vimeo/psalm

str_replace with a polymorphic subject returns string

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#7,625 opened on Feb 10, 2022

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Description

The return type of str_replace is deduced to be string when I pass it a $subject (the third parameter) of type string | array<string>. A $subject of type string leads to the string return type, while array<float | int | string> leads to array<string>, which is correct. It only incorrectly assumes string when the $subject is of a union type.

https://psalm.dev/r/48f8c3f020

Contributor guide

Research direction
Investigate the type deduction logic for str replace in Psalm's type system, specifically handling of union types for the subject parameter.
Tech stack
php
Domain
tooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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
PHP
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65