Add `RelationalView.addData` (#442)

Now that we want to implement RelationalView de/serialization, we need a
way to construct one without adding data to it.

Now that we're allowing `addData` to be called explicitly, we also want
to make sure it's idempotent, which necessitated a small change to
reference handling. A new test verifies idempotency.

Test plan: travis

Paired with @wchargin

src/v3/plugins/github/example/example.js

@@ -11,7 +11,9 @@ export function exampleData(): GithubResponseJSON {
 }
 
 export function exampleRelationalView(): RelationalView {
-  return new RelationalView(exampleData());
+  const rv = new RelationalView();
+  rv.addData(exampleData());
+  return rv;
 }
 
 export function exampleGraph(): Graph {

src/v3/plugins/github/relationalView.js

@@ -32,7 +32,7 @@ export class RelationalView {
   _mapReferences: Map<N.RawAddress, N.ReferentAddress[]>;
   _mapReferencedBy: Map<N.RawAddress, N.TextContentAddress[]>;
 
-  constructor(data: Q.GithubResponseJSON) {
+  constructor() {
     this._repos = new Map();
     this._issues = new Map();
     this._pulls = new Map();
@@ -41,6 +41,13 @@ export class RelationalView {
     this._userlikes = new Map();
     this._mapReferences = new Map();
     this._mapReferencedBy = new Map();
+  }
+
+  addData(data: Q.GithubResponseJSON) {
+    // Warning: calling `addData` can put the RelationalView in an inconistent
+    // state. for example, if called with {repo: {issues: [1,2,3]}} and then with
+    // {repo: {issues: [4, 5]}}, then calls to repo.issues() will only give back
+    // issues 4 and 5 (although issues 1, 2, and 3 will still be in the view)
     this._addRepo(data.repository);
     this._addReferences();
   }
@@ -281,6 +288,9 @@ export class RelationalView {
   }
 
   _addReferences() {
+    // TODO(perf): _addReferences regenerates all refs from scratch
+    this._mapReferences = new Map();
+    this._mapReferencedBy = new Map();
     // refToAddress maps a "referencing string" to the address that string refers to.
     // There are 3 kinds of valid referencing strings:
     // - A canonical URL pointing to a GitHub entity, e.g.

src/v3/plugins/github/relationalView.test.js

@@ -2,7 +2,7 @@
 
 import * as R from "./relationalView";
 import * as N from "./nodes";
-import {exampleRelationalView} from "./example/example";
+import {exampleData, exampleRelationalView} from "./example/example";
 
 describe("plugins/github/relationalView", () => {
   // Sharing this state is OK because it's just a view - no mutation allowed!
@@ -213,4 +213,14 @@ describe("plugins/github/relationalView", () => {
       expect(nFoundReferences).toEqual(nReferences);
     });
   });
+
+  it("addData is idempotent", () => {
+    const rv1 = new R.RelationalView();
+    rv1.addData(exampleData());
+    const rv2 = new R.RelationalView();
+    rv2.addData(exampleData());
+    rv2.addData(exampleData());
+    // may be fragile
+    expect(rv1).toEqual(rv2);
+  });
 });