rollup/test/sourcemaps/loaders/_config.js

var buble = require( 'buble' );
var fs = require( 'fs' );
var assert = require( 'assert' );
var getLocation = require( '../../utils/getLocation' );
var SourceMapConsumer = require( 'source-map' ).SourceMapConsumer;

module.exports = {
	description: 'preserves sourcemap chains when transforming',
	options: {
		plugins: [
			{
				load: function ( id ) {
					if ( /foo.js$/.test( id ) ) {
						id = id.replace( /foo.js$/, 'bar.js' );
					} else if ( /bar.js$/.test( id ) ) {
						id = id.replace( /bar.js$/, 'foo.js' );
					}

					var code = fs.readFileSync( id, 'utf-8' );

					var out = buble.transform( code, {
						transforms: { modules: false },
						sourceMap: true,
						source: id
					});

					if ( /main.js$/.test( id ) ) {
						delete out.map.sources;
					} else {
						const slash = out.map.sources[0].lastIndexOf( '/' ) + 1;
						out.map.sources = out.map.sources.map( source => '../' + source.slice( slash ) );
						out.map.sourceRoot = 'fake';
					}

					return { code: out.code, map: out.map };
				}
			}
		]
	},
	test: function ( code, map ) {
		var smc = new SourceMapConsumer( map );
		var generatedLoc;
		var originalLoc;

		generatedLoc = getLocation( code, code.indexOf( '22' ) );
		originalLoc = smc.originalPositionFor( generatedLoc );

		assert.equal( originalLoc.source, '../foo.js' );
		assert.equal( originalLoc.line, 1 );
		assert.equal( originalLoc.column, 32 );

		generatedLoc = getLocation( code, code.indexOf( '20' ) );
		originalLoc = smc.originalPositionFor( generatedLoc );

		assert.equal( originalLoc.source, '../bar.js' );
		assert.equal( originalLoc.line, 1 );
		assert.equal( originalLoc.column, 37 );

		generatedLoc = getLocation( code, code.indexOf( 'log' ) );
		originalLoc = smc.originalPositionFor( generatedLoc );

		assert.equal( originalLoc.source, '../main.js' );
		assert.ok( /columns/.test( smc.sourceContentFor( '../main.js' ) ) );
		assert.equal( originalLoc.line, 4 );
		assert.equal( originalLoc.column, 19 );
	}
};