feat: add flag to disable shell mode for nest start --watch

When running on Linux/WSL, `nest start --watch` does not wait the app to shutdown on restart.
That leads to two instances of application running simultaneously, especially if it has async
shutdown hooks. That commit fixes that adding an option to disable shell mode when spawning
child processes so then app will completely shutdown first and only then started again.
Thanks @jleverenz for the investigation and solution idea in nestjs/nest-cli/1614

fixes nestjs/nest-cli/1614

actions/start.action.ts

@@ -72,12 +72,15 @@ export class StartAction extends BuildAction {
         commandOptions,
         defaultConfiguration.sourceRoot,
       );
+      const noShellOption = commandOptions.find((option) => option.name === 'noShell')
+      const useShell = noShellOption ? !noShellOption.value : true;
       const onSuccess = this.createOnSuccessHook(
         entryFile,
         sourceRoot,
         debugFlag,
         outDir,
         binaryToRun,
+        useShell,
       );
 
       await this.runBuild(
@@ -103,6 +106,7 @@ export class StartAction extends BuildAction {
     debugFlag: boolean | string | undefined,
     outDirName: string,
     binaryToRun: string,
+    useShell: boolean,
   ) {
     let childProcessRef: any;
     process.on(
@@ -120,6 +124,7 @@ export class StartAction extends BuildAction {
             debugFlag,
             outDirName,
             binaryToRun,
+            useShell,
           );
           childProcessRef.on('exit', () => (childProcessRef = undefined));
         });
@@ -133,6 +138,7 @@ export class StartAction extends BuildAction {
           debugFlag,
           outDirName,
           binaryToRun,
+          useShell,
         );
         childProcessRef.on('exit', (code: number) => {
           process.exitCode = code;
@@ -148,6 +154,7 @@ export class StartAction extends BuildAction {
     debug: boolean | string | undefined,
     outDirName: string,
     binaryToRun: string,
+    useShell: boolean,
   ) {
     let outputFilePath = join(outDirName, sourceRoot, entryFile);
     if (!fs.existsSync(outputFilePath + '.js')) {
@@ -179,7 +186,7 @@ export class StartAction extends BuildAction {
 
     return spawn(binaryToRun, processArgs, {
       stdio: 'inherit',
-      shell: true,
+      shell: useShell,
     });
   }
 }

commands/start.command.ts

@@ -38,6 +38,7 @@ export class StartCommand extends AbstractCommand {
         '--preserveWatchOutput',
         'Use "preserveWatchOutput" option when using tsc watch mode.',
       )
+      .option('--noShell', 'Spawn child processes without shell (see node\'s child_process.spawn() method docs)')
       .description('Run Nest application.')
       .action(async (app: string, command: Command) => {
         const options: Input[] = [];
@@ -79,6 +80,10 @@ export class StartCommand extends AbstractCommand {
             !!command.watch &&
             !isWebpackEnabled,
         });
+        options.push({
+          name: 'noShell',
+          value: !!command.noShell,
+        })
 
         const availableBuilders = ['tsc', 'webpack', 'swc'];
         if (command.builder && !availableBuilders.includes(command.builder)) {