Wrong resolving of generics inside try/catch block

[honzatrtik]

Code snippet that reproduces the problem

https://phpstan.org/r/ecf86117-177b-439c-b8e3-4e3040a8b6e2

Ends with
Function fromCallbackThatCanThrow() should return Option<T> but returns Option<*NEVER*>.

Additionally, if we set return values to variable as follows:

/**
 * @template T
 * @param callable():T $fn
 * @return Option<T>
 */
function fromCallbackThatCanThrow(callable $fn) {
	try {
		$a = some($fn());
	} catch (Throwable $failure) {
		$a = none();
	}
	return $a;
};

https://phpstan.org/r/dca44c7f-7e85-4f99-a66c-0b4629a25901

then the reported error is even more confusing:
Function fromCallbackThatCanThrow() should return Option<T> but returns Option<*NEVER*>|Option<T>.

If never is subtype of T (its universal subtype - bottom type, so it should be) and T is covariant, then Option<never> should be also subtype of Option<T>. So Option<never>| Option<T> should be Option<T>

Expected output

No errors should be reported

[ondrejmirtes]

I guess that never could be accepted as T.

[ZebulanStanphill]

Yeah, that's the case in TypeScript. T | never is equal to T.

[phpstan-bot]

@honzatrtik After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-PHP 8.0 – 8.1 (1 error)
+PHP 8.0 – 8.1
 ==========
 
-58: Function fromCallbackThatCanThrow() should return Option<T> but returns Option<*NEVER*>.
+No errors
 
-PHP 7.1 – 7.4 (2 errors)
+PHP 7.1 – 7.4 (1 error)
 ==========
 
-22: Promoted properties are supported only on PHP 8.0 and later.
-58: Function fromCallbackThatCanThrow() should return Option<T> but returns Option<*NEVER*>.
+22: Promoted properties are supported only on PHP 8.0 and later.

Full report

PHP 8.0 – 8.1

No errors

PHP 7.1 – 7.4 (1 error)

Line	Error
22	Promoted properties are supported only on PHP 8.0 and later.

[phpstan-bot]

@honzatrtik After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-PHP 8.0 – 8.1 (1 error)
+PHP 8.0 – 8.1
 ==========
 
-60: Function fromCallbackThatCanThrow() should return Option<T> but returns Option<*NEVER*>|Option<T>.
+No errors
 
-PHP 7.1 – 7.4 (2 errors)
+PHP 7.1 – 7.4 (1 error)
 ==========
 
-22: Promoted properties are supported only on PHP 8.0 and later.
-60: Function fromCallbackThatCanThrow() should return Option<T> but returns Option<*NEVER*>|Option<T>.
+22: Promoted properties are supported only on PHP 8.0 and later.

Full report

PHP 8.0 – 8.1

No errors

PHP 7.1 – 7.4 (1 error)

Line	Error
22	Promoted properties are supported only on PHP 8.0 and later.

[ondrejmirtes]

Fixed: phpstan/phpstan-src@c2b9e71

[github-actions]

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