mirror: add typename support to `UpdateResult`s (#1664)

Summary:
The internal `UpdateResult` structure now lists IDs of objects whose
typename has been queried. This list is expected to be empty for now.

Test Plan:
Unit tests added.

wchargin-branch: mirror-typename-updateresult

src/graphql/mirror.js

@@ -735,7 +735,9 @@ export class Mirror {
     queryResult: UpdateResult
   ): void {
     for (const topLevelKey of Object.keys(queryResult)) {
-      if (topLevelKey.startsWith(_FIELD_PREFIXES.OWN_DATA)) {
+      if (topLevelKey.startsWith(_FIELD_PREFIXES.TYPENAMES)) {
+        throw new Error("Typename update results not yet supported");
+      } else if (topLevelKey.startsWith(_FIELD_PREFIXES.OWN_DATA)) {
         const rawValue: OwnDataUpdateResult | NodeConnectionsUpdateResult =
           queryResult[topLevelKey];
         const updateRecord: OwnDataUpdateResult = (rawValue: any);
@@ -2092,6 +2094,16 @@ type NestedFieldResult = {
   +[Schema.Fieldname]: PrimitiveResult | NodeFieldResult,
 } | null;
 
+/**
+ * Result describing only the typename of a set of nodes. Used when we
+ * only have references to nodes via unfaithful fields.
+ */
+type TypenamesUpdateResult = $ReadOnlyArray<{|
+  +__typename: Schema.Typename,
+  +id: Schema.ObjectId,
+|}>;
+export type _TypenamesUpdateResult = TypenamesUpdateResult; // for tests
+
 /**
  * Result describing own-data for many nodes of a given type. Whether a
  * value is a `PrimitiveResult` or a `NodeFieldResult` is determined by
@@ -2107,6 +2119,7 @@ type OwnDataUpdateResult = $ReadOnlyArray<{
     | NodeFieldResult
     | NestedFieldResult,
 }>;
+export type _OwnDataUpdateResult = OwnDataUpdateResult; // for tests
 
 /**
  * Result describing new elements for connections on a single node.
@@ -2117,12 +2130,13 @@ type NodeConnectionsUpdateResult = {
   +id: Schema.ObjectId,
   +[connectionFieldname: Schema.Fieldname]: ConnectionFieldResult,
 };
+export type _NodeConnectionsUpdateResult = NodeConnectionsUpdateResult; // for tests
 
 /**
- * Result describing both own-data updates and connection updates. Each
+ * Result describing all kinds of updates. Each key's prefix determines
- * key's prefix determines what type of results the corresponding value
+ * what type of results the corresponding value represents (see
- * represents (see constants below). No field prefix is a prefix of
+ * constants below). No field prefix is a prefix of another, so this
- * another, so this characterization is complete.
+ * characterization is complete.
  *
  * This type would be exact but for facebook/flow#2977, et al.
  *
@@ -2131,10 +2145,19 @@ type NodeConnectionsUpdateResult = {
 type UpdateResult = {
   // The prefix of each key determines what type of results the value
   // represents. See constants below.
-  +[string]: OwnDataUpdateResult | NodeConnectionsUpdateResult,
+  +[string]:
+    | TypenamesUpdateResult
+    | OwnDataUpdateResult
+    | NodeConnectionsUpdateResult,
 };
 
 export const _FIELD_PREFIXES = deepFreeze({
+  /**
+   * A key of an `UpdateResult` has this prefix if and only if the
+   * corresponding value represents `TypenamesUpdateResult`s.
+   */
+  TYPENAMES: "typenames_",
+
   /**
    * A key of an `UpdateResult` has this prefix if and only if the
    * corresponding value represents `OwnDataUpdateResult`s.

src/graphql/mirror.test.js

@@ -13,6 +13,8 @@ import {
   _inTransaction,
   _makeSingleUpdateFunction,
   Mirror,
+  type _OwnDataUpdateResult,
+  type _TypenamesUpdateResult,
 } from "./mirror";
 import stringify from "json-stable-stringify";
 
@@ -799,6 +801,20 @@ describe("graphql/mirror", () => {
         }).toThrow('Bad key in query result: "wat_0"');
       });
 
+      it("throws if given a key with typename results", () => {
+        const db = new Database(":memory:");
+        const mirror = new Mirror(db, buildGithubSchema());
+        const updateId = mirror._createUpdate(new Date(123));
+        const result = {
+          typenames_0: ([
+            {id: "issue:#1", __typename: "Issue"},
+          ]: _TypenamesUpdateResult),
+        };
+        expect(() => {
+          mirror._nontransactionallyUpdateData(updateId, result);
+        }).toThrow("Typename update results not yet supported");
+      });
+
       // We test the happy path lightly, because it just delegates to
       // other methods, which are themselves tested. This test is
       // sufficient to effect full coverage.
@@ -810,14 +826,14 @@ describe("graphql/mirror", () => {
         mirror.registerObject({typename: "Issue", id: "issue:#1"});
         mirror.registerObject({typename: "Issue", id: "issue:#2"});
         const result = {
-          owndata_0: [
+          owndata_0: ([
             {
               __typename: "Repository",
               id: "repo:foo/bar",
               url: "url://foo/bar",
             },
-          ],
+          ]: _OwnDataUpdateResult),
-          owndata_1: [
+          owndata_1: ([
             {
               __typename: "Issue",
               id: "issue:#1",
@@ -846,7 +862,7 @@ describe("graphql/mirror", () => {
                 id: "user:alice",
               },
             },
-          ],
+          ]: _OwnDataUpdateResult),
           node_0: {
             id: "repo:foo/bar",
             issues: {
@@ -3797,13 +3813,13 @@ describe("graphql/mirror", () => {
         const rowid = mirror._logRequest(query, queryParameters, new Date(123));
 
         const response = {
-          owndata_0: [
+          owndata_0: ([
             {
               __typename: "Repository",
               id: "repo:foo/bar",
               url: "url://foo/bar",
             },
-          ],
+          ]: _OwnDataUpdateResult),
         };
 
         mirror._logResponse(rowid, response, new Date(456));