Implement 'negate' to simplify pcre

pre_commit/languages/pcre.py

@@ -2,7 +2,6 @@ from __future__ import unicode_literals
 
 from sys import platform
 
-from pre_commit.util import shell_escape
 from pre_commit.xargs import xargs
 
 
@@ -19,21 +18,12 @@ def install_environment(
 
 
 def run_hook(repo_cmd_runner, hook, file_args):
-    grep_command = '{0} -H -n -P'.format(
-        'ggrep' if platform == 'darwin' else 'grep',
-    )
-
     # For PCRE the entry is the regular expression to match
-    return xargs(
-        (
-            'sh', '-c',
-            # Grep usually returns 0 for matches, and nonzero for non-matches
-            # so we flip it here.
-            '! {0} {1} {2} $@'.format(
-                grep_command, ' '.join(hook['args']),
-                shell_escape(hook['entry']),
-            ),
-            '--',
-        ),
-        file_args,
-    )
+    cmd = (
+        'ggrep' if platform == 'darwin' else 'grep',
+        '-H', '-n', '-P',
+    ) + tuple(hook['args']) + (hook['entry'],)
+
+    # Grep usually returns 0 for matches, and nonzero for non-matches so we
+    # negate it here.
+    return xargs(cmd, file_args, negate=True)

pre_commit/util.py

@@ -67,10 +67,6 @@ def noop_context():
     yield
 
 
-def shell_escape(arg):
-    return "'" + arg.replace("'", "'\"'\"'".strip()) + "'"
-
-
 def no_git_env():
     # Too many bugs dealing with environment variables and GIT:
     # https://github.com/pre-commit/pre-commit/issues/300

pre_commit/xargs.py

@@ -42,17 +42,31 @@ def partition(cmd, varargs, _max_length=MAX_LENGTH):
     return tuple(ret)
 
 
-def xargs(cmd, varargs):
-    """A simplified implementation of xargs."""
+def xargs(cmd, varargs, **kwargs):
+    """A simplified implementation of xargs.
+
+    negate: Make nonzero successful and zero a failure
+    """
+    negate = kwargs.pop('negate', False)
     retcode = 0
     stdout = b''
     stderr = b''
 
-    for run_cmd in partition(cmd, varargs):
+    for run_cmd in partition(cmd, varargs, **kwargs):
         proc_retcode, proc_out, proc_err = cmd_output(
             *run_cmd, encoding=None, retcode=None
         )
-        retcode |= proc_retcode
+        # This is *slightly* too clever so I'll explain it.
+        # First the xor boolean table:
+        #     T | F |
+        #   +-------+
+        # T | F | T |
+        # --+-------+
+        # F | T | F |
+        # --+-------+
+        # When negate is True, it has the effect of flipping the return code
+        # Otherwise, the retuncode is unchanged
+        retcode |= bool(proc_retcode) ^ negate
         stdout += proc_out
         stderr += proc_err