Add --quiet command line argument

Quiet makes output quiet unless errors occurs.

Mainly used by automation tools when parsing huge amount of files.
In those cases actual error might get lost in the pile of other stats
prints.

This argument is also handy for build system integration, so it's
possible to add automated lint target to a project and invoke it
via build system and have no pollution of terminals or IDE.

For example when hooking cmakelint to a Ninja project without this
argument one will have screen filled with "Total Errors: 0" messages,
which defeats all the idea of clean Ninja output.

cpplint/cpplint.py

@@ -56,7 +56,7 @@ import unicodedata
 _USAGE = """
 Syntax: cpplint.py [--verbose=#] [--output=vs7] [--filter=-x,+y,...]
                    [--counting=total|toplevel|detailed] [--root=subdir]
-                   [--linelength=digits]
+                   [--linelength=digits] [--quiet]
         <file> [file] ...
 
   The style guidelines this tries to follow are those in
@@ -128,6 +128,15 @@ Syntax: cpplint.py [--verbose=#] [--output=vs7] [--filter=-x,+y,...]
       Examples:
         --linelength=120
 
+    quiet makes output quiet unless errors occurs
+      Mainly used by automation tools when parsing huge amount of files.
+      In those cases actual error might get lost in the pile of other stats
+      prints.
+
+      This argument is also handy for build system integration, so it's
+      possible to add automated lint target to a project and invoke it
+      via build system and have no pollution of terminals or IDE.
+
     extensions=extension,extension,...
       The allowed file extensions that cpplint will check
 
@@ -143,6 +152,7 @@ Syntax: cpplint.py [--verbose=#] [--output=vs7] [--filter=-x,+y,...]
       exclude_files=regex
       linelength=80
       root=subdir
+      quiet
 
     "set noparent" option prevents cpplint from traversing directory tree
     upwards looking for more .cfg files in parent directories. This option
@@ -161,6 +171,8 @@ Syntax: cpplint.py [--verbose=#] [--output=vs7] [--filter=-x,+y,...]
     The "root" option is similar in function to the --root flag (see example
     above).
 
+    The "quiet" option is similar in function to the --quiet.
+
     CPPLINT.cfg has an effect on files in the same directory and all
     sub-directories, unless overridden by a nested configuration file.
 
@@ -532,6 +544,9 @@ _root = None
 # This is set by --linelength flag.
 _line_length = 80
 
+# Supress messages unless error occurs.
+_quiet = False
+
 # The allowed extensions for file names
 # This is set by --extensions flag.
 _valid_extensions = set(['cc', 'h', 'cpp', 'cu', 'cuh'])
@@ -909,7 +924,8 @@ class _CppLintState(object):
     for category, count in self.errors_by_category.iteritems():
       sys.stderr.write('Category \'%s\' errors found: %d\n' %
                        (category, count))
-    sys.stderr.write('Total errors found: %d\n' % self.error_count)
+    if self.error_count > 0 or not _quiet:
+      sys.stderr.write('Total errors found: %d\n' % self.error_count)
 
 _cpplint_state = _CppLintState()
 
@@ -5893,6 +5909,8 @@ def ProcessConfigOverrides(filename):
           elif name == 'root':
             global _root
             _root = val
+          elif name == 'quiet':
+            _quiet = True
           else:
             sys.stderr.write(
                 'Invalid configuration option (%s) in file %s\n' %
@@ -5995,7 +6013,8 @@ def ProcessFile(filename, vlevel, extra_check_functions=[]):
         Error(filename, linenum, 'whitespace/newline', 1,
               'Unexpected \\r (^M) found; better to use only \\n')
 
-  sys.stderr.write('Done processing %s\n' % filename)
+  if not _quiet:
+    sys.stderr.write('Done processing %s\n' % filename)
   _RestoreFilters()
 
 
@@ -6038,7 +6057,7 @@ def ParseArguments(args):
                                                  'filter=',
                                                  'root=',
                                                  'linelength=',
-                                                 'extensions='])
+                                                 'extensions=', 'quiet'])
   except getopt.GetoptError:
     PrintUsage('Invalid arguments.')
 
@@ -6079,6 +6098,9 @@ def ParseArguments(args):
           _valid_extensions = set(val.split(','))
       except ValueError:
           PrintUsage('Extensions must be comma seperated list.')
+    elif opt == '--quiet':
+      global _quiet
+      _quiet = True
 
   if not filenames:
     PrintUsage('No files were specified.')