Fix containsNan to handle union array types and optional keys

When a type is a union of constant arrays (e.g. array{NAN}|array{1}),
containsNan should only return true if ALL variants contain NAN, not
just any of them. Also skip optional keys since absent optional entries
mean the array might not actually contain NAN.

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

Author: phpstan-bot

src/Reflection/InitializerExprTypeResolver.php

@@ -2076,12 +2076,30 @@ private function containsNan(Type $type): bool
 			return true;
 		}
 
-		foreach ($type->getConstantArrays() as $constantArray) {
-			foreach ($constantArray->getValueTypes() as $valueType) {
-				if ($this->containsNan($valueType)) {
-					return true;
+		$constantArrays = $type->getConstantArrays();
+		if ($constantArrays !== [] && $type->isConstantArray()->yes()) {
+			foreach ($constantArrays as $constantArray) {
+				if (!$this->constantArrayContainsNan($constantArray)) {
+					return false;
 				}
 			}
+
+			return true;
+		}
+
+		return false;
+	}
+
+	private function constantArrayContainsNan(ConstantArrayType $constantArray): bool
+	{
+		$optionalKeys = $constantArray->getOptionalKeys();
+		foreach ($constantArray->getValueTypes() as $index => $valueType) {
+			if (in_array($index, $optionalKeys, true)) {
+				continue;
+			}
+			if ($this->containsNan($valueType)) {
+				return true;
+			}
 		}
 
 		return false;

tests/PHPStan/Rules/Comparison/data/bug-14394.php

@@ -10,4 +10,10 @@ public static function test(float $v1, array $v2): void {
 		if ($v2 == [NAN]) { echo "never reached\n"; }
 		if ($v2 === [NAN]) { echo "never reached\n"; }
 	}
+
+	/** @param array{NAN}|array{1} $v */
+	public static function testUnionArrayNotAlwaysFalse(array $v): void {
+		if ($v === [1]) { echo "maybe reached\n"; }
+		if ($v == [1]) { echo "maybe reached\n"; }
+	}
 }