util: Add a git commit-msg hook

Add a git commit-msg hook that verifies that commit messages follow
gem5 guidelines.

Commit messages must contain the following components:
    <gem5_tags>: <title>

    <description>
    <patch_tags>

<gem5_tags> are comma separated keywords (found in MAINTAINERS) that
describe which sections of gem5 are being modified by the patch.
Two special keywords can also be used to imply that the author is
looking for feedback on the way their commit was implemented (RFC),
and to inform that the commit is a work in progress (WIP).

<title> A short and concise description of the commit without trailing
whitespaces

<description> is an optional (yet highly recommended) detailed
description of the objective of the commit.

<patch_tags> describe the metadata of the commit, and most of them
are automatically added by Gerrit.

Change-Id: Ib6fb6edf6d1417bfda23729b35c5b8ed44d2cf51
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21739
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

2 files changed, 136 insertions, 0 deletions

diff --git a/ext/git-commit-msg b/ext/git-commit-msg
index 60fe59da7..db83fd73c 100755
--- a/ext/git-commit-msg
+++ b/ext/git-commit-msg
@@ -189,3 +189,6 @@ _gen_ChangeId() {
 
 
 add_ChangeId
+
+# Perform gem5-specific commit message style check
+./util/git-commit-msg.py $MSG
diff --git a/util/git-commit-msg.py b/util/git-commit-msg.py
new file mode 100755
index 000000000..74c8f014a
--- /dev/null
+++ b/util/git-commit-msg.py
@@ -0,0 +1,133 @@
+#!/usr/bin/env python2.7
+#
+# Copyright (c) 2019 Inria
+# All rights reserved
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+# Authors: Daniel Carvalho
+
+# If your commit has been canceled because of this file, do not panic: a
+# copy of it has been stored in ./.git/COMMIT_EDITMSG
+
+import os
+import re
+import sys
+
+from style.repo import GitRepo
+
+def _printErrorQuit(error_message):
+    """
+        Print an error message, followed my a help message and inform failure.
+
+        @param error_message A message describing the error that caused the
+            failure.
+    """
+    print(error_message)
+    print("""
+The commit has been canceled, but a copy of it can be found in
+.git/COMMIT_EDITMSG
+
+The first line of a commit must contain one or more gem5 tags separated by
+commas (see MAINTAINERS for the possible tags), followed by a colon and a
+commit title. There must be no leading nor trailing whitespaces.
+
+This header line must then be followed by an empty line. A detailed message,
+although highly recommended, is not mandatory and can follow that empty line.
+
+e.g.:
+    cpu: Refactor branch predictors
+
+    Refactor branch predictor code to improve its readability, moving functions
+    X and Y to the base class...
+
+e.g.:
+    mem,mem-cache: Improve packet class readability
+
+    The packet class...
+""")
+    print("A copy of your commit message can be found in " + sys.argv[1])
+    sys.exit(1)
+
+def _validateTags(commit_header):
+    """
+        Check if all tags in the commit header belong to the list of valid
+        gem5 tags.
+
+        @param commit_header The first line of the commit message.
+    """
+
+    # List of valid tags
+    # @todo this is error prone, and should be extracted automatically from
+    #       a file
+    valid_tags = ["arch", "arch-alpha", "arch-arm", "arch-hsail", "arch-mips",
+        "arch-power", "arch-riscv", "arch-sparc", "arch-x86", "base",
+        "configs", "cpu", "cpu-kvm", "cpu-minor", "cpu-o3", "cpu-simple",
+        "dev", "dev-arm", "dev-virtio", "ext", "gpu-compute", "learning-gem5",
+        "mem", "mem-cache", "mem-garnet", "mem-ruby", "misc", "python",
+        "scons", "sim", "sim-se", "sim-power", "stats", "system",
+        "system-alpha", "system-arm", "systemc", "tests", "util", "RFC", "WIP"]
+
+    tags = ''.join(commit_header.split(':')[0].split()).split(',')
+    if (any(tag not in valid_tags for tag in tags)):
+        invalid_tag = next((tag for tag in tags if tag not in valid_tags))
+        _printErrorQuit("Invalid Gem5 tag: " + invalid_tag)
+
+# Go to git directory
+os.chdir(GitRepo().repo_base())
+
+# Get the commit message
+commit_message = open(sys.argv[1]).read()
+
+# The first line of a commit must contain at least one valid gem5 tag, and
+# a commit title
+commit_message_lines = commit_message.splitlines()
+commit_header = commit_message_lines[0]
+commit_header_match = \
+    re.search("^(\S[\w\-][,\s*[\w\-]+]*:.+\S$)", commit_header)
+if ((commit_header_match is None)):
+    _printErrorQuit("Invalid commit header")
+_validateTags(commit_header)
+
+# Make sure commit title does not exceed threshold. This line is limited to
+# a smaller number because version control systems may add a prefix, causing
+# line-wrapping for longer lines
+commit_title = commit_header.split(':')[1]
+max_header_size = 65
+if (len(commit_header) > max_header_size):
+    _printErrorQuit("The commit header (tags + title) is too long (" + \
+        str(len(commit_header)) + " > " + str(max_header_size) + ")")
+
+# Then there must be at least one empty line between the commit header and
+# the commit description
+if (commit_message_lines[1] != ""):
+    _printErrorQuit("Please add an empty line between the commit title and " \
+        "its description")
+
+# Encourage providing descriptions
+if (re.search("^(Signed-off-by|Change-Id|Reviewed-by):",
+    commit_message_lines[2])):
+    print("Warning: Commit does not have a description")
+
+sys.exit(0)