@psalm-pure, : void methods (assertions) and exceptions

[Ocramius]

Further follow-up from work being done to improve webmozart/assert @ webmozarts/assert#160 (comment)

@psalm-pure doesn't seem to play well with :void expressions. There are a few things weird about the following code (https://psalm.dev/r/e34695a167):

<?php

/** @psalm-pure */
function stopOn1(int $v):void
{
  if ($v === 1) {
    throw new \RuntimeException();
  }
}

stopOn1(1);
stopOn1(2);
stopOn1(3);

Psalm output (using commit af52590):

ERROR: UnusedFunctionCall - 11:1 - The call to stopon1 is not used

ERROR: UnusedFunctionCall - 12:1 - The call to stopon1 is not used

ERROR: UnusedFunctionCall - 13:1 - The call to stopon1 is not used

Specifically:

• the new \RuntimeException() constructor is not @psalm-pure: I think this was discussed before with @weirdan (InvalidArgumentException constructor considered impure #2160)
• the function return value is expected to be used, but this function's only purpose is to throw

I think this is connected with #2160 (comment): thrown values are not considered function output.

Few possible resolutions:

• ignore UnusedFunctionCall if that result is void
• consider exceptions as return signature in all callers (this sounds like a mess, as it changes basic assumptions about the type system)

[muglug]

What if we ignore UnusedFunctionCall when the function has @psalm-assert?

[weirdan]

To me, :void indicates the return value should not be used, so why should Psalm complain about unused return? Or am I misunderstanding the nature of UnusedFunctionCall?

[weirdan]

Oh, I think I get it now: pure functions should return values that are used, otherwise calls to them are deemed useless.

[Ocramius]

What if we ignore UnusedFunctionCall when the function has @psalm-assert?

Seems reasonable.

[Ocramius]

Thanks @muglug! 🎉