Support source map pragmas for stack traces

When using source maps to compute stack traces, if the source map is not in
memory, fall back to source-map-support's default retrieval function which can
get it from a source map pragma in the source file.

This means any dependency that has such pragmas (and the required map files) has
its errors mapped correctly, e.g. the code under test, or third-party
dependencies that ship with source maps.

This should also work for inline source maps, though no test case was included.

Author: novemberborn

lib/babel.js

@@ -1,15 +1,16 @@
 'use strict';
 var sourceMapCache = Object.create(null);
 
-require('source-map-support').install({
+var sourceMapSupport = require('source-map-support');
+sourceMapSupport.install({
 	retrieveSourceMap: function (source) {
 		if (sourceMapCache[source]) {
 			return {
 				url: source,
 				map: sourceMapCache[source]
 			};
 		}
-		return null;
+		return sourceMapSupport.retrieveSourceMap(source);
 	}
 });
 

test/cli.js

@@ -202,6 +202,16 @@ test('stack traces for exceptions are corrected using a source map', function (t
 	});
 });
 
+test('stack traces for exceptions are corrected using a source map, found via a pragma', function (t) {
+	execCli('fixture/source-map-pragma-exception.js', function (err, stdout, stderr) {
+		t.ok(err);
+		t.true(/Can't catch me!/.test(stderr));
+		t.match(stderr, /^.*?at.*?bar\b.*source-with-source-map-pragma.js:8.*$/m);
+		t.match(stderr, /^.*?at.*?foo\b.*source-with-source-map-pragma.js:4.*$/m);
+		t.end();
+	});
+});
+
 test('absolute paths in CLI', function (t) {
 	t.plan(2);
 

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

@@ -0,0 +1,6 @@
+const test = require('../../');
+const foo = require('./source-with-source-map-pragma');
+
+test('throw an uncaught exception', t => {
+	setImmediate(foo);
+});

test/fixture/source-with-source-map-pragma.js

@@ -0,0 +1,25 @@
+"use strict";
+
+module.exports = foo;
+
+function foo() {
+	bar();
+}
+
+function bar() {
+	throw new Error("Can't catch me!");
+}
+
+//# sourceMappingURL=./source-with-source-map-pragma.map
+
+/* original source:
+module.exports = foo
+
+function foo() {
+	bar()
+}
+
+function bar() {
+	throw new Error(`Can't catch me!`)
+}
+*/