richer warnings in CLI

bin/src/runRollup.js

@@ -1,7 +1,9 @@
 import { realpathSync } from 'fs';
 import * as rollup from 'rollup';
 import relative from 'require-relative';
+import * as chalk from 'chalk';
 import handleError from './handleError';
+import relativeId from '../../src/utils/relativeId.js';
 import SOURCEMAPPING_URL from './sourceMappingUrl.js';
 
 import { install as installSourcemapSupport } from 'source-map-support';
@@ -143,7 +145,32 @@ function execute ( options, command ) {
 		external = ( optionsExternal || [] ).concat( commandExternal );
 	}
 
-	options.onwarn = options.onwarn || ( warning => stderr( warning.toString() ) );
+	if ( !options.onwarn ) {
+		const seen = new Set();
+
+		options.onwarn = warning => {
+			const str = warning.toString();
+
+			if ( seen.has( str ) ) return;
+			seen.add( str );
+
+			stderr( `⚠️   ${chalk.bold( warning.message )}` );
+
+			if ( warning.url ) {
+				stderr( chalk.cyan( warning.url ) );
+			}
+
+			if ( warning.loc ) {
+				stderr( `${relativeId( warning.loc.file )} (${warning.loc.line}:${warning.loc.column})` );
+			}
+
+			if ( warning.frame ) {
+				stderr( chalk.dim( warning.frame ) );
+			}
+
+			stderr( '' );
+		};
+	}
 
 	options.external = external;
 

rollup.config.cli.js

@@ -15,7 +15,9 @@ export default {
 		buble(),
 		commonjs({
 			include: 'node_modules/**',
-			namedExports: { chalk: [ 'red', 'cyan', 'grey' ] }
+			namedExports: {
+				chalk: [ 'yellow', 'red', 'cyan', 'grey', 'dim', 'bold' ]
+			}
 		}),
 		nodeResolve({
 			main: true

src/Bundle.js

@@ -588,7 +588,7 @@ export default class Bundle {
 	warn ( warning ) {
 		warning.toString = () => {
 			if ( warning.loc ) {
-				return `${warning.loc.file} (${warning.loc.line}:${warning.loc.column}) ${warning.message}`;
+				return `${relativeId( warning.loc.file )} (${warning.loc.line}:${warning.loc.column}) ${warning.message}`;
 			}
 
 			return warning.message;