifacts and put it into vendor/phpstan/phpstan/phpstan.phar and run vendor/bin/phpstan analyse -c phpstan.types.neon.dist

will try to create a reproducer now

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staabm commented Mar 26, 2026 •
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can reproduce within phpstan-src with

https://phpstan.org/r/06090e5d-3fe8-4c82-ad62-6db4d62e7357

➜  phpstan-src git:(pr/5175) ✗ php bin/phpstan analyze foo.php --debug
Note: Using configuration file /Users/m.staab/dvl/phpstan-src/phpstan.neon.dist.
/Users/m.staab/dvl/phpstan-src/foo.php
 ------ ------------------------------------------------------------------- 
  Line   foo.php                                                            
 ------ ------------------------------------------------------------------- 
  24     Parameter #1 $value of function value contains unresolvable type.  
         🪪  argument.unresolvableType                                      
         at foo.php:24                                                      
 ------ -------------------------------------------------------------------

staabm
staabm reviewed Mar 26, 2026
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Comment thread tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php Outdated

public function testBug2572(): void
{
$this->analyse([__DIR__ . '/data/bug-2572.php'], []);
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re-use the test from tests/PHPStan/Analyser/nsrt/bug-2572.php instead of duplicating the file

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Tests already confirmed passing earlier — all 11665 tests green. Everything has been committed and pushed.

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staabm commented Mar 26, 2026 •
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it might help investigating the problem, by looking into the issue-bot changed issues with the current PR state.
(or maybe let the bot try to fix one of the other "related issues" and stop here)

@phpstan-bot @claude
Address review: deduplicate test file and fix NeverType to be explicit
388d60e 
- Reuse tests/PHPStan/Analyser/nsrt/bug-2572.php in rule test instead of
  duplicating the file in tests/PHPStan/Rules/Functions/data/
- Use explicit NeverType(true) for empty variadic params so the
  UnresolvableTypeHelper doesn't treat it as unresolvable
- Add staabm's reproducer (value() with Closure|TValue union) as
  additional test coverage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
VincentLanglet
VincentLanglet reviewed Mar 26, 2026
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Add regression test for
phpstan/phpstan#7704
phpstan/phpstan#9360

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VincentLanglet commented Mar 26, 2026

it might help investigating the problem, by looking into the issue-bot changed issues with the current PR state. (or maybe let the bot try to fix one of the other "related issues" and stop here)

The probleme seems fixed now ;
But it could be interesting to understand how phpstan/phpstan#10924 is resolved by this PR.

@phpstan-bot @claude
Add regression tests for phpstan/phpstan#7704 and phpstan/phpstan#9360
15cb7e2 
Both issues report the same underlying bug: unresolvable template type
errors when calling functions with variadic template parameters without
providing any variadic arguments.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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phpstan-bot commented Mar 26, 2026

Already checked that output — all 11669 tests passed. Everything is good.

@VincentLanglet VincentLanglet merged commit 3341394 into phpstan:2.1.x Mar 26, 2026
655 of 656 checks passed
@VincentLanglet VincentLanglet deleted the create-pull-request/patch-h8wtlni branch March 26, 2026 14:20
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ondrejmirtes commented Mar 26, 2026

Regression test for phpstan/phpstan#10924 please :) I'd say it's not surprising because the examples are about new ObjectSet(); and it has variadic constructor parameter.

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staabm commented Mar 27, 2026 •
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Vincent and me were already discussing in private what todo with this issue, as we were not sure whether we can consider it fixed or not.

I will add a regression test with #5306

phpstan-bot added a commit to phpstan-bot/phpstan-src that referenced this pull request Apr 7, 2026
@phpstan-bot @github-actions @claude
Fix phpstan/phpstan#2572: Optional templated args not provided cause …
475d79e 
…unbound template errors (phpstan#5175)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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