Skip private ctors only when those have zero params (#159)

Author: janedbal

README.md

@@ -328,6 +328,7 @@ parameters:
 
 #### Private constructors:
 - Those are never reported as dead as those are often used to deny class instantiation
+  - This applies only to constructors without any parameters
 
 #### Interface methods:
 - If you never call interface method over the interface, but only over its implementors, it gets reported as dead

src/Collector/ClassDefinitionCollector.php

@@ -19,13 +19,14 @@
 use ShipMonk\PHPStan\DeadCode\Enum\Visibility;
 use function array_fill_keys;
 use function array_map;
+use function count;
 
 /**
  * @implements Collector<ClassLike, array{
  *       kind: string,
  *       name: string,
  *       constants: array<string, array{line: int}>,
- *       methods: array<string, array{line: int, abstract: bool, visibility: int-mask-of<Visibility::*>}>,
+ *       methods: array<string, array{line: int, params: int, abstract: bool, visibility: int-mask-of<Visibility::*>}>,
  *       parents: array<string, null>,
  *       traits: array<string, array{excluded?: list<string>, aliases?: array<string, string>}>,
  *       interfaces: array<string, null>,
@@ -52,7 +53,7 @@ public function getNodeType(): string
      *      kind: string,
      *      name: string,
      *      constants: array<string, array{line: int}>,
-     *      methods: array<string, array{line: int, abstract: bool, visibility: int-mask-of<Visibility::*>}>,
+     *      methods: array<string, array{line: int, params: int, abstract: bool, visibility: int-mask-of<Visibility::*>}>,
      *      parents: array<string, null>,
      *      traits: array<string, array{excluded?: list<string>, aliases?: array<string, string>}>,
      *      interfaces: array<string, null>,
@@ -76,6 +77,7 @@ public function processNode(
         foreach ($node->getMethods() as $method) {
             $methods[$method->name->toString()] = [
                 'line' => $method->getStartLine(),
+                'params' => count($method->params),
                 'abstract' => $method->isAbstract() || $node instanceof Interface_,
                 'visibility' => $method->flags & (Visibility::PUBLIC | Visibility::PROTECTED | Visibility::PRIVATE),
             ];

src/Rule/DeadCodeRule.php

@@ -76,7 +76,7 @@ class DeadCodeRule implements Rule, DiagnoseExtension
      *      name: string,
      *      file: string,
      *      constants: array<string, array{line: int}>,
-     *      methods: array<string, array{line: int, abstract: bool, visibility: int-mask-of<Visibility::*>}>,
+     *      methods: array<string, array{line: int, params: int, abstract: bool, visibility: int-mask-of<Visibility::*>}>,
      *      parents: array<string, null>,
      *      traits: array<string, array{excluded?: list<string>, aliases?: array<string, string>}>,
      *      interfaces: array<string, null>
@@ -692,6 +692,7 @@ private function isNeverReportedAsDead(BlackMember $blackMember): bool
         }
 
         $kind = $this->typeDefinitions[$typeName]['kind'] ?? null;
+        $params = $this->typeDefinitions[$typeName]['methods'][$memberName]['params'] ?? 0;
         $abstract = $this->typeDefinitions[$typeName]['methods'][$memberName]['abstract'] ?? false;
         $visibility = $this->typeDefinitions[$typeName]['methods'][$memberName]['visibility'] ?? 0;
 
@@ -701,8 +702,8 @@ private function isNeverReportedAsDead(BlackMember $blackMember): bool
             return true;
         }
 
-        if ($memberName === '__construct' && ($visibility & Visibility::PRIVATE) !== 0) {
-            // private constructors are often used to deny instantiation
+        if ($memberName === '__construct' && ($visibility & Visibility::PRIVATE) !== 0 && $params === 0) {
+            // private constructors with zero parameters are often used to deny instantiation
             return true;
         }
 

tests/Rule/data/methods/ctor-denied.php

@@ -9,3 +9,12 @@ private function __construct()
     }
 }
 
+class NotUtility
+{
+    private function __construct(private int $foo) // error: Unused CtorDenied\NotUtility::__construct
+    {
+
+    }
+
+}
+