Fix "array_rand() - offset might not exists"

src/Analyser/TypeSpecifier.php

@@ -687,6 +687,34 @@ public function specifyTypesInCondition(
 			if ($context->null()) {
 				$specifiedTypes = $this->specifyTypesInCondition($scope->exitFirstLevelStatements(), $expr->expr, $context)->setRootExpr($expr);
 
+				// infer $arr[$key] after $key = array_rand($arr)
+				if (
+					$expr->expr instanceof FuncCall
+					&& $expr->expr->name instanceof Name
+					&& in_array($expr->expr->name->toLowerString(), ['array_rand'], true)
+					&& count($expr->expr->getArgs()) >= 1
+				) {
+					$numArg = null;
+					$arrayArg = $expr->expr->getArgs()[0]->value;
+					if (count($expr->expr->getArgs()) > 1) {
+						$numArg = $expr->expr->getArgs()[1]->value;
+					}
+					$one = new ConstantIntegerType(1);
+					$arrayType = $scope->getType($arrayArg);
+
+					if (
+						$arrayType->isArray()->yes()
+						&& $arrayType->isIterableAtLeastOnce()->yes()
+						&& ($numArg === null || $one->isSuperTypeOf($scope->getType($numArg))->yes())
+					) {
+						$dimFetch = new ArrayDimFetch($arrayArg, $expr->var);
+
+						return $specifiedTypes->unionWith(
+							$this->create($dimFetch, $arrayType->getIterableValueType(), TypeSpecifierContext::createTrue(), $scope),
+						);
+					}
+				}
+
 				// infer $arr[$key] after $key = array_key_first/last($arr)
 				if (
 					$expr->expr instanceof FuncCall

src/Rules/Arrays/NonexistentOffsetInArrayDimFetchRule.php

@@ -14,6 +14,7 @@
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Rules\RuleLevelHelper;
 use PHPStan\TrinaryLogic;
+use PHPStan\Type\Constant\ConstantIntegerType;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\Type;
 use PHPStan\Type\VerbosityLevel;
@@ -129,6 +130,33 @@ public function processNode(Node $node, Scope $scope): array
 			}
 		}
 
+		if (
+			$node->dim instanceof Node\Expr\FuncCall
+			&& $node->dim->name instanceof Node\Name
+			&& $node->dim->name->toLowerString() === 'array_rand'
+			&& count($node->dim->getArgs()) >= 1
+		) {
+			$numArg = null;
+			$arrayArg = $node->dim->getArgs()[0]->value;
+			if (count($node->dim->getArgs()) > 1) {
+				$numArg = $node->dim->getArgs()[1]->value;
+			}
+			$one = new ConstantIntegerType(1);
+			$arrayType = $scope->getType($arrayArg);
+
+			if (
+				$arrayArg instanceof Node\Expr\Variable
+				&& $node->var instanceof Node\Expr\Variable
+				&& is_string($arrayArg->name)
+				&& $arrayArg->name === $node->var->name
+				&& $arrayType->isArray()->yes()
+				&& $arrayType->isIterableAtLeastOnce()->yes()
+				&& ($numArg === null || $one->isSuperTypeOf($scope->getType($numArg))->yes())
+			) {
+				return [];
+			}
+		}
+
 		if (
 			$node->dim instanceof Node\Expr\BinaryOp\Minus
 			&& $node->dim->left instanceof Node\Expr\FuncCall

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -69,6 +69,7 @@ private static function findTestFiles(): iterable
 		}
 
 		yield __DIR__ . '/../Rules/Methods/data/bug-6856.php';
+		yield __DIR__ . '/../Rules/Arrays/data/bug-12981.php';
 
 		if (PHP_VERSION_ID < 80000) {
 			yield __DIR__ . '/data/explode-php74.php';

tests/PHPStan/Rules/Arrays/InvalidKeyInArrayDimFetchRuleTest.php

@@ -116,4 +116,26 @@ public function testBug12273(): void
 		]);
 	}
 
+	public function testBug12981(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-12981.php'], [
+			[
+				'Invalid array key type array<int, int|string>.',
+				31,
+			],
+			[
+				'Invalid array key type array<int, int|string>.',
+				33,
+			],
+			[
+				'Possibly invalid array key type array<int, int|string>|int|string.',
+				39,
+			],
+			[
+				'Possibly invalid array key type array<int, int|string>|int|string.',
+				41,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -933,6 +933,22 @@ public function testBug12593(): void
 		$this->analyse([__DIR__ . '/data/bug-12593.php'], []);
 	}
 
+	public function testBug12981(): void
+	{
+		$this->reportPossiblyNonexistentGeneralArrayOffset = true;
+
+		$this->analyse([__DIR__ . '/data/bug-12981.php'], [
+			[
+				'Offset array<int, int|string>|int|string might not exist on non-empty-array<bool|float|int|string>.',
+				39,
+			],
+			[
+				'Offset array<int, int|string>|int|string might not exist on non-empty-array<bool|float|int|string>.',
+				41,
+			],
+		]);
+	}
+
 	public function testBugObject(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-object.php'], [

tests/PHPStan/Rules/Arrays/data/bug-12981.php

@@ -0,0 +1,60 @@
+<?php declare(strict_types = 1);
+
+namespace Bug12981;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	/** @param non-empty-array<scalar> $arr */
+	public function sayHello(array $arr): void
+	{
+		echo $arr[array_rand($arr)];
+		$randIndex = array_rand($arr);
+		assertType('bool|float|int|string', $arr[$randIndex]);
+		echo $arr[$randIndex];
+	}
+
+	/** @param non-empty-array<scalar> $arr */
+	public function sayHello1(array $arr): void
+	{
+		$num = 1;
+		echo $arr[array_rand($arr, $num)];
+		$randIndex = array_rand($arr, $num);
+		echo $arr[$randIndex];
+	}
+
+	/** @param non-empty-array<scalar> $arr */
+	public function sayHello2(array $arr): void
+	{
+		$num = 5;
+		echo $arr[array_rand($arr, $num)];
+		$randIndex = array_rand($arr, $num);
+		echo $arr[$randIndex];
+	}
+
+	/** @param non-empty-array<scalar> $arr */
+	public function sayHello4(array $arr, int $num): void
+	{
+		echo $arr[array_rand($arr, $num)];
+		$randIndex = array_rand($arr, $num);
+		echo $arr[$randIndex];
+	}
+
+	public function sayHello5(): void
+	{
+		$arr = [
+			1 => true,
+			2 => false,
+			'a' => 'hello',
+		];
+		assertType("'hello'|bool", $arr[array_rand($arr)]);
+
+		$arr = [
+			1 => true,
+			2 => null,
+			'a' => 'hello',
+		];
+		assertType("'hello'|true|null", $arr[array_rand($arr)]);
+	}
+}