goLanguageServer: set completion follow up command from middleware (#3084)

Author: hyangah

src/goLanguageServer.ts

@@ -12,6 +12,7 @@ import semver = require('semver');
 import util = require('util');
 import vscode = require('vscode');
 import {
+	Command,
 	FormattingOptions,
 	HandleDiagnosticsSignature,
 	LanguageClient,
@@ -143,6 +144,55 @@ export async function registerLanguageFeatures(ctx: vscode.ExtensionContext) {
 						return null;
 					}
 					return next(document, token);
+				},
+				provideCompletionItem: (
+					document: vscode.TextDocument,
+					position: vscode.Position,
+					context: vscode.CompletionContext,
+					token: vscode.CancellationToken,
+					next: ProvideCompletionItemsSignature
+				) => {
+					// TODO(hyangah): when v1.42+ api is available, we can simplify
+					// language-specific configuration lookup using the new
+					// ConfigurationScope.
+					//    const paramHintsEnabled = vscode.workspace.getConfiguration(
+					//          'editor.parameterHints',
+					//          { languageId: 'go', uri: document.uri });
+
+					const editorParamHintsEnabled = vscode.workspace.getConfiguration(
+						'editor.parameterHints', document.uri)['enabled'];
+					const goParamHintsEnabled = vscode.workspace.getConfiguration(
+						'[go]', document.uri)['editor.parameterHints.enabled'];
+
+					let paramHintsEnabled: boolean = false;
+					if (typeof goParamHintsEnabled === 'undefined') {
+						paramHintsEnabled = editorParamHintsEnabled;
+					} else {
+						paramHintsEnabled = goParamHintsEnabled;
+					}
+					let cmd: Command;
+					if (paramHintsEnabled) {
+						cmd = { title: 'triggerParameterHints', command: 'editor.action.triggerParameterHints' };
+					}
+
+					function configureCommands(
+						r: vscode.CompletionItem[] | vscode.CompletionList | null | undefined):
+						vscode.CompletionItem[] | vscode.CompletionList | null | undefined {
+						if (r) {
+							(Array.isArray(r) ? r : r.items).forEach((i: vscode.CompletionItem) => {
+								i.command = cmd;
+							});
+						}
+						return r;
+					}
+					const ret = next(document, position, context, token);
+
+					const isThenable = <T>(obj: vscode.ProviderResult<T>): obj is Thenable<T> => obj && (<any>obj)['then'];
+					if (isThenable<vscode.CompletionItem[] | vscode.CompletionList | null | undefined>(ret)) {
+						return ret.then(configureCommands);
+					}
+					return configureCommands(ret);
+
 				}
 			}
 		}