Add live error feedback as you type

package.json

@@ -541,6 +541,26 @@
           },
           "description": "Tags and options configured here will be used by the Add Tags command to add tags to struct fields. If promptForTags is true, then user will be prompted for tags and options. By default, json tags are added."
         },
+        "go.liveErrors": {
+          "type": "object",
+          "properties": {
+            "enabled": {
+            "type":"boolean",
+            "default":false,
+            "description": "If true, runs gotype on the file currently being edited and reports any semantic or syntactic errors found."
+            },
+            "delay": {
+              "type":"number",
+              "default":500,
+              "description": "The number of milliseconds to delay before execution. Resets with each keystroke."
+            }
+          },          
+          "default": {
+            "enabled": false,
+            "delay": 500
+          },
+          "description": "Tags and options configured here will be used to configure how the live errors system behaves."
+        },
         "go.removeTags": {
           "type": "object",
           "properties": {

src/goInstallTools.ts

@@ -14,6 +14,7 @@ import { showGoStatus, hideGoStatus } from './goStatus';
 import { getGoRuntimePath, resolvePath } from './goPath';
 import { outputChannel } from './goStatus';
 import { getBinPath, getToolsGopath, getGoVersion, SemVersion, isVendorSupported } from './util';
+import { goLiveErrorsEnabled } from './goLiveErrors';
 
 let updatesDeclinedTools: string[] = [];
 
@@ -28,6 +29,9 @@ function getTools(goVersion: SemVersion): { [key: string]: string } {
 		'gorename': 'golang.org/x/tools/cmd/gorename',
 		'gomodifytags': 'github.com/fatih/gomodifytags'
 	};
+	if (goLiveErrorsEnabled()) {
+		tools['gotype-live'] = 'github.com/tylerb/gotype-live';
+	}
 
 	// Install the doc/def tool that was chosen by the user
 	if (goConfig['docsTool'] === 'godoc') {

src/goLiveErrors.ts

@@ -0,0 +1,100 @@
+'use strict';
+
+import vscode = require('vscode');
+import { byteOffsetAt, getBinPath } from './util';
+import cp = require('child_process');
+import path = require('path');
+import { promptForMissingTool } from './goInstallTools';
+import { diagnosticCollection } from './goMain';
+
+// Interface for settings configuration for adding and removing tags
+interface GoLiveErrorsConfig {
+	delay: number;
+	enabled: boolean;
+}
+
+let runner;
+
+// parseLiveFile runs the gotype command in live mode to check for any syntactic or
+// semantic errors and reports them immediately
+export function parseLiveFile(e: vscode.TextDocumentChangeEvent) {
+	if (e.document.isUntitled) {
+		return;
+	}
+	if (e.document.languageId !== 'go') {
+		return;
+	}
+
+	let config = <GoLiveErrorsConfig>vscode.workspace.getConfiguration('go')['liveErrors'];
+	if (config == null || !config.enabled) {
+		return;
+	}
+
+	if (runner != null) {
+		clearTimeout(runner);
+	}
+	runner = setTimeout(function(){
+		processFile(e);
+		runner = null;
+	}, config.delay);
+}
+
+export function goLiveErrorsEnabled() {
+	return <GoLiveErrorsConfig>vscode.workspace.getConfiguration('go')['liveErrors'].enabled;
+}
+
+// processFile does the actual work once the timeout has fired
+function processFile(e: vscode.TextDocumentChangeEvent) {
+	let uri = e.document.uri;
+	let gotypeLive = getBinPath('gotype-live');
+	let fileContents = e.document.getText();
+	let fileName = e.document.fileName;
+	let args = ['-e', '-a', '-lf=' + fileName, path.dirname(fileName)];
+	let p = cp.execFile(gotypeLive, args, (err, stdout, stderr) => {
+		if (err && (<any>err).code === 'ENOENT') {
+			promptForMissingTool('gotype-live');
+			return;
+		}
+
+		// we want to take the error path here because the command we are calling
+		// returns a non-zero exit status if the checks fail
+		let newDiagnostics = [];
+		if (!newDiagnostics) {
+			newDiagnostics = [];
+		}
+
+		// grab a copy of the existing diagnostics that are being reported for the
+		// current file
+		let oldDiagnostics = diagnosticCollection.get(uri);
+
+		// delete the existing diagnostics for the current file
+		//
+		// error-level diagnostics will be reported by this process, so we want to
+		// clear out the existing errors to avoid getting duplicates
+		diagnosticCollection.delete(uri);
+
+		// we want to keep all non-error level diagnostics that were previously
+		// reported, so add them back in
+		oldDiagnostics.forEach((value) => {
+			if (value.severity !== vscode.DiagnosticSeverity.Error) {
+				newDiagnostics.push(value);
+			}
+		});
+
+		if (err) {
+			stderr.split('\n').forEach(error => {
+				if (error === null || error.length === 0) {
+					return;
+				}
+				// extract the line, column and error message from the gotype output
+				let [_, line, column, message] = /^.+:(\d+):(\d+):\s+(.+)/.exec(error);
+
+				let range = new vscode.Range(+line - 1, +column, +line - 1, +column);
+				let diagnostic = new vscode.Diagnostic(range, message, vscode.DiagnosticSeverity.Error);
+				newDiagnostics.push(diagnostic);
+			});
+		}
+		diagnosticCollection.set(uri, newDiagnostics);
+	});
+	p.stdin.end(fileContents);
+}

src/goMain.ts

@@ -32,8 +32,9 @@ import { isGoPathSet, getBinPath, sendTelemetryEvent } from './util';
 import { LanguageClient } from 'vscode-languageclient';
 import { clearCacheForTools } from './goPath';
 import { addTags, removeTags } from './goModifytags';
+import { parseLiveFile } from './goLiveErrors';
 
-let diagnosticCollection: vscode.DiagnosticCollection;
+export let diagnosticCollection: vscode.DiagnosticCollection;
 
 export function activate(ctx: vscode.ExtensionContext): void {
 	let useLangServer = vscode.workspace.getConfiguration('go')['useLanguageServer'];
@@ -87,6 +88,7 @@ export function activate(ctx: vscode.ExtensionContext): void {
 	vscode.workspace.onDidChangeTextDocument(removeTestStatus, null, ctx.subscriptions);
 	vscode.window.onDidChangeActiveTextEditor(showHideStatus, null, ctx.subscriptions);
 	vscode.window.onDidChangeActiveTextEditor(getCodeCoverage, null, ctx.subscriptions);
+	vscode.workspace.onDidChangeTextDocument(parseLiveFile, null, ctx.subscriptions);
 
 	startBuildOnSaveWatcher(ctx.subscriptions);