mixins: moved debug logs to 'filter_file'. Renamed shadowed variable name.

Following comments from Todd:

- the call to tty.debug has been moved deeper, to log the filtering of each file
- the shadowing on the name "kwargs" is avoided

lib/spack/llnl/util/filesystem.py

@@ -119,9 +119,15 @@ def groupid_to_group(x):
         regex = re.escape(regex)
 
     for filename in filenames:
+
+        msg = 'FILTER FILE: {0} [replacing "{1}"]'
+        tty.debug(msg.format(filename, regex))
+
         backup_filename = filename + "~"
 
         if ignore_absent and not os.path.exists(filename):
+            msg = 'FILTER FILE: file "{0}" not found. Skipping to next file.'
+            tty.debug(msg.format(filename))
             continue
 
         # Create backup file. Don't overwrite an existing backup

lib/spack/spack/mixins.py

@@ -29,8 +29,6 @@
 import os
 
 import llnl.util.filesystem
-import llnl.util.tty as tty
-
 
 __all__ = [
     'filter_compiler_wrappers'
@@ -152,25 +150,26 @@ def filter_compiler_wrappers(*files, **kwargs):
     after = kwargs.get('after', 'install')
 
     def _filter_compiler_wrappers_impl(self):
-
-        tty.debug('Filtering compiler wrappers: {0}'.format(files))
-
         # Compute the absolute path of the files to be filtered and
         # remove links from the list.
         abs_files = llnl.util.filesystem.find(self.prefix, files)
         abs_files = [x for x in abs_files if not os.path.islink(x)]
 
-        kwargs = {'ignore_absent': True, 'backup': False, 'string': True}
+        filter_kwargs = {
+            'ignore_absent': True,
+            'backup': False,
+            'string': True
+        }
 
         x = llnl.util.filesystem.FileFilter(*abs_files)
 
-        x.filter(os.environ['CC'], self.compiler.cc, **kwargs)
-        x.filter(os.environ['CXX'], self.compiler.cxx, **kwargs)
-        x.filter(os.environ['F77'], self.compiler.f77, **kwargs)
-        x.filter(os.environ['FC'], self.compiler.fc, **kwargs)
+        x.filter(os.environ['CC'], self.compiler.cc, **filter_kwargs)
+        x.filter(os.environ['CXX'], self.compiler.cxx, **filter_kwargs)
+        x.filter(os.environ['F77'], self.compiler.f77, **filter_kwargs)
+        x.filter(os.environ['FC'], self.compiler.fc, **filter_kwargs)
 
         # Remove this linking flag if present (it turns RPATH into RUNPATH)
-        x.filter('-Wl,--enable-new-dtags', '', **kwargs)
+        x.filter('-Wl,--enable-new-dtags', '', **filter_kwargs)
 
     PackageMixinsMeta.register_method_after(
         _filter_compiler_wrappers_impl, after