mirror: add typename support to query plan (#1663)

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

Test Plan:
Unit tests included.

wchargin-branch: mirror-typename-queryplan

src/graphql/mirror.js

@@ -536,6 +536,9 @@ export class Mirror {
   _findOutdated(since: Date): QueryPlan {
     const db = this._db;
     return _inTransaction(db, () => {
+      // All objects must have recorded typenames due to the `NOT NULL`
+      // constraint on `typename` column of the `objects` table.
+      const typenames: $PropertyType<QueryPlan, "typenames"> = [];
       const objects: $PropertyType<QueryPlan, "objects"> = db
         .prepare(
           dedent`\
@@ -575,7 +578,7 @@ export class Mirror {
           delete result.neverUpdated;
           return result;
         });
-      return {objects, connections};
+      return {typenames, objects, connections};
     });
   }
 
@@ -605,6 +608,9 @@ export class Mirror {
       +connectionPageSize: number,
     |}
   ): Queries.Selection[] {
+    if (queryPlan.typenames.length > 0) {
+      throw new Error("Typename queries not yet supported");
+    }
     // Group objects by type, so that we have to specify each type's
     // fieldset fewer times (only once per `nodesOfTypeLimit` nodes
     // instead of for every node).
@@ -2051,6 +2057,7 @@ type NetworkLogId = number;
  * A set of objects and connections that should be updated.
  */
 type QueryPlan = {|
+  +typenames: $ReadOnlyArray<Schema.ObjectId>,
   +objects: $ReadOnlyArray<{|
     +typename: Schema.Typename,
     +id: Schema.ObjectId,

src/graphql/mirror.test.js

@@ -566,6 +566,7 @@ describe("graphql/mirror", () => {
 
         const actual = mirror._findOutdated(new Date(midUpdate.time));
         const expected = {
+          typenames: [],
           objects: [
             {typename: "Repository", id: "repo:ab/cd"}, // loaded before cutoff
             // issue:ab/cd#1 was loaded after the cutoff
@@ -608,6 +609,7 @@ describe("graphql/mirror", () => {
         const db = new Database(":memory:");
         const mirror = new Mirror(db, buildGithubSchema());
         const plan = {
+          typenames: [],
           objects: [],
           connections: [
             {
@@ -636,10 +638,28 @@ describe("graphql/mirror", () => {
             '"Issue" vs. "Repository"'
         );
       });
+      it("errors if given any typename requests", () => {
+        const db = new Database(":memory:");
+        const mirror = new Mirror(db, buildGithubSchema());
+        const plan = {
+          typenames: ["hmmm"],
+          objects: [],
+          connections: [],
+        };
+        expect(() => {
+          mirror._queryFromPlan(plan, {
+            nodesLimit: 10,
+            nodesOfTypeLimit: 5,
+            connectionLimit: 5,
+            connectionPageSize: 23,
+          });
+        }).toThrow("Typename queries not yet supported");
+      });
       it("creates a good query", () => {
         const db = new Database(":memory:");
         const mirror = new Mirror(db, buildGithubSchema());
         const plan = {
+          typenames: [],
           objects: [
             {typename: "Issue", id: "i#1"},
             {typename: "Repository", id: "repo#2"},
@@ -1136,6 +1156,7 @@ describe("graphql/mirror", () => {
           spyFindOutdated.mock.results[1].value
         );
         expect(spyFindOutdated.mock.results[2].value).toEqual({
+          typenames: [],
           objects: [],
           connections: [],
         });