Handle optional keys in constant arrays for !in_array narrowing

When computing guaranteed values for the false context of in_array(),
exclude values from optional keys in constant arrays since they may
not be present at runtime. For array{a: 'a', c: 'c'}|array{a?: 'a', b: 'b'},
the value 'a' from the optional key should not be considered guaranteed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Type/Php/InArrayFunctionTypeSpecifyingExtension.php

@@ -18,6 +18,7 @@
 use PHPStan\Type\ArrayType;
 use PHPStan\Type\FunctionTypeSpecifyingExtension;
 use PHPStan\Type\MixedType;
+use PHPStan\Type\NeverType;
 use PHPStan\Type\TypeCombinator;
 use PHPStan\Type\UnionType;
 use function count;
@@ -123,7 +124,26 @@ public function specifyTypes(FunctionReflection $functionReflection, FuncCall $n
 			$innerTypes = $arrayType instanceof UnionType ? $arrayType->getTypes() : [$arrayType];
 			$innerValueTypes = [];
 			foreach ($innerTypes as $innerType) {
-				$innerValueTypes[] = $innerType->getIterableValueType();
+				$constantArrays = $innerType->getConstantArrays();
+				if (count($constantArrays) > 0) {
+					// Only include values from non-optional keys, since optional
+					// keys may not be present in the array at runtime.
+					$perArrayTypes = [];
+					foreach ($constantArrays as $constantArray) {
+						$guaranteedTypes = [];
+						foreach ($constantArray->getValueTypes() as $i => $valueType) {
+							if (!$constantArray->isOptionalKey($i)) {
+								$guaranteedTypes[] = $valueType;
+							}
+						}
+						$perArrayTypes[] = count($guaranteedTypes) > 0
+							? TypeCombinator::union(...$guaranteedTypes)
+							: new NeverType();
+					}
+					$innerValueTypes[] = TypeCombinator::intersect(...$perArrayTypes);
+				} else {
+					$innerValueTypes[] = $innerType->getIterableValueType();
+				}
 			}
 			if (count($innerValueTypes) > 0) {
 				$narrowingValueType = TypeCombinator::intersect(...$innerValueTypes);

tests/PHPStan/Analyser/nsrt/bug-14407.php

@@ -74,3 +74,15 @@ function () {
 		assertType('Bug14407\SomeEnum::A', $x);
 	}
 };
+
+/**
+ * @param 'a'|'b'|'c' $x
+ * @param array{a: 'a', c: 'c'}|array{a?:'a', b: 'b'} $a
+ */
+function testUnionWithOptionalKeys($x, $a): void
+{
+	assertType("array{a: 'a', c: 'c'}|array{a?: 'a', b: 'b'}", $a);
+	if (!\in_array($x, $a, true)) {
+		assertType("'a'|'b'|'c'", $x);
+	}
+};