Add options for file type in lister.py

Add option to filter files by their extension.
Add option to return a dict of list of files keyed by their file type.

tools/lister.py

@@ -3,17 +3,32 @@ from __future__ import print_function
 
 import os
 import subprocess
+from collections import defaultdict
 
-def list_files(targets=[], modified_only=False, exclude=[]):
+def get_ftype(fpath):
+    ext = os.path.splitext(fpath)[1]
+    if ext:
+        return ext[1:]
+    else:
+        return ''
+
+def list_files(targets=[], ftypes=[], modified_only=False, exclude=[], group_by_ftype=False):
     """
     List files tracked by git.
     Returns a list of files which are either in targets or in directories in targets.
     If targets is [], list of all tracked files in current directory is returned.
 
     Other arguments:
+    ftypes - List of file types on which to filter the search.
+        If ftypes is [], all files are included.
     modified_only - Only include files which have been modified.
     exclude - List of paths to be excluded.
+    group_by_ftype - If True, returns a dict of lists keyed by file type.
+        If False, returns a flat list of files.
     """
+    ftypes = [x.strip('.') for x in ftypes]
+    ftypes_set = set(ftypes)
+
     cmdline = ['git', 'ls-files'] + targets
     if modified_only:
         cmdline.append('-m')
@@ -22,7 +37,7 @@ def list_files(targets=[], modified_only=False, exclude=[]):
     # throw away empty lines and non-files (like symlinks)
     files = list(filter(os.path.isfile, files_gen))
 
-    result = []
+    result = defaultdict(list) if group_by_ftype else []
 
     for fpath in files:
         # this will take a long time if exclude is very large
@@ -34,6 +49,14 @@ def list_files(targets=[], modified_only=False, exclude=[]):
         if in_exclude:
             continue
 
+        if ftypes or group_by_ftype:
+            filetype = get_ftype(fpath)
+            if ftypes and filetype not in ftypes_set:
+                continue
+
+        if group_by_ftype:
+            result['.' + filetype].append(fpath)
+        else:
             result.append(fpath)
 
     return result