Attempt to clean up the database cluster directory

This will help to avoid issues where the database cluster directory is left in an inconsistent state.

src/init.test.ts

@@ -1,9 +1,21 @@
+import * as fs from "fs";
+import path from "path";
+
 import test from "ava";
 
 import { Config } from "./config-utils";
-import { printPathFiltersWarning } from "./init";
+import {
+  cleanupDatabaseClusterDirectory,
+  printPathFiltersWarning,
+} from "./init";
 import { Language } from "./languages";
-import { LoggedMessage, getRecordingLogger, setupTests } from "./testing-utils";
+import {
+  LoggedMessage,
+  createTestConfig,
+  getRecordingLogger,
+  setupTests,
+} from "./testing-utils";
+import { ConfigurationError, withTmpDir } from "./util";
 
 setupTests(test);
 
@@ -30,3 +42,91 @@ test("printPathFiltersWarning does not trigger when 'paths' and 'paths-ignore' a
   );
   t.is(messages.length, 0);
 });
+
+test("cleanupDatabaseClusterDirectory cleans up where possible", async (t) => {
+  await withTmpDir(async (tmpDir: string) => {
+    const dbLocation = path.resolve(tmpDir, "dbs");
+    fs.mkdirSync(dbLocation, { recursive: true });
+
+    const fileToCleanUp = path.resolve(dbLocation, "something-to-cleanup.txt");
+    fs.writeFileSync(fileToCleanUp, "");
+
+    const messages: LoggedMessage[] = [];
+    cleanupDatabaseClusterDirectory(
+      createTestConfig({ dbLocation }),
+      getRecordingLogger(messages),
+    );
+
+    t.is(messages.length, 2);
+    t.is(messages[0].type, "warning");
+    t.is(
+      messages[0].message,
+      `The database cluster directory ${dbLocation} must be empty. Attempting to clean it up.`,
+    );
+    t.is(messages[1].type, "info");
+    t.is(
+      messages[1].message,
+      `Cleaned up database cluster directory ${dbLocation}.`,
+    );
+
+    t.false(fs.existsSync(fileToCleanUp));
+  });
+});
+
+for (const { runnerEnv, ErrorConstructor, message } of [
+  {
+    runnerEnv: "self-hosted",
+    ErrorConstructor: ConfigurationError,
+    message: (dbLocation) =>
+      "The CodeQL Action requires an empty database cluster directory. By default, this is located " +
+      `at ${dbLocation}. You can customize it using the 'db-location' input to the init Action. An ` +
+      "attempt was made to clean up the directory, but this failed. This can happen if another " +
+      "process is using the directory or the directory is owned by a different user. Please clean " +
+      "up the directory manually and rerun the job.",
+  },
+  {
+    runnerEnv: "github-hosted",
+    ErrorConstructor: Error,
+    message: (dbLocation) =>
+      "The CodeQL Action requires an empty database cluster directory. By default, this is located " +
+      `at ${dbLocation}. You can customize it using the 'db-location' input to the init Action. An ` +
+      "attempt was made to clean up the directory, but this failed. This shouldn't typically " +
+      "happen on hosted runners. If you are using an advanced setup, please check your workflow, " +
+      "otherwise we recommend rerunning the job.",
+  },
+]) {
+  test(`cleanupDatabaseClusterDirectory throws a ${ErrorConstructor.name} when cleanup fails on ${runnerEnv} runner`, async (t) => {
+    await withTmpDir(async (tmpDir: string) => {
+      process.env["RUNNER_ENVIRONMENT"] = runnerEnv;
+
+      const dbLocation = path.resolve(tmpDir, "dbs");
+      fs.mkdirSync(dbLocation, { recursive: true });
+
+      const fileToCleanUp = path.resolve(
+        dbLocation,
+        "something-to-cleanup.txt",
+      );
+      fs.writeFileSync(fileToCleanUp, "");
+
+      const messages: LoggedMessage[] = [];
+      t.throws(
+        () =>
+          cleanupDatabaseClusterDirectory(
+            createTestConfig({ dbLocation }),
+            getRecordingLogger(messages),
+            () => {
+              throw new Error("Failed to clean up");
+            },
+          ),
+        { instanceOf: ErrorConstructor, message: message(dbLocation) },
+      );
+
+      t.is(messages.length, 1);
+      t.is(messages[0].type, "warning");
+      t.is(
+        messages[0].message,
+        `The database cluster directory ${dbLocation} must be empty. Attempting to clean it up.`,
+      );
+    });
+  });
+}