Compiler and interpreter: fix is_a? from virtual metaclass to generic…

… metaclass (#12306)

* Compiler: fix `is_a?` from virtual metaclass to generic metaclass

* Interpreter: add missing casts between virtual metaclass and generic metaclass

spec/compiler/interpreter/types_spec.cr

@@ -38,6 +38,25 @@ describe Crystal::Repl::Interpreter do
         CODE
     end
 
+    it "does class method on virtual metaclass casted to generic metaclass (#12302)" do
+      interpret(<<-CODE).should eq(42)
+        class A
+          def self.foo
+            1
+          end
+        end
+
+        class B(T) < A
+          def self.foo
+            42
+          end
+        end
+
+        b = B(String).new.as(A)
+        b.class.foo
+      CODE
+    end
+
     it "discards class for virtual_type type" do
       interpret(<<-CODE).should eq(2)
           class Foo; end

spec/compiler/semantic/is_a_spec.cr

@@ -240,4 +240,22 @@ describe "Semantic: is_a?" do
       end
       ))
   end
+
+  it "does is_a? from virtual metaclass to generic metaclass (#12302)" do
+    assert_type(%(
+      class A
+      end
+
+      class B(T) < A
+      end
+
+      x = B(String).new.as(A).class
+
+      if x.is_a?(B(String).class)
+        x
+      else
+        nil
+      end
+      ), inject_primitives: true) { nilable generic_class("B", string).metaclass }
+  end
 end

src/compiler/crystal/interpreter/cast.cr

@@ -371,11 +371,7 @@ class Crystal::Repl::Compiler
     # Nothing to do
   end
 
-  private def downcast_distinct(node : ASTNode, from : VirtualMetaclassType, to : MetaclassType)
-    # Nothing to do
-  end
-
-  private def downcast_distinct(node : ASTNode, from : VirtualMetaclassType, to : VirtualMetaclassType)
+  private def downcast_distinct(node : ASTNode, from : VirtualMetaclassType, to : MetaclassType | VirtualMetaclassType | GenericClassInstanceMetaclassType | GenericModuleInstanceMetaclassType)
     # Nothing to do
   end
 

src/compiler/crystal/interpreter/compiler.cr

@@ -1734,9 +1734,7 @@ class Crystal::Repl::Compiler < Crystal::Visitor
       end
     when VirtualMetaclassType
       case filtered_type
-      when MetaclassType
-        metaclass_is_a(type_id(filtered_type), node: node)
-      when VirtualMetaclassType
+      when MetaclassType, VirtualMetaclassType, GenericClassInstanceMetaclassType, GenericModuleInstanceMetaclassType
         metaclass_is_a(type_id(filtered_type), node: node)
       else
         node.raise "BUG: missing filter type from #{type} to #{filtered_type} (#{type.class} to #{filtered_type.class})"

src/compiler/crystal/semantic/type_intersect.cr

@@ -97,13 +97,17 @@ module Crystal
       restricted.try(&.metaclass)
     end
 
-    def self.common_descendent(type1 : GenericClassInstanceMetaclassType | GenericModuleInstanceMetaclassType, type2 : MetaclassType)
+    def self.common_descendent(type1 : GenericClassInstanceMetaclassType | GenericModuleInstanceMetaclassType, type2 : MetaclassType | VirtualMetaclassType)
       return type1 if type1.instance_type.generic_type.metaclass == type2
 
       restricted = common_descendent(type1.instance_type, type2.instance_type)
       restricted ? type1 : nil
     end
 
+    def self.common_descendent(type1 : MetaclassType | VirtualMetaclassType, type2 : GenericClassInstanceMetaclassType | GenericModuleInstanceMetaclassType)
+      common_descendent(type2, type1)
+    end
+
     def self.common_descendent(type1 : UnionType, type2 : Type)
       types = type1.union_types.compact_map do |union_type|
         common_descendent(union_type, type2)