Add option to determine file type in lister.py using shebang.

tools/lister.py

@@ -2,17 +2,35 @@
 from __future__ import print_function
 
 import os
+import sys
 import subprocess
+import re
 from collections import defaultdict
 
-def get_ftype(fpath):
+def get_ftype(fpath, use_shebang):
     ext = os.path.splitext(fpath)[1]
     if ext:
         return ext[1:]
+    elif use_shebang:
+        # opening a file may throw an OSError
+        with open(fpath) as f:
+            first_line = f.readline()
+            if re.search(r'^#!.*\bpython', first_line):
+                return 'py'
+            elif re.search(r'^#!.*sh', first_line):
+                return 'sh'
+            elif re.search(r'^#!.*\bperl', first_line):
+                return 'pl'
+            elif re.search(r'^#!', first_line):
+                print('Error: Unknown shebang in file "%s":\n%s' % (fpath, first_line), file=sys.stderr)
+                return ''
+            else:
+                return ''
     else:
         return ''
 
-def list_files(targets=[], ftypes=[], modified_only=False, exclude=[], group_by_ftype=False):
+def list_files(targets=[], ftypes=[], use_shebang=True, 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.
@@ -21,6 +39,7 @@ def list_files(targets=[], ftypes=[], modified_only=False, exclude=[], group_by_
     Other arguments:
     ftypes - List of file types on which to filter the search.
         If ftypes is [], all files are included.
+    use_shebang - Determine file type of extensionless files from their shebang.
     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.
@@ -50,7 +69,13 @@ def list_files(targets=[], ftypes=[], modified_only=False, exclude=[], group_by_
             continue
 
         if ftypes or group_by_ftype:
-            filetype = get_ftype(fpath)
+            try:
+                filetype = get_ftype(fpath, use_shebang)
+            except (OSError, UnicodeDecodeError) as e:
+                etype = e.__class__.__name__
+                print('Error: %s while determining type of file "%s":' % (etype, fpath), file=sys.stderr)
+                print(e, file=sys.stderr)
+                filetype = ''
             if ftypes and filetype not in ftypes_set:
                 continue