Do not generalize template types in @template-covariant

Author: ondrejmirtes

src/Analyser/MutatingScope.php

@@ -5063,11 +5063,13 @@ private function exactInstantiation(New_ $node, string $className): ?Type
 return $type->getBound();
 }
 
-$isArrayKey = $type->getBound()->describe(VerbosityLevel::precise()) === '(int|string)';
-if ($newType->isScalar()->yes() && !$type->getVariance()->covariant() && $isArrayKey) {
-$newType = $newType->generalize(GeneralizePrecision::templateArgument());
-} elseif ($newType->isConstantValue()->yes() && (!$type->getBound()->isScalar()->yes() || $isArrayKey)) {
-$newType = $newType->generalize(GeneralizePrecision::templateArgument());
+if (!$type->getVariance()->covariant()) {
+$isArrayKey = $type->getBound()->describe(VerbosityLevel::precise()) === '(int|string)';
+if ($newType->isScalar()->yes() && $isArrayKey) {
+$newType = $newType->generalize(GeneralizePrecision::templateArgument());
+} elseif ($newType->isConstantValue()->yes() && (!$type->getBound()->isScalar()->yes() || $isArrayKey)) {
+$newType = $newType->generalize(GeneralizePrecision::templateArgument());
+}
 }
 
 return $newType;

src/Reflection/ResolvedFunctionVariant.php

@@ -184,11 +184,13 @@ private function resolveResolvableTemplateTypes(Type $type, TemplateTypeVariance
 return $traverse($type);
 }
 
-$isArrayKey = $type->getBound()->describe(VerbosityLevel::precise()) === '(int|string)';
-if ($newType->isScalar()->yes() && !$type->getVariance()->covariant() && $isArrayKey) {
-$newType = $newType->generalize(GeneralizePrecision::templateArgument());
-} elseif ($newType->isConstantValue()->yes() && (!$type->getBound()->isScalar()->yes() || $isArrayKey)) {
-$newType = $newType->generalize(GeneralizePrecision::templateArgument());
+if (!$type->getVariance()->covariant()) {
+$isArrayKey = $type->getBound()->describe(VerbosityLevel::precise()) === '(int|string)';
+if ($newType->isScalar()->yes() && $isArrayKey) {
+$newType = $newType->generalize(GeneralizePrecision::templateArgument());
+} elseif ($newType->isConstantValue()->yes() && (!$type->getBound()->isScalar()->yes() || $isArrayKey)) {
+$newType = $newType->generalize(GeneralizePrecision::templateArgument());
+}
 }
 
 $variance = TemplateTypeVariance::createInvariant();

tests/PHPStan/Analyser/data/bug-7078.php

@@ -33,5 +33,5 @@ public function get(TypeDefault ...$type);
 
 function (Param $p) {
 $result = $p->get(new TypeDefault(1), new TypeDefault('a'));
-assertType('int|string', $result);
+assertType('1|\'a\'', $result);
 };

tests/PHPStan/Analyser/data/generics-do-not-generalize.php

@@ -117,3 +117,32 @@ function (): void {
 
 assertType('ArrayIterator<int, string>', createArrayIterator($a));
 };
+
+/** @template T */
+class FooInvariant
+{
+
+/** @param T $p */
+public function __construct($p)
+{
+
+}
+
+}
+
+/** @template-covariant T */
+class FooCovariant
+{
+
+/** @param T $p */
+public function __construct($p)
+{
+
+}
+
+}
+
+function (): void {
+assertType('GenericsDoNotGeneralize\\FooInvariant<int>', new FooInvariant(1));
+assertType('GenericsDoNotGeneralize\\FooCovariant<1>', new FooCovariant(1));
+};