(core) add missing tsconfig file that affects IDEs

Summary:
I missed committing a file that is important for editing files comfortably in the ext directory in an IDE. This diff:

 * Adds tsconfig-base-ext.json - that was the only intended change
 * Unrelated: Forces all creation of connections to the home db through a new `getOrCreateConnection` method which changes the `busy_timeout` if using Sqlite. This was an attempt to fix random "database is locked" test failures. I believe multiple connections to the home db as an sqlite file do not happen in self-hosted Grist (where there is a single node process) or in our SaaS (where the database is in postgres). It does affect Grist started using `devServerMain.ts` (where multiple processes accessing same database are started) or various test configurations when extra database connections are opened.
 * Unrelated: I added a `busy_timeout` for session storage, when it uses Sqlite. Again, I don't believe this affects self-hosted Grist or our SaaS.
 * Tweaked a `BillingDiscount` test that looked perhaps vulnerable to a stripe request stalling.

I can't be sure my tweaks actually help, since I didn't succeed in replicating the failures. Update: looks like the "locked" error can still happen :(

Test Plan: manual

Reviewers: jarek

Reviewed By: jarek

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3450

app/gen-server/lib/HomeDBManager.ts

@@ -50,6 +50,7 @@ import {
   now,
   readJson
 } from 'app/gen-server/sqlUtils';
+import {getOrCreateConnection} from 'app/server/lib/dbUtils';
 import {makeId} from 'app/server/lib/idUtils';
 import * as log from 'app/server/lib/log';
 import {Permit} from 'app/server/lib/Permit';
@@ -60,10 +61,8 @@ import {Request} from "express";
 import {
   Brackets,
   Connection,
-  createConnection,
   DatabaseType,
   EntityManager,
-  getConnection,
   SelectQueryBuilder,
   WhereExpression
 } from "typeorm";
@@ -345,14 +344,7 @@ export class HomeDBManager extends EventEmitter {
   }
 
   public async connect(): Promise<void> {
-    try {
-      // If multiple servers are started within the same process, we
-      // share the database connection.  This saves locking trouble
-      // with Sqlite.
-      this._connection = getConnection();
-    } catch (e) {
-      this._connection = await createConnection();
-    }
+    this._connection = await getOrCreateConnection();
     this._dbType = this._connection.driver.options.type;
   }
 

app/server/lib/dbUtils.ts

@@ -1,5 +1,6 @@
 import {synchronizeProducts} from 'app/gen-server/entity/Product';
-import {Connection, createConnection} from 'typeorm';
+import {Mutex} from 'async-mutex';
+import {Connection, createConnection, getConnection} from 'typeorm';
 
 // Summary of migrations found in database and in code.
 interface MigrationSummary {
@@ -38,11 +39,39 @@ export async function getMigrations(connection: Connection): Promise<MigrationSu
  * Run any needed migrations, and make sure products are up to date.
  */
 export async function updateDb(connection?: Connection) {
-  connection = connection || await createConnection();
+  connection = connection || await getOrCreateConnection();
   await runMigrations(connection);
   await synchronizeProducts(connection, true);
 }
 
+/**
+ * Get a connection to db if one exists, or create one. Serialized to
+ * avoid duplication.
+ */
+const connectionMutex = new Mutex();
+export async function getOrCreateConnection(): Promise<Connection> {
+  return connectionMutex.runExclusive(async() => {
+    try {
+      // If multiple servers are started within the same process, we
+      // share the database connection.  This saves locking trouble
+      // with Sqlite.
+      return getConnection();
+    } catch (e) {
+      const connection = await createConnection();
+      // When using Sqlite, set a busy timeout of 3s to tolerate a little
+      // interference from connections made by tests. Logging doesn't show
+      // any particularly slow queries, but bad luck is possible.
+      // This doesn't affect when Postgres is in use. It also doesn't have
+      // any impact when there is a single connection to the db, as is the
+      // case when Grist is run as a single process.
+      if (connection.driver.options.type === 'sqlite') {
+        await connection.query('PRAGMA busy_timeout = 3000');
+      }
+      return connection;
+    }
+  });
+}
+
 export async function runMigrations(connection: Connection) {
   // on SQLite, migrations fail if we don't temporarily disable foreign key
   // constraint checking.  This is because for sqlite typeorm copies each

app/server/lib/gristSessions.ts

@@ -73,8 +73,16 @@ function createSessionStoreFactory(sessionsDB: string): () => SessionStore {
       const store = new SQLiteStore({
         dir: path.dirname(sessionsDB),
         db: path.basename(sessionsDB),    // SQLiteStore no longer appends a .db suffix.
-        table: 'sessions'
+        table: 'sessions',
       });
+      // In testing, and monorepo's "yarn start", session is accessed from multiple
+      // processes, so could hit lock failures.
+      // connect-sqlite3 has a concurrentDb: true flag that can be set, but
+      // it puts the database in WAL mode, which would have implications
+      // for self-hosters (a second file to think about). Instead we just
+      // set a busy timeout.
+      store.db.run('PRAGMA busy_timeout = 1000');
+
       return assignIn(store, { async close() {}});
     };
   }