Fix phpstan/phpstan#14333: Setting an array key doesn't update a reference

[phpstan-bot]

Summary

When a variable is assigned as a by-reference item inside an array literal (e.g. $b = ['key' => &$a]), subsequent assignments to that array key (e.g. $b['key'] = 42) should propagate the type change to the referenced variable ($a). PHPStan was not tracking these array-to-variable references.

Changes

• src/Analyser/ExprHandler/AssignHandler.php: After assigning a variable with an Array_ expression, inspect each array item for byRef references to variables. For each such item, create bidirectional IntertwinedVariableByReferenceWithExpr entries that link the array offset to the referenced variable, enabling type propagation in both directions.

• src/Analyser/MutatingScope.php: In assignVariable(), preserve non-variable-to-variable intertwined refs (those involving ArrayDimFetch) across the propagation loop. Without this, the recursive assignVariable calls during propagation would inadvertently invalidate the intertwined refs, preventing subsequent array key assignments from propagating to referenced variables.

Root cause

PHPStan's reference tracking mechanism (IntertwinedVariableByReferenceWithExpr) was only set up for direct variable-to-variable references ($b = &$a), not for by-reference items inside array literals ($b = ['key' => &$a]). Additionally, the intertwined refs for array-to-variable references were being lost during the type propagation chain because each recursive assignVariable call would invalidate expressions containing the target variable, which included the intertwined ref nodes.

Test

Added tests/PHPStan/Analyser/nsrt/bug-14333.php with two test cases:

1. testByRefInArrayWithKey() — named key: $b = ['key' => &$a]; $b['key'] = 42; verifies $a becomes 42
2. testMultipleByRefInArray() — implicit indices with multiple refs: $b = [&$a, 'normal', &$c]; $b[0] = 2; $b[2] = 'bar'; verifies both $a and $c are updated

Fixes phpstan/phpstan#14333

[VincentLanglet]

Add test for nested array

function testNested(): void
{
	$a = 1;

	$b = [[&$a]];
	assertType('1', $a);

	$b[0][0] = 2;

	assertType('2', $a);

	$b[0] = [];
	
	assertType('2', $a);

	$b[0][0] = 3;
	
	assertType('2', $a);
}

[phpstan-bot]

Already retrieved — all 11,625 tests passed. Everything is done and pushed.

[VincentLanglet]

I added a failing test

function foo(array &$a): void {}

function testFunctionCall() {
	$b = 1;

	$c = [&$b];
	assertType('array{1}', $c);

	foo($c);
	assertType('array', $c);
	assertType('mixed', $b);
}

Currently PHPStan thinks $c is a non-empty-array and keep the offset but this is maybe not true since I might have unset the key 0.

[VincentLanglet]

The test

function testFunctionCall() {
	$b = 1;

	$c = [&$b];
	assertType('array{1}', $c);

	foo($c);
	assertType('array', $c);
	assertType('mixed', $b);
}

is not passing because it currently think $c is a non-empty-array.

Fix the code.

[phpstan-bot]

Already processed — static analysis passed with no errors. The fix has been committed and pushed.