feat(compiler): allow SDL to contain built-in type redefinition

Updates `SchemaBuilder` to allow SDL to contain built-in meta types (e.g. `__Type`) redefinitions. GraphQL spec doesn't really define the expected behavior for handling SDL with redeclared meta fields (see: [#1036](graphql/graphql-spec#1036), [#1049](graphql/graphql-spec#1049)). `graphql-js` [reference implementation](https://github.com/graphql/graphql-js/blob/v16.11.0/src/utilities/extendSchema.ts#L187) simply ignores those redefinitions even if the underlying type definitions don't match.

This PR updates `ignore_builtin_redefinitions` option to also ignore meta types redefinitions (previously it was only allowing built-in scalar redefinitions #990).

Author: dariuszkuc

crates/apollo-compiler/src/schema/from_ast.rs

@@ -134,15 +134,15 @@ impl SchemaBuilder {
                         }
                         Entry::Occupied(entry) => {
                             let previous = entry.get();
+                            if self.ignore_builtin_redefinitions && previous.is_built_in() {
+                                continue;
+                            }
+
                             if $is_scalar && previous.is_built_in() {
-                                if self.ignore_builtin_redefinitions {
-                                    continue;
-                                } else {
-                                    self.errors.push(
-                                        $def.location(),
-                                        BuildError::BuiltInScalarTypeRedefinition,
-                                    )
-                                }
+                                self.errors.push(
+                                    $def.location(),
+                                    BuildError::BuiltInScalarTypeRedefinition,
+                                )
                             } else {
                                 self.errors.push(
                                     $def.name.location(),

crates/apollo-compiler/tests/validation/types.rs

@@ -2020,7 +2020,7 @@ mod variable_default_values {
 }
 
 #[test]
-fn handles_built_in_type_redefinition() {
+fn handles_built_in_scalar_redefinition() {
     let schema = r#"
 scalar String
 
@@ -2049,3 +2049,48 @@ type Query {
         .build()
         .expect("schema parsed successfully");
 }
+
+#[test]
+fn handles_built_in_type_redefinition() {
+    let schema = r#"
+type __Directive {
+  name: String!
+  description: String!
+  isRepeatable: String!
+  args: __InputValue
+  locations: String!
+}
+
+type Query {
+  foo: String
+}
+"#;
+
+    let errors = Schema::parse_and_validate(schema, "schema.graphql")
+        .expect_err("invalid schema")
+        .errors;
+    let expected = expect![[r#"
+        Error: the type `__Directive` is defined multiple times in the schema
+            ╭─[ built_in.graphql:87:6 ]
+            │
+         87 │ type __Directive {
+            │      ─────┬─────  
+            │           ╰─────── previous definition of `__Directive` here
+            │
+            ├─[ schema.graphql:2:6 ]
+            │
+          2 │ type __Directive {
+            │      ─────┬─────  
+            │           ╰─────── `__Directive` redefined here
+            │ 
+            │ Help: remove or rename one of the definitions, or use `extend`
+        ────╯
+    "#]];
+    expected.assert_eq(&errors.to_string());
+
+    let builder = SchemaBuilder::new().ignore_builtin_redefinitions();
+    let _ = builder
+        .parse(schema, "schema.graphql")
+        .build()
+        .expect("schema parsed successfully");
+}