Do not create conditional expressions of unrelated variables

Author: ondrejmirtes

src/Analyser/NodeScopeResolver.php

@@ -2977,6 +2977,7 @@ private function processAssignVar(
 			$result = $processExprCallback($scope);
 			$hasYield = $result->hasYield();
 			$throwPoints = $result->getThrowPoints();
+			$assignedExpr = $this->unwrapAssign($assignedExpr);
 			$type = $scope->getType($assignedExpr);
 			$truthySpecifiedTypes = $this->typeSpecifier->specifyTypesInCondition($scope, $assignedExpr, TypeSpecifierContext::createTruthy());
 			$falseySpecifiedTypes = $this->typeSpecifier->specifyTypesInCondition($scope, $assignedExpr, TypeSpecifierContext::createFalsey());
@@ -3167,6 +3168,15 @@ private function processAssignVar(
 		return new ExpressionResult($scope, $hasYield, $throwPoints);
 	}
 
+	private function unwrapAssign(Expr $expr): Expr
+	{
+		if ($expr instanceof Assign) {
+			return $this->unwrapAssign($expr->expr);
+		}
+
+		return $expr;
+	}
+
 	/**
 	 * @param Scope $scope
 	 * @param string $variableName

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -10338,6 +10338,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-4287.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-4700.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/phpdoc-in-closure-bind.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/multi-assign.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/multi-assign.php

@@ -0,0 +1,83 @@
+<?php
+
+namespace MultiAssign;
+
+use function PHPStan\Analyser\assertType;
+
+function (): void {
+	$foo = $bar = $baz = null;
+	assertType('null', $foo);
+	assertType('null', $bar);
+	assertType('null', $baz);
+	if (!$foo) {
+		assertType('null', $foo);
+		assertType('null', $bar);
+		assertType('null', $baz);
+	}
+
+	if (!$bar) {
+		assertType('null', $foo);
+		assertType('null', $bar);
+		assertType('null', $baz);
+	}
+};
+
+function (bool $b): void {
+	$foo = $bar = $baz = $b;
+	if ($b) {
+		assertType('true', $b);
+		assertType('bool', $foo);
+		assertType('bool', $bar);
+		assertType('bool', $baz);
+	} else {
+		assertType('false', $b);
+		assertType('bool', $foo);
+		assertType('bool', $bar);
+		assertType('bool', $baz);
+	}
+};
+
+function (bool $b): void {
+	$foo = $bar = $baz = $b;
+	if ($foo) {
+		assertType('true', $b);
+		assertType('true', $foo);
+		assertType('bool', $bar);
+		assertType('bool', $baz);
+	} else {
+		assertType('false', $b);
+		assertType('false', $foo);
+		assertType('bool', $bar);
+		assertType('bool', $baz);
+	}
+};
+
+function (bool $b): void {
+	$foo = $bar = $baz = $b;
+	if ($bar) {
+		assertType('bool', $b);
+		assertType('bool', $foo);
+		assertType('true', $bar);
+		assertType('bool', $baz);
+	} else {
+		assertType('bool', $b);
+		assertType('bool', $foo);
+		assertType('false', $bar);
+		assertType('bool', $baz);
+	}
+};
+
+function (bool $b): void {
+	$foo = $bar = $baz = $b;
+	if ($baz) {
+		assertType('bool', $b);
+		assertType('bool', $foo);
+		assertType('bool', $bar);
+		assertType('true', $baz);
+	} else {
+		assertType('bool', $b);
+		assertType('bool', $foo);
+		assertType('bool', $bar);
+		assertType('false', $baz);
+	}
+};