UnusedVariable false positive with thrown and caught exceptions

[Daeroni]

If a variable is modified just before an exception is thrown, and then caught in the same context and the variable used, psalm emits an UnusedVariable issue.

https://psalm.dev/r/95027a9b22
https://3v4l.org/9UkSq

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/95027a9b22

<?php

function test(bool $b): string {
	$test = 'test';

	try {
    	if ($b) {
        	$test .= ' true';
        	throw new Exception;
    	}
	} catch (Exception $e) {
	}

    return $test . "\n";
}

print test(false);
print test(true);

Psalm output (using commit eb71506):

INFO: UnusedVariable - 8:10 - $test is never referenced or the value is not used

[muglug]

Also a different false-positive for type assignment (because unused variable tracking uses the same pathways): https://psalm.dev/r/621191710b

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/621191710b

<?php

function test(): void {
	$did_throw = false;

	try {
    	if (rand(0, 1)) {
        	$did_throw = true;
        	throw new Exception;
    	}
	} catch (Exception $e) {
	}
    
    if ($did_throw) {}
}

Psalm output (using commit eb71506):

ERROR: TypeDoesNotContainType - 14:9 - if (false) is impossible

INFO: UnusedVariable - 8:10 - $did_throw is never referenced or the value is not used

[tostiheld]

I also ran in this issue, and the issue went away after I downgraded all the way to 4.6.4