How to run `go fmt` on save, in Visual Studio Code?

How to make Visual Studio Code (or Go Programming Language Extension) to run go fmt (or other tools/commands) on save? Even auto save?

Update:
It is working now perfectly inside VSCode, at this time; just need to add some config files inside .vscode directory (I use these).

Update 2019:
This question is old. The VSCode Go extension has all you need to develop in Go, now.

Last Update 2019
BTW It worth mentioning that right above the package declaration inside your test files appears a run package tests. If you click it, you can see your code coverage of your code. The covered and not-covered parts are highlighted in different colors.

Update 2020
And now, the Go Extension for VSCode, is under the supervision of Go Team! 🎉

Now, the feature has been implemented, you can enable format on save:

1. Open Settings (Ctrl + ,)
2. Search for editor.formatOnSave and set it to true

Your Go code will be formatted automatically on Ctrl + s

Its not possible at the moment but its being worked on https://github.com/Microsoft/vscode-go/issues/14

I'm not familiar with 'go fmt' specifically, but you can create a simple vscode extension to handle on save event and execute any arbitrary command passing the file path as an argument.

Here's a sample that just calls echo $filepath:

import * as vscode from 'vscode';
import {exec} from 'child_process';

export function activate(context: vscode.ExtensionContext) {

	vscode.window.showInformationMessage('Run command on save enabled.');

	var cmd = vscode.commands.registerCommand('extension.executeOnSave', () => {

		var onSave = vscode.workspace.onDidSaveTextDocument((e: vscode.TextDocument) => {

			// execute some child process on save
			var child = exec('echo ' + e.fileName);
			child.stdout.on('data', (data) => {
				vscode.window.showInformationMessage(data);
			});
		});
		context.subscriptions.push(onSave);
	});

	context.subscriptions.push(cmd);
}

And the package file:

{
	"name": "Custom onSave",
	"description": "Execute commands on save.",
	"version": "0.0.1",
	"publisher": "Emeraldwalk",
	"engines": {
		"vscode": "^0.10.1"
	},
	"categories": [
		"Other"
	],
	"activationEvents": [
		"onCommand:extension.executeOnSave"
	],
	"main": "./out/src/extension",
	"contributes": {
		"commands": [{
			"command": "extension.executeOnSave",
			"title": "Execute on Save"
		}]
	},
	"scripts": {
		"vscode:prepublish": "node ./node_modules/vscode/bin/compile",
		"compile": "node ./node_modules/vscode/bin/compile -watch -p ./"
	},
	"devDependencies": {
		"typescript": "^1.6.2",
		"vscode": "0.10.x"
	}
}

The extension is enabled via cmd+shift+p then typing "Execute on Save", but it could be reconfigured to start via another command including "*" which would cause it to load any time VSCode loads.

Once the extension is enabled, the event handler will fire whenever a file is saved (NOTE: this doesn't appear to work when file is first created or on Save as...)

This is just a minor modification of a yo code scaffolded extension as outlined here: https://code.visualstudio.com/docs/extensions/example-hello-world

Update

Here's a Visual Studio Code extension I wrote for running commands on file save. https://marketplace.visualstudio.com/items/emeraldwalk.RunOnSave.

I was using CTRL+S for saving the file manually (this is habitual for me). However, I had a different binding in VS Code that would start with CTRL+S (e.g. swagger extension has a chord where pressing CTRL+S CTRL+W would generate the swagger annotation). This resulted in VS Code waiting for me to press the second chord (CTRL+W) and as such it ignored the save part altogether. I reconfigured all the keybinding chords which had CTRL+S as the first chord to a different combination. After this, pressing CTRL+S formatted my file with gofmt properly.