re-fix configuration provider initialization (#1386)

Author: sailingKieler

packages/langium/src/lsp/language-server.ts

@@ -199,13 +199,16 @@ export class DefaultLanguageServer implements LanguageServer {
         const configurationParams = connection ? <ConfigurationInitializedParams>{
             ...params,
             register: params => connection.client.register(DidChangeConfigurationNotification.type, params),
-            getConfiguration: params => connection.workspace.getConfiguration(params)
+            fetchConfiguration: params => connection.workspace.getConfiguration(params)
         } : params;
 
-        this.services.workspace.WorkspaceManager.initialized(params)
-            .catch(err => console.error('Error in WorkspaceManager initialization:', err));
+        // do not await the promises of the following calls, as they must not block the initialization process!
+        //  otherwise, there is the danger of out-of-order processing of subsequent incoming messages from the language client
+        // however, awaiting should be possible in general, e.g. in unit test scenarios
         this.services.workspace.ConfigurationProvider.initialized(configurationParams)
             .catch(err => console.error('Error in ConfigurationProvider initialization:', err));
+        this.services.workspace.WorkspaceManager.initialized(params)
+            .catch(err => console.error('Error in WorkspaceManager initialization:', err));
     }
 }
 

packages/langium/src/workspace/configuration.ts

@@ -4,10 +4,7 @@
  * terms of the MIT License, which is available in the project root.
  ******************************************************************************/
 
-import type {
-    ConfigurationItem, DidChangeConfigurationParams, DidChangeConfigurationRegistrationOptions, InitializeParams,
-    InitializedParams
-} from 'vscode-languageserver-protocol';
+import type { ConfigurationItem, DidChangeConfigurationParams, DidChangeConfigurationRegistrationOptions, InitializeParams, InitializedParams } from 'vscode-languageserver-protocol';
 import type { ServiceRegistry } from '../service-registry.js';
 import type { LangiumSharedCoreServices } from '../services.js';
 
@@ -46,7 +43,7 @@ export interface ConfigurationProvider {
 
 export interface ConfigurationInitializedParams extends InitializedParams {
     register?: (params: DidChangeConfigurationRegistrationOptions) => void,
-    getConfiguration?: (configuration: ConfigurationItem[]) => Promise<any>
+    fetchConfiguration?: (configuration: ConfigurationItem[]) => Promise<any>
 }
 
 /**
@@ -57,6 +54,7 @@ export class DefaultConfigurationProvider implements ConfigurationProvider {
     protected readonly serviceRegistry: ServiceRegistry;
     protected settings: Record<string, Record<string, any>> = {};
     protected workspaceConfig = false;
+    protected fetchConfiguration: ((configurations: ConfigurationItem[]) => Promise<any>) | undefined;
 
     constructor(services: LangiumSharedCoreServices) {
         this.serviceRegistry = services.ServiceRegistry;
@@ -79,20 +77,34 @@ export class DefaultConfigurationProvider implements ConfigurationProvider {
                 });
             }
 
-            if (params.getConfiguration) {
-                // params.getConfiguration(...) is a function to be provided by the calling language server for the sake of
-                //  decoupling this implementation from the concrete LSP implementations, specifically the LSP Connection
+            // params.fetchConfiguration(...) is a function to be provided by the calling language server for the sake of
+            //  decoupling this implementation from the concrete LSP implementations, specifically the LSP Connection
+            this.fetchConfiguration = params.fetchConfiguration;
 
-                const configToUpdate = this.serviceRegistry.all.map(lang => <ConfigurationItem>{
-                    // Fetch the configuration changes for all languages
-                    section: this.toSectionName(lang.LanguageMetaData.languageId)
-                });
-                // get workspace configurations (default scope URI)
-                const configs = await params.getConfiguration(configToUpdate);
-                configToUpdate.forEach((conf, idx) => {
-                    this.updateSectionConfiguration(conf.section!, configs[idx]);
-                });
-            }
+            // awaiting the fetch of the initial configuration data must not happen here, because it would block the
+            //  initialization of the language server, and may lead to out-of-order processing of subsequent messages from the language client;
+            // fetching the initial configuration in a non-blocking manner might cause a read-before-write problem
+            //  in case the workspace initialization relies on that configuration data (which is the case for the grammar language server);
+            // consequently, we fetch the initial configuration data on blocking manner on-demand, when the first configuration value is read,
+            //  see below in #getConfiguration(...);
+        }
+    }
+
+    protected async initializeConfiguration(): Promise<void> {
+        if (this.fetchConfiguration) {
+            const configToUpdate = this.serviceRegistry.all.map(lang => <ConfigurationItem>{
+                // Fetch the configuration changes for all languages
+                section: this.toSectionName(lang.LanguageMetaData.languageId)
+            });
+
+            // get workspace configurations (default scope URI)
+            const configs = await this.fetchConfiguration(configToUpdate);
+            configToUpdate.forEach((conf, idx) => {
+                this.updateSectionConfiguration(conf.section!, configs[idx]);
+            });
+
+            // reset the 'fetchConfiguration' to 'undefined' again in order to prevent further 'fetch' attempts
+            this.fetchConfiguration = undefined;
         }
     }
 
@@ -122,6 +134,8 @@ export class DefaultConfigurationProvider implements ConfigurationProvider {
     * @param configuration Configuration name
     */
     async getConfiguration(language: string, configuration: string): Promise<any> {
+        await this.initializeConfiguration();
+
         const sectionName = this.toSectionName(language);
         if (this.settings[sectionName]) {
             return this.settings[sectionName][configuration];