Add item documentation to completions (#2054)

* Add item documentation to completions

Using `go doc` instead of `godoc` due to
golang/go#25443

`go doc` doesn't seem to support giving the code of an unsaved file via
stdin like `gocode`, so it won't display documentation for unsaved
changes.

Fixes #194

* Code review fixes for #2054

* Refactoring and comments

* Always resolve the item

* Prompt for updating gocode if the package property is missing

Author: segevfiner

src/goSuggest.ts

@@ -41,10 +41,16 @@ function vscodeKindFromGoCodeClass(kind: string, type: string): vscode.Completio
 
 interface GoCodeSuggestion {
 	class: string;
+	package?: string;
 	name: string;
 	type: string;
 }
 
+class ExtendedCompletionItem extends vscode.CompletionItem {
+	package?: string;
+	fileName: string;
+}
+
 const lineCommentRegex = /^\s*\/\/\s+/;
 const exportedMemberRegex = /(const|func|type|var)(\s+\(.*\))?\s+([A-Z]\w*)/;
 const gocodeNoSupportForgbMsgKey = 'dontshowNoSupportForgb';
@@ -75,6 +81,49 @@ export class GoCompletionItemProvider implements vscode.CompletionItemProvider {
 		});
 	}
 
+	public resolveCompletionItem(item: vscode.CompletionItem, token: vscode.CancellationToken): vscode.ProviderResult<vscode.CompletionItem> {
+		const goRuntimePath = getBinPath('go');
+		if (!goRuntimePath || !(item instanceof ExtendedCompletionItem)) {
+			return;
+		}
+
+		if (typeof item.package === 'undefined') {
+			promptForUpdatingTool('gocode');
+			return;
+		}
+
+		const env = getToolsEnvVars();
+		const cwd = path.dirname(item.fileName);
+
+		return new Promise<vscode.CompletionItem>(resolve => {
+			const args = ['doc', '-c', '-cmd', '-u'];
+			if (item.package) {
+				args.push(item.package, item.label);
+			} else {
+				// item.package would be empty for symbols from the current package
+				args.push(item.label);
+			}
+
+			cp.execFile(goRuntimePath, args, { cwd, env }, (err, stdout) => {
+				if (err) {
+					console.log(err);
+					return resolve(item);
+				}
+
+				let doc = '';
+				const goDocLines = stdout.toString().split('\n');
+				// i = 1 to skip the func signature line
+				for (let i = 1; i < goDocLines.length && goDocLines[i].startsWith('    '); i++) {
+					doc += goDocLines[i].substring(4) + '\n';
+				}
+
+				item.documentation = doc;
+				resolve(item);
+			});
+		});
+
+	}
+
 	public provideCompletionItemsInternal(document: vscode.TextDocument, position: vscode.Position, token: vscode.CancellationToken, config: vscode.WorkspaceConfiguration): Thenable<vscode.CompletionItem[] | vscode.CompletionList> {
 		return this.ensureGoCodeConfigured(document.uri).then(() => {
 			return new Promise<vscode.CompletionItem[] | vscode.CompletionList>((resolve, reject) => {
@@ -228,9 +277,11 @@ export class GoCompletionItemProvider implements vscode.CompletionItemProvider {
 					if (results && results[1]) {
 						for (let suggest of results[1]) {
 							if (inString && suggest.class !== 'import') continue;
-							let item = new vscode.CompletionItem(suggest.name);
+							let item = new ExtendedCompletionItem(suggest.name);
 							item.kind = vscodeKindFromGoCodeClass(suggest.class, suggest.type);
 							item.detail = suggest.type;
+							item.package = suggest.package;
+							item.fileName = document.fileName;
 							if (inString && suggest.class === 'import') {
 								item.textEdit = new vscode.TextEdit(
 									new vscode.Range(
@@ -454,4 +505,4 @@ export class GoCompletionItemProvider implements vscode.CompletionItemProvider {
 		});
 		return matchingPackages;
 	}
-}
+}