Report invalid string offsets

Author: staabm

src/Type/StringType.php

@@ -63,7 +63,8 @@ public function isOffsetAccessLegal(): TrinaryLogic
 
 	public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 	{
-		return $offsetType->isInteger()->and(TrinaryLogic::createMaybe());
+		$zeroOrMore = IntegerRangeType::fromInterval(0, null);
+		return $zeroOrMore->isSuperTypeOf($offsetType)->result->and(TrinaryLogic::createMaybe());
 	}
 
 	public function getOffsetValueType(Type $offsetType): Type

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -754,4 +754,30 @@ public function testBug2634(): void
 		$this->analyse([__DIR__ . '/data/bug-2634.php'], []);
 	}
 
+	public function testBug11946(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-11946.php'], [
+			[
+				'Offset -1 does not exist on string.',
+				21,
+			],
+			[
+				'Offset -1 does not exist on numeric-string.',
+				22,
+			],
+			[
+				'Offset -1 does not exist on non-empty-string.',
+				23,
+			],
+			[
+				'Offset -1 does not exist on non-falsy-string.',
+				24,
+			],
+			[
+				'Offset -1 does not exist on string.',
+				25,
+			],
+		]);
+	}
+
 }

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

@@ -0,0 +1,33 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11946;
+
+class HelloWorld
+{
+	/**
+	 * @param numeric-string $numericS
+	 * @param non-empty-string $nonEmpty
+	 * @param non-falsy-string $nonFalsy
+	 * @param lowercase-string $lowerCase
+	 */
+	public function nonExistentStringOffset(
+		string $s,
+		string $numericS,
+		string $nonEmpty,
+		string $nonFalsy,
+		string $lowerCase,
+	)
+	{
+		echo $s[-1];
+		echo $numericS[-1];
+		echo $nonEmpty[-1];
+		echo $nonFalsy[-1];
+		echo $lowerCase[-1];
+
+		echo $s[0];
+		echo $numericS[0];
+		echo $nonEmpty[0];
+		echo $nonFalsy[0];
+		echo $lowerCase[0];
+	}
+}