fix: resolve symbol links until their are no more symbolic links

Depending on your npm / yarn set up a global install may have to resolve
through several symlinks before it correctly arrives the the baseDir
that actually contains the other subcommands.

The changes the resolution logic to resolve symlinks until their are no
more to resolve by using realpath which will resolve links all the way
to the final destination.

index.js

@@ -527,14 +527,11 @@ Command.prototype.executeSubCommand = function(argv, args, unknown) {
 
   // In case of globally installed, get the base dir where executable
   //  subcommand file should be located at
-  var baseDir,
-    link = fs.lstatSync(f).isSymbolicLink() ? fs.readlinkSync(f) : f;
+  var baseDir;
 
-  // when symbolink is relative path
-  if (link !== f && link.charAt(0) !== '/') {
-    link = path.join(dirname(f), link);
-  }
-  baseDir = dirname(link);
+  var resolvedLink = fs.realpathSync(f);
+
+  baseDir = dirname(resolvedLink);
 
   // prefer local `./<bin>` to bin in the $PATH
   var localBin = path.join(baseDir, bin);

test/fixtures/another-dir/pm

@@ -0,0 +1 @@
+../other-dir/pm

test/fixtures/other-dir/pm

@@ -0,0 +1 @@
+../pm

test/test.command.executableSubcommand.js

@@ -34,3 +34,10 @@ var bin = path.join(__dirname, './fixtures/pmlink')
 exec(bin + ' install', function (error, stdout, stderr) {
   stdout.should.equal('install\n');
 });
+
+// when `bin` is a symbol link pointing at a symbolic for mocking global install
+var bin = path.join(__dirname, './fixtures/another-dir/pm')
+// success case
+exec(bin + ' install', function (error, stdout, stderr) {
+  stdout.should.equal('install\n');
+});

test/test.command.executableSubcommandAlias.js

@@ -26,3 +26,10 @@ var bin = path.join(__dirname, './fixtures/pmlink')
 exec(bin + ' i', function (error, stdout, stderr) {
   stdout.should.equal('install\n');
 });
+
+// when `bin` is a symbol link pointing at a symbolic for mocking global install
+var bin = path.join(__dirname, './fixtures/another-dir/pm')
+// success case
+exec(bin + ' install', function (error, stdout, stderr) {
+  stdout.should.equal('install\n');
+});

test/test.command.executableSubcommandDefault.js

@@ -44,3 +44,10 @@ var bin = path.join(__dirname, './fixtures/pmlink')
 exec(bin + ' install', function (error, stdout, stderr) {
   stdout.should.equal('install\n');
 });
+
+// when `bin` is a symbol link pointing at a symbolic for mocking global install
+var bin = path.join(__dirname, './fixtures/another-dir/pm')
+// success case
+exec(bin + ' install', function (error, stdout, stderr) {
+  stdout.should.equal('install\n');
+});