Fix phpstan/phpstan#2572: Optional templated args not provided cause unbound template errors (#5175)

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/Reflection/GenericParametersAcceptorResolver.php

@@ -10,6 +10,7 @@
 use PHPStan\Type\Generic\TemplateTypeMap;
 use PHPStan\Type\Generic\TemplateTypeVarianceMap;
 use PHPStan\Type\MixedType;
+use PHPStan\Type\NeverType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
 use function array_key_exists;
@@ -61,6 +62,8 @@ public static function resolve(array $argTypes, ParametersAcceptor $parametersAc
 				$argType = $namedArgTypes[$param->getName()];
 			} elseif ($param->getDefaultValue() !== null) {
 				$argType = $param->getDefaultValue();
+			} elseif ($param->isVariadic()) {
+				$argType = new NeverType(true);
 			} else {
 				continue;
 			}

tests/PHPStan/Analyser/nsrt/bug-2572.php

@@ -0,0 +1,49 @@
+<?php declare(strict_types = 1);
+
+namespace Bug2572Nsrt;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template TE
+ * @template TR
+ *
+ * @param TE $elt
+ * @param TR ...$elts
+ *
+ * @return TE|TR
+ */
+function collect($elt, ...$elts) {
+	$ret = $elt;
+	foreach ($elts as $item) {
+		if (rand(0, 1)) {
+			$ret = $item;
+		}
+	}
+	return $ret;
+}
+
+assertType("'a'", collect("a"));
+assertType("'a'|'b'|'c'", collect("a", "b", "c"));
+
+/**
+ * @template TValue
+ * @template TArgs
+ *
+ * @param  TValue|\Closure(TArgs): TValue  $value
+ * @param  TArgs  ...$args
+ * @return TValue
+ */
+function value($value, ...$args)
+{
+	return $value instanceof \Closure ? $value(...$args) : $value;
+}
+
+assertType("'foo'", value('foo'));
+assertType("'foo'", value('foo', 42));
+assertType('42', value(fn () => 42));
+assertType('42', value(function ($foo) {
+	assertType('true', $foo);
+
+	return 42;
+}, true));

tests/PHPStan/Analyser/nsrt/bug-7704.php

@@ -0,0 +1,30 @@
+<?php declare(strict_types = 1);
+
+namespace Bug7704;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T
+ * @template TRest
+ *
+ * @param T $first
+ * @param TRest ...$rest
+ *
+ * @return T|TRest
+ */
+function intersection($first, ...$rest)
+{
+	$ret = $first;
+	foreach ($rest as $item) {
+		if (rand(0, 1)) {
+			$ret = $item;
+		}
+	}
+	return $ret;
+}
+
+assertType("'a'", intersection("a"));
+assertType("'a'|'b'|'c'", intersection("a", "b", "c"));
+assertType('1', intersection(1));
+assertType('1|2|3', intersection(1, 2, 3));

tests/PHPStan/Analyser/nsrt/bug-9360.php

@@ -0,0 +1,24 @@
+<?php declare(strict_types = 1);
+
+namespace Bug9360;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template T of string|bool
+ *
+ * @param T ...$args
+ *
+ * @return (T is string ? string : bool)
+ */
+function environment(string|bool ...$args): string|bool
+{
+	if (count($args) === 0) {
+		return true;
+	}
+	return (string) $args[0];
+}
+
+assertType('string', environment());
+assertType('string', environment('APP_ENV'));
+assertType('string', environment('APP_ENV', 'production'));

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -2691,6 +2691,21 @@ public function testBug8936(): void
 		$this->analyse([__DIR__ . '/data/bug-8936.php'], []);
 	}
 
+	public function testBug2572(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-2572.php'], []);
+	}
+
+	public function testBug7704(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-7704.php'], []);
+	}
+
+	public function testBug9360(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-9360.php'], []);
+	}
+
 	public function testDumpFunctions(): void
 	{
 		$this->analyse([__DIR__ . '/data/dump-functions.php'], [