Stack traces for input source maps

lib/babel.js

@@ -48,7 +48,8 @@ var options = {
 	blacklist: hasGenerator ? ['regenerator'] : [],
 	optional: hasGenerator ? ['asyncToGenerator', 'runtime'] : ['runtime'],
 	plugins: [powerAssert],
-	sourceMaps: true
+	sourceMaps: true,
+	inputSourceMap: null
 };
 
 // check if test files required ava and show error, when they didn't
@@ -58,9 +59,18 @@ process.on('uncaughtException', function (exception) {
 	send('uncaughtException', {exception: serializeError(exception)});
 });
 
+// try to load an input source map for the test file, in case the file was
+// already compiled once by the user
+var inputSourceMap = sourceMapSupport.retrieveSourceMap(testPath);
+if (inputSourceMap) {
+	// source-map-support returns the source map as a json-encoded string, but
+	// babel requires an actual object
+	options.inputSourceMap = JSON.parse(inputSourceMap.map);
+}
+
 // include test file
 var transpiled = babel.transformFileSync(testPath, options);
-sourceMapCache[testPath] = JSON.stringify(transpiled.map);
+sourceMapCache[testPath] = transpiled.map;
 requireFromString(transpiled.code, testPath, {
 	appendPaths: module.paths
 });

test/cli.js

@@ -205,6 +205,16 @@ test('stack traces for exceptions are corrected using a source map', function (t
 	});
 });
 
+test('stack traces for exceptions are corrected using a source map, taking an initial source map for the test file into account', function (t) {
+	execCli('fixture/initial-source-map-exception.js', function (err, stdout, stderr) {
+		t.ok(err);
+		t.true(/Can't catch me!/.test(stderr));
+		t.match(stderr, /^.*?at.*?bar\b.*initial-source-map-exception.js:12.*$/m);
+		t.match(stderr, /^.*?at.*?foo\b.*initial-source-map-exception.js:8.*$/m);
+		t.end();
+	});
+});
+
 test('stack traces for exceptions are corrected using a source map, found via a pragma', function (t) {
 	execCli('fixture/source-map-pragma-exception.js', function (err, stdout, stderr) {
 		t.ok(err);

test/fixture/initial-source-map-exception.js

@@ -0,0 +1,33 @@
+'use strict';
+
+var test = require('../../');
+
+test('throw an uncaught exception', function (t) {
+	setImmediate(foo);
+});
+
+function foo() {
+	bar();
+}
+
+function bar() {
+	throw new Error('Can\'t catch me!');
+}
+
+//# sourceMappingURL=./initial-source-map-exception.map
+
+/* original source:
+const test = require('../../');
+
+test('throw an uncaught exception', t => {
+	setImmediate(foo);
+});
+
+function foo() {
+	bar();
+}
+
+function bar() {
+	throw new Error(`Can't catch me!`)
+}
+*/