Fix foreach type narrowing for constant string arrays

- After foreach over constant string arrays like ['need', 'field'], propagate per-element type narrowings (HasOffsetValueType) to variables narrowed inside the loop body
- Added logic in NodeScopeResolver post-foreach processing to detect variables whose dim-fetch expressions were narrowed (e.g. via isset + is_string) and apply HasOffsetValueType for each constant array element
- Guards against false positives by checking the variable wasn't modified (assigned) in the body and that the dim-fetch narrowing is new (not pre-existing)
- New regression test in tests/PHPStan/Analyser/nsrt/bug-11533.php

Author: phpstan-bot

src/Analyser/NodeScopeResolver.php

@@ -137,6 +137,7 @@
 use PHPStan\Rules\Properties\ReadWritePropertiesExtensionProvider;
 use PHPStan\ShouldNotHappenException;
 use PHPStan\TrinaryLogic;
+use PHPStan\Type\Accessory\HasOffsetValueType;
 use PHPStan\Type\ArrayType;
 use PHPStan\Type\ClosureType;
 use PHPStan\Type\FileTypeMapper;
@@ -1393,6 +1394,85 @@ public function processStmtNode(
 				$finalScope = $finalScope->assignExpression(new ForeachValueByRefExpr($stmt->valueVar), new MixedType(), new MixedType());
 			}
 
+			// Propagate per-element type narrowings from foreach over constant arrays
+			if (
+				$context->isTopLevel()
+				&& count($breakExitPoints) === 0
+				&& $isIterableAtLeastOnce->yes()
+				&& !$stmt->byRef
+				&& $stmt->valueVar instanceof Variable && is_string($stmt->valueVar->name)
+				&& $exprType->isConstantArray()->yes()
+			) {
+				$constantArrays = $exprType->getConstantArrays();
+				if (
+					count($constantArrays) === 1
+					&& count($constantArrays[0]->getValueTypes()) > 0
+					&& count($constantArrays[0]->getValueTypes()) <= 32
+				) {
+					$constantArray = $constantArrays[0];
+					$offsetValueTypes = [];
+					foreach ($constantArray->getValueTypes() as $valueType) {
+						$constantStrings = $valueType->getConstantStrings();
+						if (count($constantStrings) === 1) {
+							$offsetValueTypes[] = $constantStrings[0];
+							continue;
+						}
+						$offsetValueTypes = [];
+						break;
+					}
+
+					if (count($offsetValueTypes) > 0) {
+						$bodyEndScope = $finalScopeResult->getScope();
+						$loopVar = $stmt->valueVar;
+						foreach ($finalScope->getDefinedVariables() as $varName) {
+							if ($varName === $loopVar->name) {
+								continue;
+							}
+							$varExpr = new Variable($varName);
+							$varType = $finalScope->getType($varExpr);
+							if (!$varType->isArray()->yes()) {
+								continue;
+							}
+
+							// Skip if the variable was modified (assigned) in the body
+							$preLoopVarType = $scope->getType($varExpr);
+							if (!$preLoopVarType->equals($varType)) {
+								continue;
+							}
+
+							$dimFetch = new ArrayDimFetch($varExpr, $loopVar);
+							// Only proceed if the body specifically narrowed $var[$field]
+							if (!$bodyEndScope->hasExpressionType($dimFetch)->yes()) {
+								continue;
+							}
+							// Skip if the pre-loop scope already had this expression type
+							if ($scope->hasExpressionType($dimFetch)->yes()) {
+								continue;
+							}
+
+							$dimFetchType = $bodyEndScope->getType($dimFetch);
+							$genericValueType = $varType->getIterableValueType();
+
+							if ($dimFetchType->equals($genericValueType)) {
+								continue;
+							}
+
+							$accessories = [];
+							foreach ($offsetValueTypes as $offsetType) {
+								$accessories[] = new HasOffsetValueType($offsetType, $dimFetchType);
+							}
+							$narrowedVarType = TypeCombinator::intersect($varType, ...$accessories);
+							$finalScope = $finalScope->assignVariable(
+								$varName,
+								$narrowedVarType,
+								TypeCombinator::intersect($finalScope->getNativeType($varExpr), ...$accessories),
+								TrinaryLogic::createYes(),
+							);
+						}
+					}
+				}
+			}
+
 			return new InternalStatementResult(
 				$finalScope,
 				$finalScopeResult->hasYield() || $condResult->hasYield(),

tests/PHPStan/Analyser/nsrt/bug-11533.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11533;
+
+use function PHPStan\Testing\assertType;
+
+/** @param mixed[] $param */
+function hello(array $param): void
+{
+	foreach (['need', 'field'] as $field) {
+		if (!isset($param[$field]) || !is_string($param[$field])) {
+			throw new \Exception();
+		}
+	}
+	assertType("non-empty-array<mixed>&hasOffsetValue('field', string)&hasOffsetValue('need', string)", $param);
+}
+
+/** @param array<string, mixed> $data */
+function helloWithArrayKeyExists(array $data): void
+{
+	foreach (['name', 'email'] as $key) {
+		if (!array_key_exists($key, $data) || !is_string($data[$key])) {
+			throw new \Exception();
+		}
+	}
+	assertType("non-empty-array<string, mixed>&hasOffsetValue('email', string)&hasOffsetValue('name', string)", $data);
+}