📦 NEW: Providing warning on invalid block name — FIX #28 (#40)

Add regex checking whether block name is valid or not and a function that logs an error message to user

```
⚠️ A block name must begin with a letter.
⚠️ A block name can only contain lowercase alphanumeric characters and dashes.
```

* 📦 NEW: Invalid Block name info

* 🐛 FIX: Inline docs

Author: lukekowalski

packages/create-guten-block/app/cli.js

@@ -10,6 +10,7 @@ const chalk = require( 'chalk' );
 const commander = require( 'commander' );
 const maybeEnvInfo = require( './envInfo' );
 const noBlockName = require( './noBlockName' );
+const invalidBlockName = require( './invalidBlockName' );
 const packageJson = require( '../package.json' );
 
 // Commander.js program.
@@ -53,5 +54,11 @@ module.exports = () => {
 		.split( ' ' )
 		.join( '-' );
 
+	// Check if block name is valid.
+	const blockNameRegex = /^[a-z][a-z0-9-]/;
+	if ( ! blockNameRegex.test( formatBlockName ) ) {
+		invalidBlockName();
+	}
+
 	return formatBlockName;
 };

packages/create-guten-block/app/invalidBlockName.js

@@ -0,0 +1,23 @@
+/**
+ * Handle if there's block name is not valid.
+ */
+
+'use strict';
+
+const chalk = require( 'chalk' );
+
+module.exports = () => {
+	// Stop if given block name is not valid.
+	console.log(
+		'\n❌ ',
+		chalk.black.bgRed( ' Please provide a valid block name: \n' )
+	);
+	console.log(
+		`${ chalk.dim(
+			'⚠️  A block name can only contain lowercase alphanumeric characters and dashes.'
+		) }`
+	);
+	console.log( `${ chalk.dim( '⚠️  A block name must begin with a letter.' ) }` );
+	console.log();
+	process.exit( 1 );
+};