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

@@ -53,11 +53,22 @@ const skippedSDLRules: ValidationRule[] = [
 // Currently, this PossibleTypeExtensions rule is experimental and thus not
 // exposed directly from the rules module above. This may change in the future!
 // Additionally, it does not exist in prior graphql versions. Thus this try/catch.
+//
+// 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@15
   const PossibleTypeExtensions: typeof import("graphql/validation/rules/PossibleTypeExtensions").PossibleTypeExtensions = require("graphql/validation/rules/PossibleTypeExtensions")
     .PossibleTypeExtensions;
+
+  // Compatible for graphql@16
+  const PossibleTypeExtensionsRule = require("graphql")
+    .PossibleTypeExtensionsRule;
+
   if (PossibleTypeExtensions) {
     skippedSDLRules.push(PossibleTypeExtensions);
+  } else 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