Ignore commented-out histograms in find_unmapped_histograms.py

tools/metrics/histograms/find_unmapped_histograms.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Scans the Chromium source for histograms that are absent from histograms.xml.
 
 This is a heuristic scan, so a clean run of this script does not guarantee that
 all histograms in the Chromium source are properly mapped.  Notably, field
 trials are entirely ignored by this script.
 
@@ skipping 16 matching lines @@
 C_FILENAME = re.compile(r"""
     .*              # Anything
     \.(cc|cpp|h|mm) # Ending in these extensions
     $               # End of string
     """, re.VERBOSE)
 TEST_FILENAME = re.compile(r"""
     .*   # Anything
     test # The word test
     \.   # A literal '.'
     """, re.VERBOSE)
+NON_NEWLINE = re.compile(r'.+')
 CPP_COMMENT = re.compile(r"""
     \s*             # Optional whitespace
     (?:             # Non-capturing group
         //.*        # C++-style comment
         \n          # Newline
         |           # or
         /\*         # Start C-style comment
         (?:         # Non-capturing group
             (?!\*/) # Negative lookahead for comment end
             [\s\S]  # Any character including newline
@@ skipping 74 matching lines @@
 
 class DirectoryNotFoundException(Exception):
   """Base class to distinguish locally defined exceptions from standard ones."""
   def __init__(self, msg):
     self.msg = msg
 
   def __str__(self):
     return self.msg
 
 
+def keepOnlyNewlines(match_object):
+  """Remove everything from a matched string except for the newline characters.
+  Takes a MatchObject argument so that it can be used directly as the repl
+  argument to re.sub().
+
+  Args:
+    match_object: A MatchObject referencing the string to be substituted, e.g.
+    '  // My histogram\n   '
+
+  Returns:
+     The string with non-newlines removed, eg.
+     '\n'
+  """
+  return NON_NEWLINE.sub('', match_object.group(0))
+
+
 def removeComments(string):
   """Remove any comments from an expression, including leading and trailing
-  whitespace. This does not correctly ignore comments embedded in strings,
-  but that shouldn't matter for this script.
+  whitespace. This does not correctly ignore comments embedded in strings, but
+  that shouldn't matter for this script. Newlines in the removed text are
+  preserved so that line numbers don't change.
 
   Args:
     string: The string to remove comments from, e.g.
     '  // My histogram\n   "My.Important.Counts" '
 
   Returns:
-    The string with comments removed, e.g. '"My.Important.Counts" '
+    The string with comments removed, e.g. '"\nMy.Important.Counts" '
+
   """
-  return CPP_COMMENT.sub('', string)
+  return CPP_COMMENT.sub(keepOnlyNewlines, string)
 
 
 def collapseAdjacentCStrings(string):
   """Collapses any adjacent C strings into a single string.
 
   Useful to re-combine strings that were split across multiple lines to satisfy
   the 80-col restriction.
 
   Args:
     string: The string to recombine, e.g. '"Foo"\n    "bar"'
@@ skipping 70 matching lines @@
                if C_FILENAME.match(f) and not TEST_FILENAME.match(f)]
 
   histograms = set()
   location_map = dict()
   unknown_macros = set()
   all_suffixes = STANDARD_HISTOGRAM_SUFFIXES | STANDARD_LIKE_SUFFIXES
   all_others = OTHER_STANDARD_HISTOGRAMS | OTHER_STANDARD_LIKE_HISTOGRAMS
   for filename in filenames:
     contents = ''
     with open(filename, 'r') as f:
-      contents = f.read()
+      contents = removeComments(f.read())
 
     for match in HISTOGRAM_REGEX.finditer(contents):
       line_number = contents[:match.start()].count('\n') + 1
       if (match.group(2) not in all_suffixes and
           match.group(1) not in all_others):
         full_macro_name = match.group(1)
         if (full_macro_name not in unknown_macros):
           logging.warning('%s:%d: Unknown macro name: <%s>' %
                           (filename, line_number, match.group(1)))
           unknown_macros.add(full_macro_name)
 
         continue
 
-      histogram = removeComments(match.group(3))
+      histogram = match.group(3).strip()
       histogram = collapseAdjacentCStrings(histogram)
 
       # Must begin and end with a quotation mark.
       if not histogram or histogram[0] != '"' or histogram[-1] != '"':
         logNonLiteralHistogram(filename, histogram)
         continue
 
       # Must not include any quotation marks other than at the beginning or end.
       histogram_stripped = histogram.strip('"')
       if '"' in histogram_stripped:
@@ skipping 117 matching lines @@
     logging.warning('No such file: %s', options.extra_histograms_file_location)
 
   if options.output_as_csv:
     output_csv(unmapped_histograms, location_map)
   else:
     output_log(unmapped_histograms, location_map, options.verbose)
 
 
 if __name__ == '__main__':
   main()