Fix in-memory sourcemap filename

src/Chunk.ts

@@ -1042,8 +1042,10 @@ export default class Chunk {
 				if (options.sourcemap) {
 					timeStart('sourcemap', 3);
 
-					let file = options.file ? options.sourcemapFile || options.file : this.id;
-					if (file) file = resolve(typeof process !== 'undefined' ? process.cwd() : '', file);
+					let file: string;
+					if (options.file) file = resolve(options.sourcemapFile || options.file);
+					else if (options.dir) file = resolve(options.dir, this.id);
+					else file = resolve(this.id);
 
 					if (
 						this.graph.hasLoaders ||

src/rollup/index.ts

@@ -1,5 +1,5 @@
 import { getTimings, initialiseTimers, timeEnd, timeStart } from '../utils/timers';
-import { basename } from '../utils/path';
+import { basename, resolve, dirname, relative } from '../utils/path';
 import { writeFile } from '../utils/fs';
 import { mapSequence } from '../utils/promise';
 import error from '../utils/error';
@@ -169,6 +169,10 @@ export default function rollup(
 						.then(addons => {
 							chunk.generateInternalExports(outputOptions);
 							chunk.preRender(outputOptions);
+							chunk.id =
+								typeof process !== 'undefined'
+									? relative(process.cwd(), inputOptions.input)
+									: inputOptions.input;
 							return chunk.render(outputOptions, addons);
 						})
 						.then(rendered => {
@@ -312,6 +316,12 @@ export default function rollup(
 						});
 					}
 
+					if (outputOptions.sourcemapFile)
+						error({
+							code: 'INVALID_OPTION',
+							message: '"sourcemapFile" is only supported for single-file builds.'
+						});
+
 					timeStart('GENERATE', 1);
 
 					const generated: { [chunkName: string]: OutputChunk } = {};

test/misc/index.js

@@ -1,6 +1,9 @@
 const assert = require('assert');
+const path = require('path');
 const rollup = require('../../dist/rollup');
 const { executeBundle, loader } = require('../utils.js');
+const { SourceMapConsumer } = require( 'source-map' );
+const { getLocator } = require( 'locate-character' );
 
 describe('sanity checks', () => {
 	it('exists', () => {
@@ -158,6 +161,33 @@ describe('sanity checks', () => {
 	});
 });
 
+describe('in-memory sourcemaps', () => {
+	it( 'generates an in-memory sourcemap', () => {
+		return rollup.rollup({
+			input: 'main',
+			plugins: [loader({ main: `console.log( 42 );` })],
+		})
+		.then(bundle => {
+			return bundle.generate({
+				format: 'cjs',
+				sourcemap: true,
+				sourcemapFile: path.resolve( 'bundle.js' )
+			});
+		})
+		.then(generated => {
+			const smc = new SourceMapConsumer( generated.map );
+			const locator = getLocator( generated.code, { offsetLine: 1 });
+
+			let generatedLoc = locator( '42' );
+			let loc = smc.originalPositionFor( generatedLoc ); // 42
+			assert.equal( loc.source, 'main' );
+			assert.equal( loc.line, 1 );
+			assert.equal( loc.column, 13 );
+		});
+	});
+
+});
+
 describe('deprecations', () => {
 	it('warns on options.entry, but handles', () => {
 		const warnings = [];