mirror: keep updating when only `typenames` remain (#1765)

Summary:
This fixes a bug introduced in #1665, where we added a `typenames`
clause to the query plan but didn’t update the termination checking
accordingly. As a result, query plans with only `typenames` left to
update would not execute, so `extract` would fail with a `NOT NULL`
constraint violation because not all transitively needed objects had
been fetched.

Databases created before this change are still valid. Re-running the
problematic `sourcecred load` command should successfully update the
cache and proceed.

Fixes #1762.

Test Plan:
Regression test added; `aracred/ideas` and `aracred/aracred-template`
both load successfully now.

wchargin-branch: mirror-typenames-only-plan

src/graphql/mirror.js

@@ -645,6 +645,18 @@ export class Mirror {
     });
   }
 
+  /**
+   * Check whether the given query plan indicates that the mirror is
+   * already up to date and no further queries are required.
+   */
+  _isUpToDate(queryPlan: QueryPlan): boolean {
+    return (
+      queryPlan.typenames.length === 0 &&
+      queryPlan.objects.length === 0 &&
+      queryPlan.connections.length === 0
+    );
+  }
+
   /**
    * Create a GraphQL selection set to fetch data corresponding to the
    * given query plan.
@@ -948,7 +960,7 @@ export class Mirror {
     |}
   ): Promise<boolean> {
     const queryPlan = this._findOutdated(options.since);
-    if (queryPlan.objects.length === 0 && queryPlan.connections.length === 0) {
+    if (this._isUpToDate(queryPlan)) {
       return Promise.resolve(false);
     }
     const querySelections = this._queryFromPlan(queryPlan, {

src/graphql/mirror.test.js

@@ -636,6 +636,52 @@ describe("graphql/mirror", () => {
       });
     });
 
+    describe("_isUpToDate", () => {
+      it("marks empty query plans as up to date", () => {
+        const db = new Database(":memory:");
+        const mirror = new Mirror(db, buildGithubSchema());
+        expect(
+          mirror._isUpToDate({typenames: [], objects: [], connections: []})
+        ).toBe(true);
+      });
+      it("marks query plans with typename queries as dirty", () => {
+        const db = new Database(":memory:");
+        const mirror = new Mirror(db, buildGithubSchema());
+        expect(
+          mirror._isUpToDate({typenames: ["foo"], objects: [], connections: []})
+        ).toBe(false);
+      });
+      it("marks query plans with object queries as dirty", () => {
+        const db = new Database(":memory:");
+        const mirror = new Mirror(db, buildGithubSchema());
+        expect(
+          mirror._isUpToDate({
+            typenames: [],
+            objects: [{typename: "Repository", id: "bar"}],
+            connections: [],
+          })
+        ).toBe(false);
+      });
+      it("marks query plans with connection queries as dirty", () => {
+        const db = new Database(":memory:");
+        const mirror = new Mirror(db, buildGithubSchema());
+        expect(
+          mirror._isUpToDate({
+            typenames: [],
+            objects: [],
+            connections: [
+              {
+                objectTypename: "Issue",
+                objectId: "baz",
+                fieldname: "comments",
+                endCursor: undefined,
+              },
+            ],
+          })
+        ).toBe(false);
+      });
+    });
+
     describe("_queryFromPlan", () => {
       it("errors if connections for an object have distinct typename", () => {
         const db = new Database(":memory:");