Add compatible logic for graphql@16

Author: m1heng

packages/apollo-graphql/package.json

@@ -16,7 +16,7 @@
     "sha.js": "^2.4.11"
   },
   "peerDependencies": {
-    "graphql": "^14.2.1 || ^15.0.0"
+    "graphql": "^14.2.1 || ^15.0.0 || ^16.0.0"
   },
   "jest": {
     "preset": "ts-jest",

packages/apollo-graphql/src/schema/buildSchemaFromSDL.ts

@@ -56,6 +56,7 @@ const skippedSDLRules: ValidationRule[] = [
 try {
   const PossibleTypeExtensions: typeof import("graphql/validation/rules/PossibleTypeExtensions").PossibleTypeExtensions = require("graphql/validation/rules/PossibleTypeExtensions")
     .PossibleTypeExtensions;
+
   if (PossibleTypeExtensions) {
     skippedSDLRules.push(PossibleTypeExtensions);
   }
@@ -64,6 +65,21 @@ try {
   // by the version of `graphql` that is available to us.
 }
 
+// BREAKING AGAIN: PossibleTypeExtensions is finilized into PossibleTypeExtensionsRule in
+// graphql 16. For compatible reason, try catch logic for 15 is kept with extra logic for 16.
+try {
+  // Compatible for graphql-js@16
+  const PossibleTypeExtensionsRule = require("graphql")
+    .PossibleTypeExtensionsRule;
+
+  if (PossibleTypeExtensionsRule) {
+    skippedSDLRules.push(PossibleTypeExtensionsRule);
+  }
+} catch (e) {
+  // No need to fail in this case.  Instead, if this validation rule is missing, we will assume its not used
+  // by the version of `graphql` that is available to us.
+}
+
 const sdlRules = specifiedSDLRules.filter(
   rule => !skippedSDLRules.includes(rule)
 );