[graphql] Add support for printing SchemaExtension nodes (#12519)

* Add support for printing SchemaExtension nodes

* Add changelog entry

* Lint

* Update 12519.md

Co-authored-by: fisker Cheung <lionkay@gmail.com>

changelog_unreleased/graphql/12519.md

@@ -0,0 +1,17 @@
+#### Add support for printing SchemaExtension nodes (#12519 by @trevor-scheer)
+
+<!-- prettier-ignore -->
+```graphql
+# Input
+extend schema { subscription: Subscription }
+extend schema @directive
+
+# Prettier stable
+N/A - throws error
+
+# Prettier main
+extend schema {
+  subscription: Subscription
+}
+extend schema @directive
+```

src/language-graphql/printer-graphql.js

@@ -402,6 +402,29 @@ function genericPrint(path, options, print) {
       ];
     }
 
+    case "SchemaExtension": {
+      return [
+        "extend schema",
+        printDirectives(path, print, node),
+        ...(node.operationTypes.length > 0
+          ? [
+              " {",
+              indent([
+                hardline,
+                join(
+                  hardline,
+                  path.call(
+                    (opsPath) => printSequence(opsPath, options, print),
+                    "operationTypes"
+                  )
+                ),
+              ]),
+              hardline,
+              "}",
+            ]
+          : []),
+      ];
+    }
     case "SchemaDefinition": {
       return [
         print("description"),

tests/format/graphql/kitchen-sink/__snapshots__/jsfmt.spec.js.snap

@@ -149,6 +149,10 @@ schema {
   mutation: MutationType
 }
 
+extend schema @directive {
+  subscription: Subscription
+}
+
 """
 This is a description
 of the \`Foo\` type.
@@ -271,6 +275,10 @@ schema {
   mutation: MutationType
 }
 
+extend schema @directive {
+  subscription: Subscription
+}
+
 """
 This is a description
 of the \`Foo\` type.

tests/format/graphql/kitchen-sink/schema_kitchen_sink.graphql

@@ -8,6 +8,10 @@ schema {
   mutation: MutationType
 }
 
+extend schema @directive {
+  subscription: Subscription
+}
+
 """
 This is a description
 of the `Foo` type.

tests/format/graphql/schema/__snapshots__/jsfmt.spec.js.snap

@@ -13,6 +13,13 @@ schema {
   subscription: Subscription
 }
 
+extend schema { subscription: Subscription }
+
+# \`SchemaExtension\`s don't require any operation types and doesn't print
+# curlies in their abscence.
+extend schema
+  @directive
+
 =====================================output=====================================
 """
 Schema definition description
@@ -23,5 +30,13 @@ schema {
   subscription: Subscription
 }
 
+extend schema {
+  subscription: Subscription
+}
+
+# \`SchemaExtension\`s don't require any operation types and doesn't print
+# curlies in their abscence.
+extend schema @directive
+
 ================================================================================
 `;

tests/format/graphql/schema/schema.graphql

@@ -4,3 +4,10 @@ schema {
   mutation: Mutation
   subscription: Subscription
 }
+
+extend schema { subscription: Subscription }
+
+# `SchemaExtension`s don't require any operation types and doesn't print
+# curlies in their abscence.
+extend schema
+  @directive