Use generic parameter defaults to constrain empty nested collections

ondrejmirtes · Sep 7, 2026 · Sep 1, 2026 · Sep 1, 2026 · Sep 1, 2026 · Sep 6, 2026
commit 952645bbb33a134a827a4b9d1982cbf13a61f629
diff --git a/src/Analyser/Generics/TemplateArgumentObserver.php b/src/Analyser/Generics/TemplateArgumentObserver.php
@@ -4,6 +4,7 @@
 
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Type\Generic\TemplateType;
+use PHPStan\Type\Generic\TemplateTypeHelper;
 use PHPStan\Type\Generic\TemplateTypeVariance;
 use PHPStan\Type\Generic\UnresolvedTemplateArgumentType;
 use PHPStan\Type\MixedType;
@@ -122,6 +123,13 @@ private function observeSend(TemplateArgumentConstraints $constraints, Type $dec
 					$constraints = $this->observeSend($constraints, $declaredArgument, $argument, $isCallArgument);
 					continue;
 				}
+				if (
+					$isCallArgument
+					&& ($argument->getInitialType() === null || $argument->getInitialType() instanceof NeverType)
+					&& self::hasOnlyInferableTemplates($declaredArgument)
+				) {
+					$declaredArgument = TemplateTypeHelper::resolveToDefaults($declaredArgument);
+				}
 				if (self::isUninformativeSendTarget($declaredArgument)) {
 					// An unresolved call parameter, like mixed, uses the object without
 					// constraining it. Return/property templates are fixed by their

diff --git a/tests/PHPStan/Rules/Classes/InstantiationRuleTest.php b/tests/PHPStan/Rules/Classes/InstantiationRuleTest.php
@@ -76,6 +76,16 @@ public function testTemplateArgumentArrow(): void
 		$this->analyse([__DIR__ . '/data/template-argument-arrow.php'], []);
 	}
 
+	public function testTemplateArgumentNestedCollection(): void
+	{
+		$this->analyse([__DIR__ . '/data/template-argument-nested-collection.php'], [
+			[
+				'Parameter #1 $events of class TemplateArgumentNestedCollection\ContainerEvent constructor expects TemplateArgumentNestedCollection\EventCollection<TemplateArgumentNestedCollection\WrittenEvent<ID of array<string, string>|string = string>>, TemplateArgumentNestedCollection\EventCollection<TemplateArgumentNestedCollection\Event> given.',
+				62,
+			],
+		]);
+	}
+
 	public function testInstantiation(): void
 	{
 		$this->analyse(

diff --git a/tests/PHPStan/Rules/Classes/data/template-argument-nested-collection.php b/tests/PHPStan/Rules/Classes/data/template-argument-nested-collection.php
@@ -0,0 +1,63 @@
+<?php
+
+namespace TemplateArgumentNestedCollection;
+
+class Event
+{
+}
+
+/** @template T */
+class Collection
+{
+
+	/** @param iterable<T> $items */
+	public function __construct(iterable $items = [])
+	{
+	}
+
+}
+
+/**
+ * @template T of Event = Event
+ * @extends Collection<T>
+ */
+class EventCollection extends Collection
+{
+}
+
+/** @template ID of string|array<string, string> = string */
+class WrittenEvent extends Event
+{
+
+	/** @param ID $id */
+	public function __construct($id)
+	{
+	}
+
+}
+
+/** @template ID of string|array<string, string> = string */
+class ContainerEvent
+{
+
+	/** @param EventCollection<WrittenEvent<ID>> $events */
+	public function __construct(EventCollection $events)
+	{
+	}
+
+}
+
+function emptyCollection(): void
+{
+	new ContainerEvent(new EventCollection());
+}
+
+function populatedCollection(): void
+{
+	new ContainerEvent(new EventCollection([new WrittenEvent('foo')]));
+}
+
+function incompatibleCollection(): void
+{
+	new ContainerEvent(new EventCollection([new Event()]));
+}