Generic parameter does not accept a union of generics

[azjezz]

The new system for capturing generic constrains introduced in acc7ee2 breaks PSL build.

see: https://github.com/azjezz/psl/runs/3041183878?check_suite_focus=true

I couldn't make a smaller repro 🤔

[psalm-github-bot]

Hey @azjezz, can you reproduce the issue on https://psalm.dev ?

[weirdan]

Simplified to https://psalm.dev/r/86a60c6f13

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/86a60c6f13

<?php

/**
 * @template T
 * @param Container<T> $_p
 */
function acceptsContainer($_p): void {
}

/** @param Container<int>|Container<string> $var */
function ff($var): void {
	acceptsContainer($var);
}

/**
 * @template T
 */
interface Container {}

/**
 * @template T
 * @param T $_p
 * @return Container<T>
 * @psalm-suppress InvalidReturnType
 */
function makeContainer($_p): Container {}

Psalm output (using commit 82dfbbc):

ERROR: InvalidArgument - 12:2 - Incompatible types found for T

[weirdan]

@muglug any idea what could be wrong here? It looks like Psalm breaks union apart into constituent types and believes each of them is an upper (?) bound for T:acceptsContainer and that doesn't sound right.

[muglug]

Yeah, have a look at this: https://psalm.dev/r/bbef3b2bdb

If there's one type for T then Psalm allows Container<int>|Container<string> to become Container<int|string> which is a violation of generic stuff.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/bbef3b2bdb

<?php

/**
 * @template T
 * @param Container<T> $p
 * @return Container<T>
 */
function acceptsContainer($p): Container {
    return $p;
}

/**
 * @param Container<int>|Container<string> $var
 * @return Container<int|string>
 */
function ff($var): Container {
	return acceptsContainer($var);
}

/**
 * @template T
 */
interface Container {}

/**
 * @template T
 * @param T $_p
 * @return Container<T>
 * @psalm-suppress InvalidReturnType
 */
function makeContainer($_p): Container {}

Psalm output (using commit 82dfbbc):

ERROR: InvalidArgument - 17:9 - Incompatible types found for T

[muglug]

PHPStan emits a slightly different but comparable error: https://phpstan.org/r/b1097877-6b2c-4f5b-b897-30a0b069bad4