Fixed changed goal for BUILD files in build root

Testing Done:
https://travis-ci.org/fkorotkov/pants/builds/78323214 in green

Reviewed at https://rbcommons.com/s/twitter/r/2749/

src/python/pants/backend/core/wrapped_globs.py

@@ -66,7 +66,7 @@ def __init__(self, rel_path):
     self._rel_path = rel_path
 
   def __call__(self, *args, **kwargs):
-    root = os.path.join(get_buildroot(), self._rel_path)
+    root = os.path.normpath(os.path.join(get_buildroot(), self._rel_path))
 
     excludes = kwargs.pop('exclude', [])
     if isinstance(excludes, string_types):
@@ -90,7 +90,7 @@ def files_calculator():
       return result
 
     buildroot = get_buildroot()
-    rel_root = os.path.relpath(root, buildroot)
+    rel_root = os.path.relpath(root, buildroot) if root != buildroot else ''
     filespec = self.to_filespec(args, root=rel_root, excludes=excludes)
     return FilesetWithSpec(rel_root, filespec, files_calculator)
 

tests/python/pants_test/tasks/test_what_changed.py

@@ -13,7 +13,7 @@
 from pants.backend.core.from_target import FromTarget
 from pants.backend.core.targets.resources import Resources
 from pants.backend.core.tasks.what_changed import WhatChanged
-from pants.backend.core.wrapped_globs import RGlobs
+from pants.backend.core.wrapped_globs import RGlobs, Globs
 from pants.backend.jvm.targets.jar_dependency import JarDependency
 from pants.backend.jvm.targets.jar_library import JarLibrary
 from pants.backend.jvm.targets.java_library import JavaLibrary
@@ -42,6 +42,7 @@ def alias_groups(self):
       },
       context_aware_object_factories={
         'source_root': SourceRoot.factory,
+        'globs': Globs.factory,
         'rglobs': RGlobs.factory,
         'from_target': FromTarget,
       },
@@ -201,6 +202,13 @@ def setUp(self):
       )
     """))
 
+    self.add_to_build_file('BUILD.config', dedent("""
+      resources(
+        name='pants-config',
+        sources = globs('pants.ini*')
+      )
+    """))
+
   def test_spec_excludes(self):
     self.assert_console_output(
       'root/src/py/a:alpha',
@@ -361,3 +369,9 @@ def test_deferred_sources(self):
       'root/proto:external-source-jars',
       workspace=self.workspace(files=['root/proto/BUILD'])
     )
+
+  def test_root_config(self):
+    self.assert_console_output(
+      ':pants-config',
+      workspace=self.workspace(files=['pants.ini'])
+    )