Ensure source maps contain relative paths

Fixes #1882.

Author: novemberborn

lib/babel-pipeline.js

@@ -145,7 +145,9 @@ function build(projectDir, cacheDir, userOptions, compileEnhancements) {
 			cwd: projectDir,
 			envName,
 			inputSourceMap,
-			filename
+			filename,
+			sourceFileName: path.relative(projectDir, filename),
+			sourceRoot: projectDir
 		}));
 
 		// TODO: Check for `partialTestConfig.config` and include a hash of the file

test/fixture/correct-sources-in-source-map/package.json

@@ -0,0 +1 @@
+{}

test/fixture/correct-sources-in-source-map/test/path-to/the/test-file.js

@@ -0,0 +1,3 @@
+import test from '../../../../../..';
+
+test('ok', t => t.pass());

test/integration/babel.js

@@ -1,4 +1,7 @@
 'use strict';
+const fs = require('fs');
+const path = require('path');
+const globby = require('globby');
 const test = require('tap').test;
 const figures = require('figures');
 const pkg = require('../../package.json');
@@ -30,3 +33,16 @@ for (const which of [
 		});
 	});
 }
+
+test('includes relative paths in source map', t => {
+	execCli([], {dirname: 'fixture/correct-sources-in-source-map'}, () => {
+		const [file] = globby.sync(['*.js.map'], {
+			absolute: true,
+			cwd: path.resolve(__dirname, '../fixture/correct-sources-in-source-map/node_modules/.cache/ava')
+		});
+		const map = JSON.parse(fs.readFileSync(file, 'utf8'));
+		t.same(map.sources, [path.normalize('test/path-to/the/test-file.js')]);
+		t.is(map.sourceRoot, path.resolve(__dirname, '../fixture/correct-sources-in-source-map'));
+		t.end();
+	});
+});