mirror: initialize EAV primitives at registration (#1341)

Summary:
This establishes the invariant that every object in the `objects` table
has all relevant rows in the `primitives` table, though those rows’
values are never yet set.

Test Plan:
Unit tests updated. Manually loading `sourcecred/example-github` and
running `.dump primitives` generates reasonable-looking output, with
lots of rows, including entries for nested fields and eggs. Verified
that the set of non-`id` columns on `Issue` equals the set of values for
the `fieldname` column of an `Issue` object, and likewise for `Commit`s,
thus covering each kind of field.

wchargin-branch: mirror-eav-init

src/graphql/mirror.js

@@ -196,7 +196,7 @@ export class Mirror {
     // it requires bumping the version, bump it: requiring some extra
     // one-time cache resets is okay; doing the wrong thing is not.
     const blob = stringify({
-      version: "MIRROR_v4",
+      version: "MIRROR_v5",
       schema: this._schema,
       options: {
         blacklistedIds: this._blacklistedIds,
@@ -479,6 +479,12 @@ export class Mirror {
         `
       )
       .run(id);
+    const addPrimitive = this._db.prepare(
+      dedent`
+        INSERT INTO primitives (object_id, fieldname, value)
+        VALUES (:id, :fieldname, NULL)
+      `
+    );
     const addLink = this._db.prepare(
       dedent`\
         INSERT INTO links (parent_id, fieldname, child_id)
@@ -495,12 +501,20 @@ export class Mirror {
       `
     );
     const objectType = this._schemaInfo.objectTypes[typename];
+    for (const fieldname of objectType.primitiveFieldNames) {
+      addPrimitive.run({id, fieldname});
+    }
     for (const fieldname of objectType.linkFieldNames) {
       addLink.run({id, fieldname});
     }
     for (const parentFieldname of objectType.nestedFieldNames) {
-      const children = objectType.nestedFields[parentFieldname].nodes;
-      for (const childFieldname of Object.keys(children)) {
+      addPrimitive.run({id, fieldname: parentFieldname});
+      const children = objectType.nestedFields[parentFieldname];
+      for (const childFieldname of Object.keys(children.primitives)) {
+        const fieldname = `${parentFieldname}.${childFieldname}`;
+        addPrimitive.run({id, fieldname});
+      }
+      for (const childFieldname of Object.keys(children.nodes)) {
         const fieldname = `${parentFieldname}.${childFieldname}`;
         addLink.run({id, fieldname});
       }

src/graphql/mirror.test.js

@@ -360,6 +360,15 @@ describe("graphql/mirror", () => {
             title: null,
           },
         ]);
+        expect(
+          db
+            .prepare(
+              "SELECT fieldname FROM primitives WHERE object_id = ? " +
+                "ORDER BY fieldname ASC"
+            )
+            .pluck()
+            .all(issueId)
+        ).toEqual(["url", "title"].sort());
 
         expect(
           db
@@ -369,6 +378,12 @@ describe("graphql/mirror", () => {
             .pluck()
             .get()
         ).toBe(0);
+        expect(
+          db
+            .prepare("SELECT COUNT(1) FROM primitives WHERE value IS NOT NULL")
+            .pluck()
+            .get()
+        ).toBe(0);
         expect(
           db
             .prepare("SELECT COUNT(1) FROM links WHERE child_id IS NOT NULL")
@@ -418,6 +433,15 @@ describe("graphql/mirror", () => {
             "author.date": null,
           },
         ]);
+        expect(
+          db
+            .prepare(
+              "SELECT fieldname FROM primitives WHERE object_id = ? " +
+                "ORDER BY fieldname ASC"
+            )
+            .pluck()
+            .all(commitId)
+        ).toEqual(["oid", "author", "author.date"].sort());
 
         expect(
           db