electron: fix backend forking

dev-packages/application-manager/src/generator/backend-generator.ts

@@ -27,6 +27,12 @@ export class BackendGenerator extends AbstractGenerator {
     protected compileServer(backendModules: Map<string, string>): string {
         return `// @ts-check
 require('reflect-metadata');
+
+// Patch electron version if missing, see https://github.com/eclipse-theia/theia/pull/7361#pullrequestreview-377065146
+if (typeof process.versions.electron === 'undefined' && typeof process.env.THEIA_ELECTRON_VERSION === 'string') {
+    process.versions.electron = process.env.THEIA_ELECTRON_VERSION;
+}
+
 const path = require('path');
 const express = require('express');
 const { Container } = require('inversify');

dev-packages/application-manager/src/generator/frontend-generator.ts

@@ -290,6 +290,8 @@ app.on('ready', () => {
     // Check whether we are in bundled application or development mode.
     // @ts-ignore
     const devMode = process.defaultApp || /node_modules[\/]electron[\/]/.test(process.execPath);
+    // Check if we should run everything as one process.
+    const noBackendFork = process.argv.includes('--no-cluster');
     const mainWindow = createNewWindow();
 
     if (isSingleInstance) {
@@ -327,17 +329,14 @@ app.on('ready', () => {
 
     // Set the electron version for both the dev and the production mode. (https://github.com/eclipse-theia/theia/issues/3254)
     // Otherwise, the forked backend processes will not know that they're serving the electron frontend.
-    const { versions } = process;
-    // @ts-ignore
-    if (versions && typeof versions.electron !== 'undefined') {
-        // @ts-ignore
-        process.env.THEIA_ELECTRON_VERSION = versions.electron;
-    }
+    // The forked backend should patch its \`process.versions.electron\` with this value if it is missing.
+    process.env.THEIA_ELECTRON_VERSION = process.versions.electron;
 
     const mainPath = join(__dirname, '..', 'backend', 'main');
-    // We need to distinguish between bundled application and development mode when starting the clusters.
-    // See: https://github.com/electron/electron/issues/6337#issuecomment-230183287
-    if (devMode) {
+    // We spawn a separate process for the backend for Express to not run in the Electron main process.
+    // See: https://github.com/eclipse-theia/theia/pull/7361#issuecomment-601272212
+    // But when in debugging we want to run everything in the same process to make things easier.
+    if (noBackendFork) {
         process.env[ElectronSecurityToken] = JSON.stringify(electronSecurityToken);
         require(mainPath).then(address => {
             loadMainWindow(address.port);
@@ -346,7 +345,10 @@ app.on('ready', () => {
             app.exit(1);
         });
     } else {
-        const cp = fork(mainPath, [], { env: Object.assign({
+        // We want to pass flags passed to the Electron app to the backend process.
+        // Quirk: When developing from sources, we execute Electron as \`electron.exe electron-main.js ...args\`, but when bundled,
+        // the command looks like \`bundled-application.exe ...args\`.
+        const cp = fork(mainPath, process.argv.slice(devMode ? 2 : 1), { env: Object.assign({
             [ElectronSecurityToken]: JSON.stringify(electronSecurityToken),
         }, process.env) });
         cp.on('message', (address) => {

dev-packages/application-package/src/environment.ts

@@ -32,9 +32,7 @@ class ElectronEnv {
      * Can be called from both the `main` and the render process. Also works for forked cluster workers.
      */
     is(): boolean {
-        // When forking a new process from the cluster, we can rely neither on `process.versions` nor `process.argv`.
-        // Se we look into the `process.env` as well. `is-electron` does not do it for us.
-        return isElectron() || typeof process !== 'undefined' && typeof process.env === 'object' && !!process.env.THEIA_ELECTRON_VERSION;
+        return isElectron();
     }
 
     /**

dev-packages/cli/README.md

@@ -34,6 +34,7 @@
   - [**Inspecting Tests**](#inspecting-tests)
   - [**Reporting Test Coverage**](#reporting-test-coverage)
 - [**Downloading Plugins**](#downloading-plugins)
+- [**Autogenerated Application**](#autogenerated-application)
 
 ## Description
 
@@ -270,6 +271,20 @@ The property `theiaPlugins` describes the list of plugins to download, for examp
 }
 ```
 
+## Autogenerated Application
+
+This package can auto-generate application code for both the backend and frontend, as well as webpack configuration files.
+
+When targeting Electron, the `electron-main.js` script will spawn the backend process in a Node.js sub-process, where Electron's API won't be available. To prevent the generated application from forking the backend, you can pass a `--no-cluster` flag. This flag is mostly useful/used for debugging.
+
+```sh
+# when developing a Theia application with @theia/cli:
+yarn theia start --no-cluster
+
+# when starting a bundled application made using @theia/cli:
+bundled-application.exe --no-cluster
+```
+
 ## Additional Information
 
 - [Theia - GitHub](https://github.com/eclipse-theia/theia)