Make sourceRoot resolving more sensible

A source root such as `/scripts/subdir` is not treated as
`/scripts/subdir/` — that is, as a directory called “subdir”, not a file
called “subdir”. Pointing to a file as source root does not makes sense.

lib/source-map-resolve-node.js

@@ -161,13 +161,18 @@ function resolveSourcesSync(map, mapUrl, read) {
   return sources
 }
 
+var endingSlash = /\/?$/
+
 function resolveSourcesHelper(map, mapUrl, fn) {
   mapUrl = urix(mapUrl)
   var fullUrl
   var sourceContent
   for (var index = 0, len = map.sources.length; index < len; index++) {
     if (map.sourceRoot) {
-      fullUrl = resolveUrl(mapUrl, map.sourceRoot, map.sources[index])
+      // Make sure that the sourceRoot ends with a slash, so that `/scripts/subdir` becomes
+      // `/scripts/subdir/<source>`, not `/scripts/<source>`. Pointing to a file as source root
+      // does not make sense.
+      fullUrl = resolveUrl(mapUrl, map.sourceRoot.replace(endingSlash, "/"), map.sources[index])
     } else {
       fullUrl = resolveUrl(mapUrl, map.sources[index])
     }

source-map-resolve.js

@@ -168,12 +168,17 @@ void (function(root, factory) {
     return sources
   }
 
+  var endingSlash = /\/?$/
+
   function resolveSourcesHelper(map, mapUrl, fn) {
     var fullUrl
     var sourceContent
     for (var index = 0, len = map.sources.length; index < len; index++) {
       if (map.sourceRoot) {
-        fullUrl = resolveUrl(mapUrl, map.sourceRoot, map.sources[index])
+        // Make sure that the sourceRoot ends with a slash, so that `/scripts/subdir` becomes
+        // `/scripts/subdir/<source>`, not `/script/<source>`. Pointing to a file as source root
+        // does not make sense.
+        fullUrl = resolveUrl(mapUrl, map.sourceRoot.replace(endingSlash, "/"), map.sources[index])
       } else {
         fullUrl = resolveUrl(mapUrl, map.sources[index])
       }

test/source-map-resolve.js

@@ -29,6 +29,12 @@ var map = {
     sources:    ["foo.js", "lib/bar.js", "../vendor/dom.js", "/version.js", "//foo.org/baz.js"],
     names:      []
   },
+  sourceRootNoSlash: {
+    mappings:   "AAAA",
+    sourceRoot: "/static/js/app",
+    sources:    ["foo.js", "lib/bar.js", "../vendor/dom.js", "/version.js", "//foo.org/baz.js"],
+    names:      []
+  },
   sourceContents: {
     mappings:       "AAAA",
     sourceRoot:     "/static/js/app/",
@@ -270,7 +276,7 @@ function testResolveSources(method, sync) {
 
     var mapUrl = "http://example.com/a/b/c/foo.js.map"
 
-    t.plan(1 + (sync ? 8 : 11) + 5*3 + 4)
+    t.plan(1 + (sync ? 8 : 11) + 6*3 + 4)
 
     t.equal(typeof method, "function", "is a function")
 
@@ -313,6 +319,18 @@ function testResolveSources(method, sync) {
       isAsync()
     })
 
+    method(map.sourceRootNoSlash, mapUrl, wrap(identity), function(error, result) {
+      t.error(error)
+      t.deepEqual(result, [
+        "http://example.com/static/js/app/foo.js",
+        "http://example.com/static/js/app/lib/bar.js",
+        "http://example.com/static/js/vendor/dom.js",
+        "http://example.com/version.js",
+        "http://foo.org/baz.js"
+      ], "sourceRootNoSlash")
+      isAsync()
+    })
+
     method(map.sourceContents, mapUrl, wrap(Throws), function(error, result) {
       t.error(error)
       t.deepEqual(result, [
@@ -375,7 +393,7 @@ function testResolve(method, sync) {
 
     var codeUrl = "http://example.com/a/b/c/foo.js"
 
-    t.plan(1 + (sync ? 7 : 10) + 16*3 + 5*3 + 4)
+    t.plan(1 + (sync ? 7 : 10) + 16*3 + 6*3 + 4)
 
     t.equal(typeof method, "function", "is a function")
 
@@ -581,6 +599,18 @@ function testResolve(method, sync) {
       isAsync()
     })
 
+    method(code.fileRelative, codeUrl, readMap(map.sourceRootNoSlash), function(error, result) {
+      t.error(error)
+      t.deepEqual(result.sources, [
+        "http://example.com/static/js/app/foo.js",
+        "http://example.com/static/js/app/lib/bar.js",
+        "http://example.com/static/js/vendor/dom.js",
+        "http://example.com/version.js",
+        "http://foo.org/baz.js"
+      ], "sourceRootNoSlash")
+      isAsync()
+    })
+
     method(code.fileRelative, codeUrl, readMap(map.sourceContents), function(error, result) {
       t.error(error)
       t.deepEqual(result.sources, [