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(
+    cmd = (
-        (
+        'ggrep' if platform == 'darwin' else 'grep',
-            'sh', '-c',
+        '-H', '-n', '-P',
-            # Grep usually returns 0 for matches, and nonzero for non-matches
+    ) + tuple(hook['args']) + (hook['entry'],)
-            # so we flip it here.
+
-            '! {0} {1} {2} $@'.format(
+    # Grep usually returns 0 for matches, and nonzero for non-matches so we
-                grep_command, ' '.join(hook['args']),
+    # negate it here.
-                shell_escape(hook['entry']),
+    return xargs(cmd, file_args, negate=True)
-            ),
-            '--',
-        ),
-        file_args,
-    )

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):
+def xargs(cmd, varargs, **kwargs):
-    """A simplified implementation of xargs."""
+    """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
 

tests/util_test.py

@@ -9,7 +9,6 @@ import pytest
 from pre_commit.util import clean_path_on_failure
 from pre_commit.util import cwd
 from pre_commit.util import memoize_by_cwd
-from pre_commit.util import shell_escape
 from pre_commit.util import tmpdir
 
 
@@ -79,18 +78,6 @@ def test_clean_path_on_failure_cleans_for_system_exit(in_tmpdir):
     assert not os.path.exists('foo')
 
 
-@pytest.mark.parametrize(
-    ('input_str', 'expected'),
-    (
-        ('', "''"),
-        ('foo"bar', "'foo\"bar'"),
-        ("foo'bar", "'foo'\"'\"'bar'")
-    ),
-)
-def test_shell_escape(input_str, expected):
-    assert shell_escape(input_str) == expected
-
-
 def test_tmpdir():
     with tmpdir() as tempdir:
         assert os.path.exists(tempdir)

tests/xargs_test.py

@@ -45,3 +45,28 @@ def test_xargs_smoke():
     assert ret == 0
     assert out == b'hello world\n'
     assert err == b''
+
+
+exit_cmd = ('bash', '-c', 'exit $1', '--')
+# Abuse max_length to control the exit code
+max_length = len(' '.join(exit_cmd)) + 2
+
+
+def test_xargs_negate():
+    ret, _, _ = xargs.xargs(
+        exit_cmd, ('1',), negate=True, _max_length=max_length,
+    )
+    assert ret == 0
+
+    ret, _, _ = xargs.xargs(
+        exit_cmd, ('1', '0'), negate=True, _max_length=max_length,
+    )
+    assert ret == 1
+
+
+def test_xargs_retcode_normal():
+    ret, _, _ = xargs.xargs(exit_cmd, ('0',), _max_length=max_length)
+    assert ret == 0
+
+    ret, _, _ = xargs.xargs(exit_cmd, ('0', '1'), _max_length=max_length)
+    assert ret == 1