Narrow foreach body to non-empty regardless of polluteScopeWithAlwaysIterableForeach

[zonuexe]

Closes phpstan/phpstan#13312

/** @param list<mixed> $arr */
function foo(array $arr): void {
	foreach ($arr as $v) {
		bar($arr);
	}
}

/** @param non-empty-list<mixed> $arr */
function bar(array $arr): void {}

This reproduces with polluteScopeWithAlwaysIterableForeach: false, which phpstan-strict-rules sets.

Inside the loop body, $arr is provably non-empty. PHPStan already narrows it there, but only by accident: the narrowing came from polluteScopeWithAlwaysIterableForeach, a flag whose real job is to control what leaks into the scope after the loop, not what the loop body itself sees. With the flag off, the in-body narrowing disappeared along with it.

A previous fix (phpstan-src#4162) added a test for this narrowing, but only under the default polluteScopeWithAlwaysIterableForeach: true. Under phpstan-strict-rules, which sets it to false, the bug remained and the issue got reopened.

This PR narrows the iterated expression to non-empty at foreach-body entry unconditionally, so the flag now only affects the after-loop scope, as documented.

Note

DefinedVariableRuleTest::testBug8467c loses one of its two Variable $v might not be defined. expectations. $v is assigned in one foreach, then read inside a second, sibling foreach over an array only populated by the first loop's body — proving that second array non-empty also proves $v defined. Confirmed with \PHPStan\dumpType() that $v's type was always correctly int; the removed expectation was a false positive.