Ask an unresolved template argument whether it is a subtype of a union

UnionType::isSuperTypeOf() compared an UnresolvedTemplateArgumentType
member by member, so a marker standing for int|string was only maybe a
subtype of BackedEnum|int|string. A closure whose inferred signature settled
keeps its markers in the second pass, and a generic callee inferring its
template type from that closure's parameter lost it - "Unable to resolve
the template type" and a closure it then rejected.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VpbB99tJfUmeArX74xqvHv

Author: ondrejmirtes

src/Type/UnionType.php

@@ -35,6 +35,7 @@
 use PHPStan\Type\Generic\TemplateTypeMap;
 use PHPStan\Type\Generic\TemplateTypeVariance;
 use PHPStan\Type\Generic\TemplateUnionType;
+use PHPStan\Type\Generic\UnresolvedTemplateArgumentType;
 use PHPStan\Type\Traits\NonGeneralizableTypeTrait;
 use Throwable;
 use function array_diff_assoc;
@@ -334,6 +335,8 @@ public function isSuperTypeOf(Type $otherType): IsSuperTypeOfResult
 			|| ($otherType instanceof IterableType && !$otherType instanceof TemplateIterableType)
 			|| $otherType instanceof NeverType
 			|| $otherType instanceof IntegerRangeType
+			// stands for its delegate, which can itself be a union
+			|| $otherType instanceof UnresolvedTemplateArgumentType
 		) {
 			return $otherType->isSubTypeOf($this);
 		}

tests/PHPStan/Analyser/nsrt/closure-signature-from-usages.php

@@ -38,6 +38,16 @@ function takesMixed(mixed $m): void
 {
 }
 
+/**
+ * @template T of \BackedEnum|int|string
+ * @param \Closure(T): string $cb
+ * @return list<T>
+ */
+function takesConvertor(\Closure $cb): array
+{
+	return [];
+}
+
 function takesBareCallable(callable $cb): void
 {
 }
@@ -486,4 +496,13 @@ public function returnContextualTypingArrow(): void
 		takesFactory($c);
 	}
 
+	public function settledClosureSentToGenericTarget(): void
+	{
+		$convertor = static function (int|string $value): string {
+			assertType('int|string', $value);
+			return 'x' . $value;
+		};
+		assertType('list<int|string>', takesConvertor($convertor));
+	}
+
 }

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -914,6 +914,7 @@ public function testBug3660(): void
 		]);
 	}
 
+	#[RequiresPhp('>= 8.0.0')]
 	public function testClosureSignatureFromUsages(): void
 	{
 		$this->analyse([__DIR__ . '/data/closure-signature-from-usages.php'], [

tests/PHPStan/Rules/Functions/data/closure-signature-from-usages.php

@@ -1,4 +1,4 @@
-<?php
+<?php // lint >= 8.0
 
 namespace ClosureSignatureFromUsagesRule;
 
@@ -36,3 +36,20 @@ function (): void {
 	};
 	takesIntToStringCallback($identity);
 };
+
+/**
+ * @template T of \BackedEnum|int|string
+ * @param \Closure(T): string $cb
+ * @return list<T>
+ */
+function takesConvertor(\Closure $cb): array
+{
+	return [];
+}
+
+function (): void {
+	$convertor = static function (int|string $value): string {
+		return 'x' . $value;
+	};
+	takesConvertor($convertor);
+};

turbo-ext/src/UnionType.cpp

@@ -767,7 +767,9 @@ class UnionType
 			}
 		}
 		if (!delegate) {
-			delegate = instanceof_function(Z_OBJCE_P(otherType), pt_ce_never_type) || instanceof_function(Z_OBJCE_P(otherType), pt_ce_integer_range_type);
+			delegate = instanceof_function(Z_OBJCE_P(otherType), pt_ce_never_type) || instanceof_function(Z_OBJCE_P(otherType), pt_ce_integer_range_type)
+				// stands for its delegate, which can itself be a union
+				|| instanceof_function(Z_OBJCE_P(otherType), pt_ce_unresolved_template_argument_type);
 		}
 		if (delegate) return pt_type_op(Z_OBJ_P(otherType), PT_OP_IS_SUB_TYPE_OF, 1, &selfZv);