Fix phpstan/phpstan#11705: Value of a variable is forgotten in case where it ought to be known with certainty

src/Analyser/MutatingScope.php

@@ -1043,7 +1043,24 @@
 			&& !$node instanceof Expr\ArrowFunction
 			&& $this->hasExpressionType($node)->yes()
 		) {
-			return $this->expressionTypes[$exprString]->getType();
+			$type = $this->expressionTypes[$exprString]->getType();
+
+			if ($node instanceof Expr\ArrayDimFetch && $node->dim !== null) {
+				$dimType = $this->getType($node->dim);
+				if ($dimType->isConstantScalarValue()->yes()) {
+					$arrayType = $this->getType($node->var);
+					$offsetValueType = $arrayType->getOffsetValueType($dimType);
+					if (
+						!$offsetValueType instanceof ErrorType
+						&& $type->isSuperTypeOf($offsetValueType)->yes()
+						&& !$offsetValueType->isSuperTypeOf($type)->yes()
+					) {
+						$type = $offsetValueType;
+					}
+				}
+			}
+
+			return $type;
 		}
 
 		/** @var ExprHandler<Expr> $exprHandler */

tests/PHPStan/Analyser/nsrt/bug-11705.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11705;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param array{'name':string,'owners':array<int,string>} $theInput
+ * @param array<int,string> $theTags
+ */
+function example(array $theInput, array $theTags): void
+{
+	foreach ($theTags as $tag) {
+		if (!array_key_exists($tag, $theInput)) {
+			continue;
+		}
+		switch ($tag) {
+			case 'name':
+				assertType("'name'", $tag);
+				assertType('string', $theInput[$tag]);
+				if ($tag === 'name') {
+					echo "Of course it is...";
+				}
+				assertType("'name'", $tag);
+				assertType('string', $theInput[$tag]);
+				break;
+			default:
+				// fall out
+		}
+	}
+}