Experimental support for git commit-msg hook

Users can now install a git commit-msg hook using the --install-hook
commandline flag. This is still experimental and missing some important
features (uninstall, appending to existing hook, restoring incorrect
commit message).

README.md

@@ -66,6 +66,7 @@ Usage: gitlint [OPTIONS]
   Git lint tool, checks your git commit messages for styling issues
 
 Options:
+  --install-hook     [experimental] Install gitlint as a git commit-msg hook
   -C, --config PATH  Config file location (default: .gitlint).
   -c TEXT            Config flags in format <rule>.<option>=<value> (e.g.: -c
                      T1.line-length=80). Flag can be used multiple times to
@@ -138,6 +139,26 @@ B2    | body-trailing-whitespace    | Body cannot have trailing whitespace (spac
 B3    | body-hard-tab               | Body cannot contain hard tab characters (\t)
 B4    | body-first-line-empty       | First line of the body (second line of commit message) must be empty
 
+## Experimental: git commit-msg hook ##
+You can also install gitlint as a git ```commit-msg``` hook so that gitlint checks your commit messages automatically
+after each commit.
+
+```bash
+gitlint --install-hook
+```
+
+Note that this is still an experimental feature missing with some important gaps:
+- When your commit message fails to pass gitlint validation,  your commit is aborted (intended) and the commit message
+ you just entered will be lost (unintended). To make this a bit less inconvenient, the gitlint ```commit-msg``` hook
+ will print the commit message you just entered to the commandline so that you can copy-paste and reuse it (this only
+ happens if your commit message contained any violations).
+- You currently cannot uninstall the ```commit-msg``` hook using gitlint. You will need to manually remove the hook from
+  ```.git/hooks/commit-msg``` in your local git repository.
+- Gitlint cannot work together with an existing hook. If you already have a ```.git/hooks/commit-msg``` file in your
+  local repository, gitlint will refuse to install the ```commit-msg``` hook.
+
+
+
 ## Development ##
 
 To run tests:

gitlint/cli.py

@@ -1,6 +1,7 @@
 import gitlint
 from gitlint.lint import GitLinter
 from gitlint.config import LintConfig, LintConfigError
+from gitlint.hooks import GitHookInstaller
 import os
 import click
 import sys
@@ -35,6 +36,7 @@ def get_lint_config(config_path=None):
 
 
 @click.command()
+@click.option('--install-hook', is_flag=True, help="[experimental] Install gitlint as a git commit-msg hook")
 @click.option('-C', '--config', type=click.Path(exists=True),
               help="Config file location (default: {0}).".format(DEFAULT_CONFIG_FILE))
 @click.option('-c', multiple=True,
@@ -45,9 +47,12 @@ def get_lint_config(config_path=None):
               help="Verbosity, more v's for more verbose output (e.g.: -v, -vv, -vvv). Default: -vvv", )
 @click.option('-s', '--silent', help="Silent mode (no output). Takes precedence over -v, -vv, -vvv.", is_flag=True)
 @click.version_option(version=gitlint.__version__)
-def cli(config, c, ignore, verbose, silent):
+def cli(install_hook, config, c, ignore, verbose, silent):
     """ Git lint tool, checks your git commit messages for styling issues """
 
+    if install_hook:
+        GitHookInstaller.install_commit_msg_hook()
+
     try:
         # Config precedence:
         # First, load default config or config from configfile

gitlint/hooks.py

@@ -0,0 +1,31 @@
+import shutil
+import stat
+import sys
+import os
+
+COMMIT_MSG_HOOK_SRC_PATH = os.path.join(os.path.dirname(os.path.abspath(__file__)), "hooks/commit-msg")
+COMMIT_MSG_HOOK_DST_PATH = os.path.abspath(".git/hooks/commit-msg")
+
+
+class GitHookInstaller(object):
+    @staticmethod
+    def install_commit_msg_hook():
+        # assert that current directory is a git repository
+        if not os.path.isdir(".git/hooks"):
+            sys.stderr.write("The current directory is not a git repository\n")
+            exit(1)
+        if os.path.exists(COMMIT_MSG_HOOK_DST_PATH):
+            sys.stderr.write(
+                "There is already a commit-msg hook file present in {}. \n".format(COMMIT_MSG_HOOK_DST_PATH) +
+                "gitlint currently does not support appending to an existing commit-msg file.\n")
+            exit(1)
+
+        # copy hook file
+        shutil.copy(COMMIT_MSG_HOOK_SRC_PATH, COMMIT_MSG_HOOK_DST_PATH)
+        # make hook executable
+        st = os.stat(COMMIT_MSG_HOOK_DST_PATH)
+        os.chmod(COMMIT_MSG_HOOK_DST_PATH, st.st_mode | stat.S_IEXEC)
+
+        # declare victory :-)
+        sys.stdout.write("Successfully installed gitlint commit-msg hook in {0}\n".format(COMMIT_MSG_HOOK_DST_PATH))
+        exit(0)

gitlint/hooks/commit-msg

@@ -0,0 +1,18 @@
+#!/bin/sh
+### gitlint commit-msg hook start ###
+
+cat "$1" | gitlint
+gitlint_exit_code=$?
+
+if [ $gitlint_exit_code -gt 0 ]; then
+    echo "----------------------"
+    echo "Your commit message: "
+    echo "----------------------"
+    cat "$1" | grep -v '^#'
+else
+    echo "gitlint: OK"
+fi
+
+exit $gitlint_exit_code
+
+### gitlint commit-msg hook end ###

setup.py

@@ -26,7 +26,7 @@ def get_version(package):
     description="Linter for git repositories. Under active development.",
     long_description=long_description,
     classifiers=[
-        "Development Status :: 3 - Alpha",
+        "Development Status :: 4 - Beta",
         "Operating System :: OS Independent",
         "Programming Language :: Python",
         "Environment :: Console",
@@ -41,6 +41,9 @@ def get_version(package):
     author='Joris Roovers',
     url='https://github.com/jorisroovers/gitlint',
     license='MIT',
+    package_data={
+        'gitlint': ['hooks/*']
+    },
     packages=find_packages(exclude=["examples"]),
     entry_points={
         "console_scripts": [