Fix support for Flow's DeclareClass type parameters (#9459)

packages/babel-types/src/definitions/flow.js

@@ -72,7 +72,7 @@ defineType("ClassImplements", {
   },
 });
 
-defineInterfaceishType("DeclareClass", "TypeParameterInstantiation");
+defineInterfaceishType("DeclareClass");
 
 defineType("DeclareFunction", {
   visitor: ["id"],

packages/babel-types/test/builders/flow/declareClass.js

@@ -0,0 +1,32 @@
+import * as t from "../../..";
+
+describe("builders", function() {
+  describe("flow", function() {
+    describe("declareClass", function() {
+      it("accept TypeParameterDeclaration as typeParameters", function() {
+        const typeParameter = t.typeParameter(null, null, null);
+        typeParameter.name = "T";
+        const declaredClass = t.declareClass(
+          t.identifier("A"),
+          t.typeParameterDeclaration([typeParameter]),
+          [],
+          t.objectTypeAnnotation([], [], [], []),
+        );
+        expect(t.isDeclareClass(declaredClass)).toBe(true);
+      });
+
+      it("not accept typeParameterInstantiation as typeParameters", function() {
+        expect(() =>
+          t.declareClass(
+            t.identifier("A"),
+            t.typeParameterInstantiation([
+              t.genericTypeAnnotation(t.identifier("T")),
+            ]),
+            [],
+            t.objectTypeAnnotation([], [], [], []),
+          ),
+        ).toThrow(Error);
+      });
+    });
+  });
+});