Add typescript-eslint-language-service (#30015)

webapp/channels/tsconfig.json

@@ -26,7 +26,10 @@
     "paths": {
         "mattermost-redux/*": ["packages/mattermost-redux/src/*"],
         "@mui/styled-engine": ["./node_modules/@mui/styled-engine-sc"],
-    }
+    },
+    "plugins": [{
+        "name": "typescript-eslint-language-service"
+    }]
   },
   "include": [
     "./src/**/*",

webapp/channels/webpack.config.js

@@ -18,10 +18,14 @@ const packageJson = require('./package.json');
 
 const NPM_TARGET = process.env.npm_lifecycle_event;
 
+// list of known code editors that set an environment variable.
+const knownCodeEditors = ['VSCODE_CWD', 'INSIDE_EMACS'];
+const isInsideCodeEditor = knownCodeEditors.some((editor) => process.env[editor]);
+
 const targetIsRun = NPM_TARGET?.startsWith('run');
 const targetIsStats = NPM_TARGET === 'stats';
 const targetIsDevServer = NPM_TARGET?.startsWith('dev-server');
-const targetIsEslint = NPM_TARGET?.startsWith('check') || NPM_TARGET === 'fix' || process.env.VSCODE_CWD;
+const targetIsEslint = NPM_TARGET?.startsWith('check') || NPM_TARGET === 'fix' || isInsideCodeEditor;
 
 const DEV = targetIsRun || targetIsStats || targetIsDevServer;