Fix assigning arbitrary expressions in foreach key

src/Analyser/NodeScopeResolver.php

@@ -72,6 +72,7 @@
 use PHPStan\Node\ClosureReturnStatementsNode;
 use PHPStan\Node\DoWhileLoopConditionNode;
 use PHPStan\Node\ExecutionEndNode;
+use PHPStan\Node\Expr\GetIterableKeyTypeExpr;
 use PHPStan\Node\Expr\GetIterableValueTypeExpr;
 use PHPStan\Node\Expr\GetOffsetValueTypeExpr;
 use PHPStan\Node\Expr\OriginalPropertyTypeExpr;
@@ -3728,12 +3729,12 @@ private function enterForeach(MutatingScope $scope, Foreach_ $stmt): MutatingSco
 			$scope = $this->processVarAnnotation($scope, [$stmt->expr->name], $stmt);
 		}
 		$iterateeType = $scope->getType($stmt->expr);
-		if ($stmt->valueVar instanceof Variable && is_string($stmt->valueVar->name)) {
+		if (
+			($stmt->valueVar instanceof Variable && is_string($stmt->valueVar->name))
+			&& ($stmt->keyVar === null || ($stmt->keyVar instanceof Variable && is_string($stmt->keyVar->name)))
+		) {
 			$keyVarName = null;
-			if ($stmt->keyVar !== null
-				&& $stmt->keyVar instanceof Variable
-				&& is_string($stmt->keyVar->name)
-			) {
+			if ($stmt->keyVar instanceof Variable && is_string($stmt->keyVar->name)) {
 				$keyVarName = $stmt->keyVar->name;
 			}
 			$scope = $scope->enterForeach(
@@ -3762,6 +3763,18 @@ static function (): void {
 			) {
 				$scope = $scope->enterForeachKey($stmt->expr, $stmt->keyVar->name);
 				$vars[] = $stmt->keyVar->name;
+			} elseif ($stmt->keyVar !== null) {
+				$scope = $this->processAssignVar(
+					$scope,
+					$stmt->keyVar,
+					new GetIterableKeyTypeExpr($stmt->expr),
+					static function (): void {
+					},
+					ExpressionContext::createDeep(),
+					static fn (MutatingScope $scope): ExpressionResult => new ExpressionResult($scope, false, []),
+					true,
+				)->getScope();
+				$vars = array_merge($vars, $this->getAssignedVariables($stmt->keyVar));
 			}
 		}
 

tests/PHPStan/Analyser/AnalyserIntegrationTest.php

@@ -872,7 +872,7 @@ public function testBug7554(): void
 		$this->assertSame(27, $errors[1]->getLine());
 	}
 
-	public function testBug7737(): void
+	public function testBug7637(): void
 	{
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-7637.php');
 		$this->assertCount(2, $errors);
@@ -884,6 +884,12 @@ public function testBug7737(): void
 		$this->assertSame(54, $errors[1]->getLine());
 	}
 
+	public function testBug7737(): void
+	{
+		$errors = $this->runAnalyse(__DIR__ . '/data/bug-7737.php');
+		$this->assertNoErrors($errors);
+	}
+
 	/**
 	 * @param string[]|null $allAnalysedFiles
 	 * @return Error[]

tests/PHPStan/Analyser/data/bug-7737.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug7737;
+
+use function PHPStan\dumpType;
+
+function () {
+	$context = [
+		'values' => [1, 2, 3],
+	];
+	foreach ($context['values'] as $context["_key"] => $context["value"]) {
+		echo sprintf("Key: %s, Value: %s\n", $context["_key"], $context["value"]);
+	}
+
+	unset($context["_key"]);
+};
+
+function () {
+	$context = [
+		'values' => [1, 2, 3],
+	];
+	foreach ($context['values'] as $context["_key"] => $value) {
+		echo sprintf("Key: %s, Value: %s\n", $context["_key"], $value);
+	}
+
+	unset($context["_key"]);
+};