fix options.sourceFileName gennerate bug (#260)

* improve sourceFileName gennerate logic with new relative method

* add test for relative method

src/index.js

@@ -4,6 +4,7 @@ const loaderUtils = require("loader-utils");
 const path = require("path");
 const cache = require("./fs-cache.js");
 const exists = require("./utils/exists")();
+const relative = require("./utils/relative");
 const read = require("./utils/read")();
 const resolveRc = require("./resolve-rc.js");
 const pkg = require("./../package.json");
@@ -98,9 +99,9 @@ module.exports = function(source, inputSourceMap) {
   }
 
   if (options.sourceFileName === undefined) {
-    options.sourceFileName = path.relative(
-        options.sourceRoot,
-        options.filename
+    options.sourceFileName = relative(
+      options.sourceRoot,
+      options.filename
     );
   }
 

src/utils/relative.js

@@ -0,0 +1,39 @@
+/**
+* Make a path relative to a URL or another path.
+* Borrowed from https://github.com/mozilla/source-map/blob/master/lib/util.js
+*
+* @param aRoot The root path or URL.
+* @param aPath The path or URL to be made relative to aRoot.
+*/
+module.exports = function relative(aRoot, aPath) {
+  if (aRoot === "") {
+    aRoot = ".";
+  }
+
+  aRoot = aRoot.replace(/\/$/, "");
+
+  // It is possible for the path to be above the root. In this case, simply
+  // checking whether the root is a prefix of the path won't work. Instead, we
+  // need to remove components from the root one by one, until either we find
+  // a prefix that fits, or we run out of components to remove.
+  let level = 0;
+  while (aPath.indexOf(aRoot + "/") !== 0) {
+    const index = aRoot.lastIndexOf("/");
+    if (index < 0) {
+      return aPath;
+    }
+
+    // If the only part of the root that is left is the scheme (i.e. http://,
+    // file:///, etc.), one or more slashes (/), or simply nothing at all, we
+    // have exhausted all components, so the path is not relative to the root.
+    aRoot = aRoot.slice(0, index);
+    if (aRoot.match(/^([^\/]+:\/)?\/*$/)) {
+      return aPath;
+    }
+
+    ++level;
+  }
+
+  // Make sure we add a '../' for each component we removed from the root.
+  return Array(level + 1).join("../") + aPath.substr(aRoot.length + 1);
+};

test/utils/relative.test.js

@@ -0,0 +1,16 @@
+import test from "ava";
+import relative from "../../lib/utils/relative.js";
+
+test("should get correct relative path", (t) => {
+  t.is(relative("/the/root", "/the/root/one.js"), "one.js");
+  t.is(relative("/the/root", "/the/rootone.js"), "../rootone.js");
+  t.is(relative("/the/root", "/therootone.js"), "/therootone.js");
+
+  t.is(relative("", "/the/root/one.js"), "/the/root/one.js");
+  t.is(relative(".", "/the/root/one.js"), "/the/root/one.js");
+  t.is(relative("", "the/root/one.js"), "the/root/one.js");
+  t.is(relative(".", "the/root/one.js"), "the/root/one.js");
+
+  t.is(relative("/", "/the/root/one.js"), "the/root/one.js");
+  t.is(relative("/", "the/root/one.js"), "the/root/one.js");
+});