Fix phpstan/phpstan#11054: [NAN] === mixed is always evaluated as false (#5321)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

src/Type/Constant/ConstantFloatType.php

@@ -99,6 +99,15 @@ public function toArrayKey(): Type
 		return new ConstantIntegerType((int) $this->value);
 	}
 
+	public function getFiniteTypes(): array
+	{
+		if (is_nan($this->value)) {
+			return [];
+		}
+
+		return [$this];
+	}
+
 	public function generalize(GeneralizePrecision $precision): Type
 	{
 		return new FloatType();

tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php

@@ -1161,4 +1161,15 @@ public function testPossiblyImpureTip(): void
 		]);
 	}
 
+	public function testBug11054(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-11054.php'], [
+			[
+				'Strict comparison using === between mixed and array{INF} will always evaluate to false.',
+				47,
+				'Type array{INF} has already been eliminated from mixed.',
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-11054.php

@@ -0,0 +1,58 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11054;
+
+class XXX {
+	public const DEF_VALUE = [NAN];
+	public const NO_VALUE  = [NAN];
+}
+
+class YYY
+{
+	public const LOSSLESS = [NAN];
+
+	/**
+	 * @param  string|int|mixed $substituteChar
+	 */
+	public static function convertEncoding (
+		string $str,
+		string $sourceEncoding,
+		string $targetEncoding,
+		$substituteChar = XXX::DEF_VALUE,
+		$defValue       = XXX::NO_VALUE
+	): string {
+		if ($substituteChar === XXX::DEF_VALUE) { // no error expected
+			return mb_convert_encoding($str, $targetEncoding, $sourceEncoding);
+		}
+
+		if ($substituteChar === self::LOSSLESS) { // no error expected
+			return $str;
+		}
+
+		return $str;
+	}
+}
+
+class InfTest {
+	public const DEF_VALUE = [INF];
+	public const NO_VALUE  = [INF];
+
+	/** @param mixed $v */
+	public static function test($v): void
+	{
+		if ($v === self::DEF_VALUE) { // no error expected
+			return;
+		}
+
+		if ($v === self::NO_VALUE) {} // error expected - INF === INF is true, so narrowing is correct
+	}
+}
+
+class SimpleTest {
+	/** @param mixed $v */
+	public static function test($v): void
+	{
+		if ($v === [NAN]) {} // no error expected
+		if ($v === [INF]) {} // no error expected
+	}
+}