Add tests for duplicate/indirect trait use and fix false positive

When a class uses the same trait multiple times (directly or indirectly
through another trait), PHP does not consider it a collision. Track the
original declaring trait to avoid false positives in cross-trait method
collision detection.

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

Author: phpstan-bot

src/Rules/Classes/DuplicateDeclarationHelper.php

@@ -13,6 +13,7 @@
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\ShouldNotHappenException;
 use function array_key_exists;
+use function array_values;
 use function count;
 use function is_string;
 use function sprintf;
@@ -155,7 +156,7 @@ public static function checkTraitMethodCollisions(ClassLike $classLike, ClassRef
 		}
 
 		// Collect methods from each trait
-		/** @var array<string, list<array{string, string}>> $methodTraits methodNameLower => [[traitDisplayName, originalMethodName], ...] */
+		/** @var array<string, array<string, array{string, string}>> $methodTraits methodNameLower => [originTraitName => [traitDisplayName, originalMethodName]] */
 		$methodTraits = [];
 		$traits = $classReflection->getTraits();
 		foreach ($traits as $trait) {
@@ -173,7 +174,16 @@ public static function checkTraitMethodCollisions(ClassLike $classLike, ClassRef
 					continue;
 				}
 
-				$methodTraits[$methodNameLower][] = [$trait->getDisplayName(), $method->getName()];
+				// Find the original declaring trait to avoid false positives
+				// when the same method reaches a class through multiple trait paths
+				$originTrait = self::findOriginalDeclaringTrait($trait, $methodNameLower);
+				$originKey = strtolower($originTrait->getName());
+
+				// Only record one entry per origin trait - if the same method
+				// reaches the class from the same origin via different paths, it's not a collision
+				if (!array_key_exists($methodNameLower, $methodTraits) || !array_key_exists($originKey, $methodTraits[$methodNameLower])) {
+					$methodTraits[$methodNameLower][$originKey] = [$trait->getDisplayName(), $method->getName()];
+				}
 			}
 		}
 
@@ -187,14 +197,15 @@ public static function checkTraitMethodCollisions(ClassLike $classLike, ClassRef
 		}
 
 		// Report conflicts
-		foreach ($methodTraits as $traitInfos) {
-			if (count($traitInfos) <= 1) {
+		foreach ($methodTraits as $originInfos) {
+			$infos = array_values($originInfos);
+			if (count($infos) <= 1) {
 				continue;
 			}
 
 			$errors[] = RuleErrorBuilder::message(sprintf(
 				'Trait method %s has not been applied, because there are collisions with other trait methods on %s.',
-				$traitInfos[1][0] . '::' . $traitInfos[1][1] . '()',
+				$infos[1][0] . '::' . $infos[1][1] . '()',
 				$classReflection->getDisplayName(),
 			))->identifier('class.traitMethodCollision')
 				->line($useLine ?? $classLike->getStartLine())
@@ -205,4 +216,15 @@ public static function checkTraitMethodCollisions(ClassLike $classLike, ClassRef
 		return $errors;
 	}
 
+	private static function findOriginalDeclaringTrait(ClassReflection $traitReflection, string $methodNameLower): ClassReflection
+	{
+		foreach ($traitReflection->getTraits() as $subTrait) {
+			if ($subTrait->hasMethod($methodNameLower)) {
+				return self::findOriginalDeclaringTrait($subTrait, $methodNameLower);
+			}
+		}
+
+		return $traitReflection;
+	}
+
 }

tests/PHPStan/Rules/Classes/data/trait-method-collisions.php

@@ -116,3 +116,27 @@ class AliasedTalker
 		TraitF::bigTalk as talk;
 	}
 }
+
+trait TraitG
+{
+	public function doFoo(): void {}
+}
+
+trait TraitH
+{
+	use TraitG;
+}
+
+// Should not report - same trait used twice via separate use statements
+class DuplicateTraitUse
+{
+	use TraitG;
+	use TraitG;
+}
+
+// Should not report - trait used directly and indirectly via another trait
+class IndirectTraitUse
+{
+	use TraitG;
+	use TraitH;
+}