Added ArrayFlipFunctionReturnTypeExtension, Cover non-empty-array in array_flip

conf/config.neon

@@ -928,6 +928,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\ArrayFlipFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\ArrayKeyDynamicReturnTypeExtension
 		tags:

src/Type/Php/ArrayFlipFunctionReturnTypeExtension.php

@@ -0,0 +1,70 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\Type\Accessory\NonEmptyArrayType;
+use PHPStan\Type\ArrayType;
+use PHPStan\Type\Constant\ConstantIntegerType;
+use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\IntegerType;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+
+class ArrayFlipFunctionReturnTypeExtension implements \PHPStan\Type\DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'array_flip';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): Type
+	{
+		if (count($functionCall->args) !== 1) {
+			return ParametersAcceptorSelector::selectSingle($functionReflection->getVariants())->getReturnType();
+		}
+
+		$array = $functionCall->args[0]->value;
+		$argType = $scope->getType($array);
+
+		if ($argType->isArray()->yes()) {
+			$keyType = $argType->getIterableKeyType();
+			$itemType = $argType->getIterableValueType();
+
+			// make sure items, which get turned into keys contain only valid types
+			$itemType = $this->sanitizeKeyTypes($itemType);
+
+			if ($itemType !== null) {
+				$flippedArrayType = new ArrayType(
+					$itemType,
+					$keyType
+				);
+
+				if ($argType->isIterableAtLeastOnce()->yes()) {
+					$flippedArrayType = TypeCombinator::intersect($flippedArrayType, new NonEmptyArrayType());
+				}
+
+				return $flippedArrayType;
+			}
+		}
+
+		return ParametersAcceptorSelector::selectSingle($functionReflection->getVariants())->getReturnType();
+	}
+
+	private function sanitizeKeyTypes(Type $type): ?Type
+	{
+		if (
+			!$type instanceof IntegerType
+			&& !$type instanceof StringType
+		) {
+			return null;
+		}
+
+		return $type;
+	}
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -264,6 +264,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Methods/data/infer-array-key.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/offset-value-after-assign.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-2112.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/array-flip.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/array-map-closure.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/array-sum.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-4573.php');

tests/PHPStan/Analyser/data/array-flip.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace ArrayFlip;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param int[] $integerList
+ */
+function foo($integerList)
+{
+	$flip = array_flip($integerList);
+	assertType('array<int, (int|string)>', $flip);
+}
+
+/**
+ * @param mixed[] $list
+ */
+function foo3($list)
+{
+	$flip = array_flip($list);
+
+	if (PHP_VERSION_ID < 80000) {
+		assertType('array|null', $flip);
+	} else {
+		assertType('array', $flip);
+	}
+}
+
+/**
+ * @param array<int, 1|2|3> $list
+ */
+function foo4($array)
+{
+	$flip = array_flip($array);
+	assertType('array<1|2|3, int>', $flip);
+}
+
+
+/**
+ * @param array<1|2|3, string> $list
+ */
+function foo5($array)
+{
+	$flip = array_flip($array);
+	assertType('array<string, 1|2|3>', $flip);
+}

tests/PHPStan/Analyser/data/non-empty-array.php

@@ -47,5 +47,7 @@ public function arrayFunctions($array, $list): void
 		assertType('array&nonEmpty', array_merge([], $array));
 		assertType('array&nonEmpty', array_merge($array, []));
 		assertType('array&nonEmpty', array_merge($array, $array));
+
+		assertType('array<(int|string)>&nonEmpty', array_flip($array));
 	}
 }