New configuration parameter "forceLegacyMode"

package.json

@@ -165,6 +165,14 @@
       "title": "Rust extension configuration",
       "type": "object",
       "properties": {
+        "rust.forceLegacyMode": {
+          "type": [
+            "boolean",
+            "null"
+          ],
+          "default": null,
+          "description": "Flag indicating if the extension shouldn't try to run RLS. By default, it is false"
+        },
         "rust.racerPath": {
           "type": [
             "string",

src/components/configuration/Configuration.ts

@@ -30,11 +30,18 @@ export enum ActionOnStartingCommandIfThereIsRunningCommand {
     ShowDialogToLetUserDecide
 }
 
+export enum Mode {
+    Legacy,
+    RLS
+}
+
 /**
  * The main class of the component `Configuration`.
  * This class contains code related to Configuration
  */
 export class Configuration {
+    private _mode: Mode | undefined;
+    private _isForcedLegacyMode: boolean;
     private logger: ChildLogger;
 
     private rustInstallation: Rustup | NotRustup | undefined;
@@ -71,33 +78,28 @@ export class Configuration {
      */
     public static async create(logger: ChildLogger): Promise<Configuration> {
         const rustcSysRoot: string | undefined = await this.loadRustcSysRoot();
-
         const createRustInstallationPromise = async () => {
             if (!rustcSysRoot) {
                 return undefined;
             }
-
             if (Rustup.doesManageRustcSysRoot(rustcSysRoot)) {
                 return await Rustup.create(logger.createChildLogger('Rustup: '), rustcSysRoot);
             } else {
                 return new NotRustup(rustcSysRoot);
             }
         };
-
         const rustInstallation: Rustup | NotRustup | undefined = await createRustInstallationPromise();
-
         const pathToRustSourceCodeSpecifiedByUser = await this.checkPathToRustSourceCodeSpecifiedByUser();
-
         const configuration = new Configuration(
             logger,
             rustInstallation,
             pathToRustSourceCodeSpecifiedByUser,
             undefined,
             undefined
         );
-
-        await configuration.updatePathToRlsExecutableSpecifiedByUser();
-
+        if (!configuration.isForcedLegacyMode()) {
+            await configuration.updatePathToRlsExecutableSpecifiedByUser();
+        }
         return configuration;
     }
 
@@ -140,6 +142,22 @@ export class Configuration {
         );
     }
 
+    public mode(): Mode | undefined {
+        return this._mode;
+    }
+
+    public setMode(mode: Mode): void {
+        if (this._mode !== undefined) {
+            this.logger.createChildLogger(`setMode(${mode}): `).error('this._mode !== undefined. The method should not have been called');
+            return;
+        }
+        this._mode = mode;
+    }
+
+    public isForcedLegacyMode(): boolean {
+        return this._isForcedLegacyMode;
+    }
+
     /**
      * Returns a value of the field `pathToRacer`
      */
@@ -251,14 +269,11 @@ export class Configuration {
 
     public shouldExecuteCargoCommandInTerminal(): boolean {
         // When RLS is used any cargo command is executed in an integrated terminal.
-        if (this.getRlsConfiguration() !== undefined) {
+        if (this.mode() === Mode.RLS) {
             return true;
         }
-
         const configuration = Configuration.getConfiguration();
-
         const shouldExecuteCargoCommandInTerminal = configuration['executeCargoCommandInTerminal'];
-
         return shouldExecuteCargoCommandInTerminal;
     }
 
@@ -453,14 +468,22 @@ export class Configuration {
         rlsPathSpecifiedByUser: string | undefined,
         pathToRacer: string | undefined
     ) {
+        function isForcedLegacyMode(): boolean {
+            const configuration = Configuration.getConfiguration();
+            const value: boolean | null | undefined = configuration['forceLegacyMode'];
+            if (value) {
+                // It is actually `true`, but who knows how the code would behave later
+                return value;
+            } else {
+                return false;
+            }
+        }
+        this._mode = undefined;
+        this._isForcedLegacyMode = isForcedLegacyMode();
         this.logger = logger;
-
         this.rustInstallation = rustInstallation;
-
         this.pathToRustSourceCodeSpecifiedByUser = pathToRustSourceCodeSpecifiedByUser;
-
         this.rlsPathSpecifiedByUser = rlsPathSpecifiedByUser;
-
         this.racerPath = pathToRacer;
     }
 
@@ -479,6 +502,10 @@ export class Configuration {
      */
     private async updatePathToRlsExecutableSpecifiedByUser(): Promise<void> {
         const logger = this.logger.createChildLogger('updatePathToRlsSpecifiedByUser: ');
+        if (this.mode() === Mode.Legacy) {
+            logger.error('this.mode() === Mode.Legacy. The method should not have been called');
+            return;
+        }
         this.rlsPathSpecifiedByUser = undefined;
         const rlsConfiguration = this.getRlsConfiguration();
         if (!rlsConfiguration) {

src/extension.ts

@@ -5,7 +5,7 @@ import { ExtensionContext, window, workspace } from 'vscode';
 
 import { CargoManager, CommandInvocationReason } from './components/cargo/cargo_manager';
 
-import { Configuration } from './components/configuration/Configuration';
+import { Configuration, Mode } from './components/configuration/Configuration';
 
 import CurrentWorkingDirectoryManager from './components/configuration/current_working_directory_manager';
 
@@ -129,7 +129,7 @@ export async function activate(ctx: ExtensionContext): Promise<void> {
     const loggingManager = new LoggingManager();
     const logger = loggingManager.getLogger();
     const configuration = await Configuration.create(logger.createChildLogger('Configuration: '));
-    if (!configuration.getPathToRlsExecutable()) {
+    if (!configuration.getPathToRlsExecutable() && !configuration.isForcedLegacyMode()) {
         await handleMissingRls(logger, configuration);
     }
     const currentWorkingDirectoryManager = new CurrentWorkingDirectoryManager();
@@ -181,11 +181,10 @@ async function chooseModeAndRun(
     configuration: Configuration,
     currentWorkingDirectoryManager: CurrentWorkingDirectoryManager
 ): Promise<void> {
-    const pathToRlsExecutable = configuration.getPathToRlsExecutable();
-
-    if (pathToRlsExecutable) {
-        runInRlsMode(context, logger, configuration, pathToRlsExecutable);
-    } else {
+    const rls: string | undefined = configuration.getPathToRlsExecutable();
+    const isLegacyMode = configuration.isForcedLegacyMode() || !rls;
+    if (isLegacyMode) {
+        configuration.setMode(Mode.Legacy);
         const legacyModeManager = await LegacyModeManager.create(
             context,
             configuration,
@@ -194,6 +193,9 @@ async function chooseModeAndRun(
         );
 
         await legacyModeManager.start();
+    } else {
+        configuration.setMode(Mode.RLS);
+        runInRlsMode(context, logger, configuration, <string>rls);
     }
 }
 

tslint.json

@@ -39,7 +39,12 @@
         ]
       }
     ],
-    "prefer-const": [true, {"destructuring": "all"}],
+    "prefer-const": [
+      true,
+      {
+        "destructuring": "all"
+      }
+    ],
     "no-any": false,
     "no-arg": true,
     "no-bitwise": false,
@@ -106,6 +111,7 @@
     "variable-name": [
       true,
       "check-format",
+      "allow-leading-underscore",
       "ban-keywords"
     ],
     "whitespace": [