Fixed #1294: Inconsistent variance in generics

spec/compiler/codegen/is_a_spec.cr

@@ -602,4 +602,22 @@ describe "Codegen: is_a?" do
       Foo(Int32).is_a?(Foo.class)
       )).to_b.should be_true
   end
+
+  it "says false for GenericChild(Base).is_a?(GenericBase(Child)) (#1294)" do
+    run(%(
+      class Base
+      end
+
+      class Child < Base
+      end
+
+      class GenericBase(T)
+      end
+
+      class GenericChild(T) < GenericBase(T)
+      end
+
+      GenericChild(Base).new.is_a?(GenericBase(Child))
+      )).to_b.should be_false
+  end
 end

spec/compiler/type_inference/restrictions_spec.cr

@@ -234,4 +234,26 @@ describe "Restrictions" do
             (types["Foo"] as GenericClassType).instantiate([float64] of TypeVar),
            ) }
   end
+
+  it "should not let GenericChild(Base) pass as a GenericBase(Child) (#1294)" do
+    assert_error %(
+      class Base
+      end
+
+      class Child < Base
+      end
+
+      class GenericBase(T)
+      end
+
+      class GenericChild(T) < GenericBase(T)
+      end
+
+      def foo(x : GenericBase(Child))
+      end
+
+      foo GenericChild(Base).new
+      ),
+      "no overload matches"
+  end
 end

src/compiler/crystal/semantic/restrictions.cr

@@ -457,7 +457,8 @@ module Crystal
 
       mapping.each do |name, node|
         typevar_type = TypeLookup.lookup(extending_class, node)
-        unless other.type_vars[name].type.is_restriction_of?(typevar_type, owner)
+        other_type = other.type_vars[name].type.devirtualize
+        unless typevar_type.implements?(other_type)
           return nil
         end
       end
@@ -480,7 +481,7 @@ module Crystal
         if m = @mapping[class_type_var]?
           t = TypeLookup.lookup(extending_class, m)
           restricted = t.restrict other_type_var, context
-          return nil unless restricted
+          return nil unless restricted && t == restricted
 
           if other_type_var.is_a?(Path) && other_type_var.names.length == 1
             context.set_free_var(other_type_var.names.first, restricted)