Report maybe invalid string int-offsets

Author: staabm

src/Rules/Arrays/NonexistentOffsetInArrayDimFetchCheck.php

@@ -10,6 +10,7 @@
 use PHPStan\Rules\RuleLevelHelper;
 use PHPStan\Type\BenevolentUnionType;
 use PHPStan\Type\ErrorType;
+use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeUtils;
 use PHPStan\Type\UnionType;
@@ -65,6 +66,15 @@ public function check(
 		if ($this->reportMaybes) {
 			$report = false;
 
+			$zeroOrMore = IntegerRangeType::fromInterval(0, null);
+			if (
+				$type->isString()->yes()
+				&& $dimType->isInteger()->yes()
+				&& !$zeroOrMore->isSuperTypeOf($dimType)->yes()
+			) {
+				$report = true;
+			}
+
 			if ($type instanceof BenevolentUnionType) {
 				$flattenedTypes = [$type];
 			} else {

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -803,6 +803,26 @@ public function testBug11946(): void
 				'Offset -1 does not exist on string.',
 				25,
 			],
+			[
+				'Offset int<-5, 5> might not exist on string.',
+				45
+			],
+			[
+				'Offset int<-5, 5> might not exist on numeric-string.',
+				46
+			],
+			[
+				'Offset int<-5, 5> might not exist on non-empty-string.',
+				47
+			],
+			[
+				'Offset int<-5, 5> might not exist on non-falsy-string.',
+				48
+			],
+			[
+				'Offset int<-5, 5> might not exist on string.',
+				49
+			],
 		]);
 	}
 

tests/PHPStan/Rules/Arrays/data/bug-11946.php

@@ -23,11 +23,29 @@ public function nonExistentStringOffset(
 		echo $nonEmpty[-1];
 		echo $nonFalsy[-1];
 		echo $lowerCase[-1];
+	}
 
-		echo $s[0];
-		echo $numericS[0];
-		echo $nonEmpty[0];
-		echo $nonFalsy[0];
-		echo $lowerCase[0];
+	/**
+	 * @param numeric-string $numericS
+	 * @param non-empty-string $nonEmpty
+	 * @param non-falsy-string $nonFalsy
+	 * @param lowercase-string $lowerCase
+	 *
+	 * @param int<-5, 5> $maybeWrong
+	 */
+	public function maybeNonExistentStringOffset(
+		string $s,
+		string $numericS,
+		string $nonEmpty,
+		string $nonFalsy,
+		string $lowerCase,
+	    int $maybeWrong
+	)
+	{
+		echo $s[$maybeWrong];
+		echo $numericS[$maybeWrong];
+		echo $nonEmpty[$maybeWrong];
+		echo $nonFalsy[$maybeWrong];
+		echo $lowerCase[$maybeWrong];
 	}
 }