vimeo/psalm

preg_replace_callback with PREG_UNMATCHED_AS_NULL flag results in `null` elements in callback

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#7,671 opened on Feb 14, 2022

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Description

The stub for preg_replace_callback() is:

https://github.com/vimeo/psalm/blob/36d5a2a83c1d7b3e2aca1cfe9e9dcc916619e962/stubs/CoreGenericFunctions.phpstub#L922-L932

With @param callable(string[]):string $callback. However if you pass the PREG_UNMATCHED_AS_NULL flag the signature will become @param callable((string|null)[]):string $callback.

I have a $m[1] === null check in my callback function and now I get the errors:

ERROR: DocblockTypeContradiction - Cannot resolve types for $m[1] - docblock-defined type string does not contain null ERROR: RedundantConditionGivenDocblockType - Docblock-defined type string for $m[1] is never null

See https://psalm.dev/r/7537bf3352

https://3v4l.org/JdUaY shows the value of $m[1] is null.

Contributor guide

Research direction
Update the stub for preg replace callback in CoreGenericFunctions.phpstub to use a conditional return type that accounts for the PREG UNMATCHED AS NULL flag, making the callback parameter type (string|null)[] when the flag is passed.
Tech stack
php
Domain
None
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
PHPPsalm stubs
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65