fix(cli): ensure an empty event loop counts as an error (#6399)

**What's the problem this PR addresses?**

If the event loop unexpectedly becomes empty `yarn` will terminate with
exit code 0 even though the command didn't complete successfully.

Ref nodejs/node#53902

Ref #6398 where that happens and
the install is incomplete when `yarn` terminates with exit code 0. It's
caught in the following `yarn build` step which can't find the install
state.

**How did you fix it?**

Set `process.exitCode` to an error code before executing the CLI so an
unexpected empty event loop counts as an error.

**Checklist**
- [x] I have read the [Contributing
Guide](https://yarnpkg.com/advanced/contributing).
- [x] I have set the packages that need to be released for my changes to
be effective.
- [x] I will check that all automated PR checks pass before the PR gets
reviewed.

Author: merceyz

.yarn/versions/3a4fece1.yml

@@ -0,0 +1,23 @@
+releases:
+  "@yarnpkg/cli": patch
+
+declined:
+  - "@yarnpkg/plugin-compat"
+  - "@yarnpkg/plugin-constraints"
+  - "@yarnpkg/plugin-dlx"
+  - "@yarnpkg/plugin-essentials"
+  - "@yarnpkg/plugin-init"
+  - "@yarnpkg/plugin-interactive-tools"
+  - "@yarnpkg/plugin-nm"
+  - "@yarnpkg/plugin-npm-cli"
+  - "@yarnpkg/plugin-pack"
+  - "@yarnpkg/plugin-patch"
+  - "@yarnpkg/plugin-pnp"
+  - "@yarnpkg/plugin-pnpm"
+  - "@yarnpkg/plugin-stage"
+  - "@yarnpkg/plugin-typescript"
+  - "@yarnpkg/plugin-version"
+  - "@yarnpkg/plugin-workspace-tools"
+  - "@yarnpkg/builder"
+  - "@yarnpkg/core"
+  - "@yarnpkg/doctor"

packages/acceptance-tests/pkg-tests-specs/sources/commands/install.test.ts

@@ -900,5 +900,30 @@ describe(`Commands`, () => {
         });
       }),
     );
+
+    test(`it should exit with an error code after an unexpected empty event loop`,
+      makeTemporaryEnv({}, async ({path, run}) => {
+        await xfs.writeFilePromise(ppath.join(path, `plugin.cjs`), `
+module.exports = {
+  name: 'test',
+  factory() {
+    return {
+      hooks: {
+        afterAllInstalled: () => new Promise(() => {}),
+      },
+    };
+  },
+};
+`);
+        await xfs.writeJsonPromise(ppath.join(path, Filename.rc), {
+          plugins: [`./plugin.cjs`],
+        });
+
+        await expect(run(`install`)).rejects.toMatchObject({
+          code: 42,
+          stdout: expect.stringContaining(`Yarn is terminating due to an unexpected empty event loop`),
+        });
+      }),
+    );
   });
 });

packages/yarnpkg-cli/sources/lib.ts

@@ -186,12 +186,24 @@ export async function getCli({cwd = ppath.cwd(), pluginConfiguration = getPlugin
 export async function runExit(argv: Array<string>, {cwd = ppath.cwd(), selfPath, pluginConfiguration}: {cwd: PortablePath, selfPath: PortablePath | null, pluginConfiguration: PluginConfiguration}) {
   const cli = getBaseCli({cwd, pluginConfiguration});
 
+  function unexpectedTerminationHandler() {
+    Cli.defaultContext.stdout.write(`ERROR: Yarn is terminating due to an unexpected empty event loop.\nPlease report this issue at https://github.com/yarnpkg/berry/issues.`);
+  }
+
+  process.once(`beforeExit`, unexpectedTerminationHandler);
+
   try {
+    // The exit code is set to an error code before the CLI runs so that
+    // if the event loop becomes empty and node terminates without
+    // finishing the execution of this function it counts as an error.
+    // https://github.com/yarnpkg/berry/issues/6398
+    process.exitCode = 42;
     process.exitCode = await run(cli, argv, {selfPath, pluginConfiguration});
   } catch (error) {
     Cli.defaultContext.stdout.write(cli.error(error));
     process.exitCode = 1;
   } finally {
+    process.off(`beforeExit`, unexpectedTerminationHandler);
     await xfs.rmtempPromise();
   }
 }