fix: use ChildProcess type for LanguageServerProcess

lsProcess is spawned using a `spawn` function of `child_process`. 
That means hiding the types behind an extended type can result in bugs.

This is also simpler as we don't need to maintain the types for 
LanguageServerProcess

Author: aminya

lib/auto-languageclient.ts

@@ -283,7 +283,7 @@ export default class AutoLanguageClient {
    *  Use this inside the `startServerProcess` override if the language server is a general executable
    *  Also see the `spawnChildNode` method
    */
-  protected spawn(exe: string, args: string[], options: cp.SpawnOptions = {}): cp.ChildProcess {
+  protected spawn(exe: string, args: string[], options: cp.SpawnOptions = {}): LanguageServerProcess {
     this.logger.debug(`starting "${exe} ${args.join(' ')}"`);
     return cp.spawn(exe, args, options);
   }
@@ -292,7 +292,7 @@ export default class AutoLanguageClient {
    *  Use this inside the `startServerProcess` override if the language server is a JavaScript file.
    *  Also see the `spawn` method
    */
-  protected spawnChildNode(args: string[], options: cp.SpawnOptions = {}): cp.ChildProcess {
+  protected spawnChildNode(args: string[], options: cp.SpawnOptions = {}): LanguageServerProcess {
     this.logger.debug(`starting child Node "${args.join(' ')}"`);
     options.env = options.env || Object.create(process.env);
     if (options.env) {
@@ -370,8 +370,8 @@ export default class AutoLanguageClient {
     lsProcess.on('error', (err) => this.handleSpawnFailure(err));
     lsProcess.on("close", (...args) => this.handleCloseFailure(...args));
     lsProcess.on('exit', (code, signal) => this.logger.debug(`exit: code ${code} signal ${signal}`));
-    lsProcess.stderr.setEncoding('utf8');
-    lsProcess.stderr.on('data', (chunk: Buffer) => {
+    lsProcess.stderr?.setEncoding('utf8');
+    lsProcess.stderr?.on('data', (chunk: Buffer) => {
       const errorString = chunk.toString();
       this.handleServerStderr(errorString, projectPath);
       // Keep the last 5 lines for packages to use in messages
@@ -415,8 +415,13 @@ export default class AutoLanguageClient {
         writer = new rpc.SocketMessageWriter(this.socket);
         break;
       case 'stdio':
-        reader = new rpc.StreamMessageReader(lsProcess.stdout);
-        writer = new rpc.StreamMessageWriter(lsProcess.stdin);
+        if (lsProcess.stdin !== null && lsProcess.stdout !== null) {
+          reader = new rpc.StreamMessageReader(lsProcess.stdout);
+          writer = new rpc.StreamMessageWriter(lsProcess.stdin);
+        } else {
+          this.logger.error(`The language server process for ${this.getLanguageName()} does not have a valid stdin and stdout`);
+          return Utils.assertUnreachable('stdio' as never)
+        }
         break;
       default:
         return Utils.assertUnreachable(connectionType);

lib/server-manager.ts

@@ -1,8 +1,7 @@
 import Convert from './convert';
 import * as path from 'path';
-import * as stream from 'stream';
 import * as ls from './languageclient';
-import { EventEmitter } from 'events';
+import { ChildProcess } from 'child_process'
 import { Logger } from './logger';
 import {
   CompositeDisposable,
@@ -11,24 +10,16 @@ import {
 } from 'atom';
 import { ReportBusyWhile } from './utils';
 
+
+type MinimalLanguageServerProcess = Pick<ChildProcess, 'stdin' | 'stdout' | 'stderr' | 'pid' | 'kill' | 'on'>
+
 /**
- * Public: Defines the minimum surface area for an object that resembles a
- * ChildProcess.  This is used so that language packages with alternative
- * language server process hosting strategies can return something compatible
- * with AutoLanguageClient.startServerProcess.
+ * Public: Defines a language server process which is either a ChildProcess, or it is a minimal object that resembles a
+ * ChildProcess.
+ * `MinimalLanguageServerProcess` is used so that language packages with alternative language server process hosting strategies
+ * can return something compatible with `AutoLanguageClient.startServerProcess`.
  */
-export interface LanguageServerProcess extends EventEmitter {
-  stdin: stream.Writable;
-  stdout: stream.Readable;
-  stderr: stream.Readable;
-  pid: number;
-
-  kill(signal?: NodeJS.Signals | number): void;
-  on(event: 'close', listener: (code: number | null, signal: NodeJS.Signals | null) => void): this;
-  on(event: 'disconnect', listener: () => void): this;
-  on(event: 'error', listener: (err: Error) => void): this;
-  on(event: 'exit', listener: (code: number | null, signal: NodeJS.Signals | null) => void): this;
-}
+export type LanguageServerProcess = ChildProcess | MinimalLanguageServerProcess
 
 /** The necessary elements for a server that has started or is starting. */
 export interface ActiveServer {