ForbidVariableTypeOverwritingRule: fix false positive with fluent $this returns (#347)

Generalize StaticType to its base ObjectType before comparison, so that
methods returning $this/static don't cause false positives when reassigning
to the same variable. Keep isSuperTypeOf() for comparison to preserve
detection of int/float type changes.

Author: janedbal

src/Rule/ForbidVariableTypeOverwritingRule.php

@@ -16,6 +16,7 @@
 use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\MixedType;
+use PHPStan\Type\StaticType;
 use PHPStan\Type\SubtractableType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
@@ -63,10 +64,10 @@ public function processNode(
             return [];
         }
 
-        $narrowing = $previousVariableType->accepts($newVariableType, true)->yes();
-        $generalization = $newVariableType->accepts($previousVariableType, true)->yes();
-
-        if (!$narrowing && !$generalization) {
+        if (
+            !$previousVariableType->isSuperTypeOf($newVariableType)->yes() // allow narrowing
+            && !$newVariableType->isSuperTypeOf($previousVariableType)->yes() // allow generalization
+        ) {
             $error = RuleErrorBuilder::message("Overwriting variable \$$variableName while changing its type from {$previousVariableType->describe(VerbosityLevel::precise())} to {$newVariableType->describe(VerbosityLevel::precise())}")
                 ->identifier('shipmonk.variableTypeOverwritten')
                 ->build();
@@ -85,6 +86,10 @@ private function generalizeDeeply(Type $type): Type
 
     private function generalize(Type $type): Type
     {
+        if ($type instanceof StaticType) {
+            $type = $type->getStaticObjectType(); // @phpstan-ignore shipmonk.variableTypeOverwritten
+        }
+
         if (
             $type->isConstantValue()->yes()
             || $type instanceof IntegerRangeType

tests/Rule/data/ForbidVariableTypeOverwritingRule/code.php

@@ -163,6 +163,14 @@ function testIntToInt(int $positive, int $negative) {
     $positive = $negative;
 }
 
+function testFloatToInt(float $float, int $int) {
+    $float = $int; // error: Overwriting variable $float while changing its type from float to int
+}
+
+function testIntToFloat(int $int, float $float) {
+    $int = $float; // error: Overwriting variable $int while changing its type from int to float
+}
+
 class FluentClass {
     /** @return $this */
     public function orderBy(): static {