Pass environment variables to LSP

package.json

@@ -144,6 +144,12 @@
           "default": "",
           "markdownDescription": "Pass additional arguments to the language server."
         },
+        "haskell.envVars": {
+          "scope": "resource",
+          "type": "object",
+          "default": {},
+          "markdownDescription": "Define environment variables for compilation/execution."
+        },
         "haskell.updateBehavior": {
           "scope": "machine",
           "type": "string",

src/extension.ts

@@ -25,6 +25,11 @@ import { DocsBrowser } from './docsBrowser';
 import { downloadHaskellLanguageServer } from './hlsBinaries';
 import { directoryExists, executableExists, ExtensionLogger, resolvePathPlaceHolders } from './utils';
 
+// Used for environment variables later on
+interface IEnvVars {
+  [key: string]: string;
+}
+
 // 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,
 // in which case don't try to launch another one for that uri
@@ -212,8 +217,10 @@ async function activateServerForFolder(context: ExtensionContext, uri: Uri, fold
     logger.info(`Activating the language server in the parent dir of the file: ${uri.fsPath}`);
   }
 
+  const envVars: IEnvVars = workspace.getConfiguration('haskell', uri).envVars;
   const exeOptions: ExecutableOptions = {
     cwd: folder ? undefined : path.dirname(uri.fsPath),
+    env: Object.assign(process.env, envVars),
   };
 
   // We don't want empty strings in our args