Introduce 'automatic' mode for 'supportCabalFiles' option

Add option to automatically determine whether the Haskell Language
Server binary we are about to launch supports '.cabal' files.
If not, i.e. the HLS binary is older than '1.9.0.0', then we do not send
file notifications for '.cabal' files. Otherwise, we do send these
notifications.

The user can explicitly overwrite this option in order to avoid the
version check.

Author: fendor

package.json

@@ -236,9 +236,19 @@
         },
         "haskell.supportCabalFiles": {
           "scope": "resource",
-          "default": true,
-          "type": "boolean",
-          "description": "Enable Language Server support for `.cabal` files. Requires Haskell Language Server version >= 2.0.0.0."
+          "default": "automatic",
+          "type": "string",
+          "enum": [
+            "enable",
+            "disable",
+            "automatic"
+          ],
+          "description": "Enable Language Server support for `.cabal` files. Requires Haskell Language Server version >= 1.9.0.0.",
+          "enumDescriptions": [
+            "Enable Language Server support for `.cabal` files",
+            "Disable Language Server support for `.cabal` files",
+            "Enable Language Server support for `.cabal` files if the HLS version supports it."
+          ]
         },
         "haskell.maxCompletions": {
           "scope": "resource",

src/extension.ts

@@ -21,8 +21,8 @@ import {
 import { RestartServerCommandName, StartServerCommandName, StopServerCommandName } from './commands/constants';
 import * as DocsBrowser from './docsBrowser';
 import { HlsError, MissingToolError, NoMatchingHls } from './errors';
-import { findHaskellLanguageServer, IEnvVars } from './hlsBinaries';
-import { addPathToProcessPath, expandHomeDir, ExtensionLogger } from './utils';
+import { callAsync, findHaskellLanguageServer, IEnvVars } from './hlsBinaries';
+import { addPathToProcessPath, comparePVP, expandHomeDir, ExtensionLogger } from './utils';
 
 // The current map of documents & folders to language servers.
 // It may be null to indicate that we are in the process of launching a server,
@@ -205,8 +205,11 @@ async function activateServerForFolder(context: ExtensionContext, uri: Uri, fold
     args = args.concat(extraArgs.split(' '));
   }
 
-  const cabalFileSupport: boolean = workspace.getConfiguration('haskell', uri).supportCabalFiles;
-  logger.info(`Support for '.cabal' files enabled: ${cabalFileSupport ? 'yes' : 'no'}`);
+  const cabalFileSupport: 'automatic' | 'enable' | 'disable' = workspace.getConfiguration(
+    'haskell',
+    uri,
+  ).supportCabalFiles;
+  logger.info(`Support for '.cabal' files: ${cabalFileSupport}`);
 
   // If we're operating on a standalone file (i.e. not in a folder) then we need
   // to launch the server in a reasonable current directory. Otherwise the cradle
@@ -257,20 +260,43 @@ async function activateServerForFolder(context: ExtensionContext, uri: Uri, fold
   const pat = folder ? `${folder.uri.fsPath}/**/*` : '**/*';
   logger.log(`document selector patten: ${pat}`);
 
-
-  const cabalDocumentSelector = cabalFileSupport ? [{ scheme: 'file', language: 'cabal', pattern: pat }] : [];
+  const cabalDocumentSelector = { scheme: 'file', language: 'cabal', pattern: pat };
   const haskellDocumentSelector = [
     { scheme: 'file', language: 'haskell', pattern: pat },
     { scheme: 'file', language: 'literate haskell', pattern: pat },
   ];
 
+  const documentSelector = [...haskellDocumentSelector];
+
+  switch (cabalFileSupport) {
+    case 'automatic':
+      const hlsVersion = await callAsync(
+        serverExecutable,
+        ['--numeric-version'],
+        logger,
+        currentWorkingDir,
+        undefined /* this command is very fast, don't show anything */,
+        false,
+        serverEnvironment,
+      );
+      if (comparePVP(hlsVersion, '1.9.0.0') >= 0) {
+        // If hlsVersion is >= '1.9.0.0'
+        documentSelector.push(cabalDocumentSelector);
+      }
+      break;
+    case 'enable':
+      documentSelector.push(cabalDocumentSelector);
+      break;
+    case 'disable':
+      break;
+    default:
+      break;
+  }
+
   const clientOptions: LanguageClientOptions = {
     // Use the document selector to only notify the LSP on files inside the folder
     // path for the specific workspace.
-    documentSelector:
-      [ ... haskellDocumentSelector
-      , ... cabalDocumentSelector
-      ],
+    documentSelector: [...documentSelector],
     synchronize: {
       // Synchronize the setting section 'haskell' to the server.
       configurationSection: 'haskell',

src/hlsBinaries.ts

@@ -58,7 +58,7 @@ type ProcessCallback = (
  * @param callback Upon process termination, execute this callback. If given, must resolve promise. On error, stderr and stdout are logged regardless of whether the callback has been specified.
  * @returns Stdout of the process invocation, trimmed off newlines, or whatever the `callback` resolved to.
  */
-async function callAsync(
+export async function callAsync(
   binary: string,
   args: string[],
   logger: Logger,