vimeo/psalm

Psalm infers float|int when using template for positive-int|0

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#7,235 opened on Dec 28, 2021

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Description

Given the following snippet https://psalm.dev/r/28b89bee3b

<?php

/**
 * @psalm-pure
 * @psalm-template T as positive-int|0
 * @psalm-param T $depth
 */
function recursiveFn(int $depth = 1): void {
    if ($depth > 1) {
        recursiveFn($depth - 1);
    }
}

Psalm reports:

ERROR: ArgumentTypeCoercion - 10:21 - Argument 1 of recursiveFn expects 0|positive-int, parent type float|int provided

Given the exactly the same snippet, except not using the template https://psalm.dev/r/412e21cd88

<?php

/**
 * @psalm-pure
 * @psalm-param positive-int|0 $depth
 */
function recursiveFn(int $depth = 1): void {
    if ($depth > 1) {
        recursiveFn($depth - 1);
    }
}

There are no (related) errors; presumably $depth is correctly identified as positive-int|0 here.

Contributor guide

Research direction
Investigate how Psalm handles template type narrowing and compare with non template version. Focus on the type resolution of $depth after subtraction in the template case.
Tech stack
php
Domain
developer experience
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
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40