Support IntegerRangeType in ConstantStringType offset-value-type handling

Author: staabm

src/Type/Constant/ConstantStringType.php

@@ -345,23 +345,43 @@ public function isLiteralString(): TrinaryLogic
 
 	public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 	{
-		if ($offsetType instanceof ConstantIntegerType) {
-			return TrinaryLogic::createFromBoolean(
-				$offsetType->getValue() < strlen($this->value),
-			);
+		if ($offsetType->isInteger()->yes()) {
+			$strLenType = IntegerRangeType::fromInterval(0, strlen($this->value) - 1);
+			return $strLenType->isSuperTypeOf($offsetType);
 		}
 
 		return parent::hasOffsetValueType($offsetType);
 	}
 
 	public function getOffsetValueType(Type $offsetType): Type
 	{
-		if ($offsetType instanceof ConstantIntegerType) {
-			if ($offsetType->getValue() < strlen($this->value)) {
-				return new self($this->value[$offsetType->getValue()]);
+		if ($offsetType->isInteger()->yes()) {
+			if ($offsetType instanceof ConstantIntegerType) {
+				if ($offsetType->getValue() < strlen($this->value)) {
+					return new self($this->value[$offsetType->getValue()]);
+				}
+
+				return new ErrorType();
 			}
 
-			return new ErrorType();
+			$strLenType = IntegerRangeType::fromInterval(0, strlen($this->value) - 1);
+			$intersected = TypeCombinator::intersect($strLenType, $offsetType);
+			if ($intersected instanceof IntegerRangeType) {
+				$finiteTypes = $intersected->getFiniteTypes();
+				if ($finiteTypes === []) {
+					return parent::getOffsetValueType($offsetType);
+				}
+
+				$chars = [];
+				foreach ($finiteTypes as $constantInteger) {
+					$chars[] = new self($this->value[$constantInteger->getValue()]);
+				}
+				if (!$strLenType->isSuperTypeOf($offsetType)->yes()) {
+					$chars[] = new self('');
+				}
+
+				return TypeCombinator::union(...$chars);
+			}
 		}
 
 		return parent::getOffsetValueType($offsetType);

tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php

@@ -2904,7 +2904,7 @@ public function dataBinaryOperations(): array
 				'$fooString[4]',
 			],
 			[
-				'non-empty-string',
+				"''|'f'|'o'",
 				'$fooString[$integer]',
 			],
 			[

tests/PHPStan/Analyser/nsrt/string-offsets.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace StringOffsets;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param int<1, 3> $oneToThree
+ * @param int<3, 10> $threeToTen
+ * @param int<10, max> $tenOrMore
+ * @param int<-10, -5> $negative
+ *
+ * @return void
+ */
+function doFoo($oneToThree, $threeToTen, $tenOrMore, $negative, int $i) {
+	$s = "world";
+	if (rand(0, 1)) {
+		$s = "hello";
+	}
+
+	assertType("''|'d'|'e'|'h'|'l'|'o'|'r'|'w'", $s[$i]);
+
+	assertType("'h'|'w'", $s[0]);
+
+	assertType("'e'|'l'|'o'|'r'", $s[$oneToThree]);
+	assertType('*ERROR*', $s[$tenOrMore]);
+	assertType("''|'d'|'l'|'o'", $s[$threeToTen]);
+	assertType("*ERROR*", $s[$negative]);
+
+	$longString = "myF5HnJv799kWf8VRI7g97vwnABTwN9y2CzAVELCBfRqyqkdTzXg7BkGXcwuIOscAiT6tSuJGzVZOJnYXvkiKQzYBNjjkCPOzSKXR5YHRlVxV1BetqZz4XOmaH9mtacJ9azNYL6bNXezSBjX13BSZy02SK2udzQLbTPNQwlKadKaNkUxjtWegkb8QDFaXbzH1JENVSLVH0FYd6POBU82X1xu7FDDKYLzwsWJHBGVhG8iugjEGwLj22x5ViosUyKR";
+	assertType("non-empty-string", $longString[$i]);
+}