Bug 1365414 - Update eslint-plugin-mozilla to also search for MC root from CWD. r=standard8

The eslint-plugin-mozilla currently searches for Mozilla Central root by
walking up from its installed dir. However, if the plugin is installed outside
of central, such as globally, it will not find the root. This changeset
retains that behaviour, but will also perform the same check from the current
working directly before failing.

MozReview-Commit-ID: 2L3JqLTuVDS

--HG--
extra : rebase_source : e24ddc726cb2470f7165f028f71416e942c44f87

tools/lint/eslint/eslint-plugin-mozilla/lib/helpers.js

@@ -520,26 +520,35 @@ module.exports = {
 
   /**
    * Gets the root directory of the repository by walking up directories from
-   * this file until a .eslintignore file is found.
+   * this file until a .eslintignore file is found. If this fails, the same
+   * procedure will be attempted from the current working dir.
    * @return {String} The absolute path of the repository directory
    */
   get rootDir() {
     if (!gRootDir) {
-      let dirName = path.dirname(module.filename);
-
-      while (true) {
-        const parsed = path.parse(dirName);
-        if (parsed.root === dirName) {
-          // We've reached the top of the filesystem
-          throw new Error("Unable to find root of repository");
+      function searchUpForIgnore(dirName) {
+        let parsed = path.parse(dirName);
+        while (parsed.root !== dirName) {
+          if (fs.existsSync(path.join(dirName, ".eslintignore"))) {
+            return dirName;
+          }
+          // Move up a level
+          dirName = parsed.dir;
+          parsed = path.parse(dirName);
         }
-        dirName = parsed.dir;
-        if (fs.existsSync(path.join(dirName, ".eslintignore"))) {
-          break;
+        return null;
+      }
+
+      let possibleRoot = searchUpForIgnore(path.dirname(module.filename));
+      if (!possibleRoot) {
+        possibleRoot = searchUpForIgnore(path.resolve());
+        if (!possibleRoot) {
+          // We've couldn't find a root from the module or CWD
+          throw new Error("Unable to find root of repository");
         }
       }
 
-      gRootDir = dirName;
+      gRootDir = possibleRoot;
     }
 
     return gRootDir;