Fix "Offset (int|string) might not exist on array" after array_keys($arr)

Author: staabm

src/Analyser/NodeScopeResolver.php

@@ -6521,6 +6521,23 @@ private function enterForeach(MutatingScope $scope, MutatingScope $originalScope
 			}
 		}
 
+		if (
+			$stmt->expr instanceof FuncCall
+			&& $stmt->expr->name instanceof Name
+			&& $stmt->expr->name->toLowerString() === 'array_keys'
+			&& $stmt->valueVar instanceof Variable
+		) {
+			$args = $stmt->expr->getArgs();
+			if (count($args) >= 1) {
+				$arrayArg = $args[0]->value;
+				$scope = $scope->assignExpression(
+					new ArrayDimFetch($arrayArg, $stmt->valueVar),
+					$scope->getType($arrayArg)->getIterableValueType(),
+					$scope->getNativeType($arrayArg)->getIterableValueType(),
+				);
+			}
+		}
+
 		return $this->processVarAnnotation($scope, $vars, $stmt);
 	}
 

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -1000,4 +1000,11 @@ public function testBug10492(): void
 		]);
 	}
 
+	public function testBug12926(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12926.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-12926.php

@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+namespace Bug12926;
+
+class HelloWorld
+{
+	public function sayHello(array $arr): void
+	{
+		foreach (array_keys($arr) as $key) {
+			var_dump($arr[$key]);
+		}
+	}
+}