checkpatch: add test for commit id formatting style in commit log

Commit logs have various forms of commit id references.

Try to standardize on a 12 character long lower case commit id along
with a description of parentheses and the quoted subject line.

ie: commit 0123456789ab ("commit description")

If git and a git tree exists, look up the commit id and emit the
appropriate line as part of the message.
Signed-off-by: Joe Perches <joe@perches.com>
Requested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -550,6 +550,34 @@ sub seed_camelcase_includes {
 	}
 }
 
+sub git_commit_info {
+	my ($commit, $id, $desc) = @_;
+
+	return ($id, $desc) if ((which("git") eq "") || !(-e ".git"));
+
+	my $output = `git log --no-color --format='%H %s' -1 $commit 2>&1`;
+	$output =~ s/^\s*//gm;
+	my @lines = split("\n", $output);
+
+	if ($lines[0] =~ /^error: short SHA1 $commit is ambiguous\./) {
+# Maybe one day convert this block of bash into something that returns
+# all matching commit ids, but it's very slow...
+#
+#		echo "checking commits $1..."
+#		git rev-list --remotes | grep -i "^$1" |
+#		while read line ; do
+#		    git log --format='%H %s' -1 $line |
+#		    echo "commit $(cut -c 1-12,41-)"
+#		done
+	} elsif ($lines[0] =~ /^fatal: ambiguous argument '$commit': unknown revision or path not in the working tree\./) {
+	} else {
+		$id = substr($lines[0], 0, 12);
+		$desc = substr($lines[0], 41);
+	}
+
+	return ($id, $desc);
+}
+
 $chk_signoff = 0 if ($file);
 
 my @rawlines = ();
@@ -674,6 +702,18 @@ sub format_email {
 	return $formatted_email;
 }
 
+sub which {
+    my ($bin) = @_;
+
+    foreach my $path (split(/:/, $ENV{PATH})) {
+	if (-e "$path/$bin") {
+	    return "$path/$bin";
+	}
+    }
+
+    return "";
+}
+
 sub which_conf {
 	my ($conf) = @_;
 
@@ -1958,6 +1998,20 @@ sub process {
 			      "Remove Gerrit Change-Id's before submitting upstream.\n" . $herecurr);
 		}
 
+# Check for improperly formed commit descriptions
+		if ($in_commit_log &&
+		    $line =~ /\bcommit\s+[0-9a-f]{5,}/i &&
+		    $line !~ /\b[Cc]ommit [0-9a-f]{12,16} \("/) {
+			$line =~ /\b(c)ommit\s+([0-9a-f]{5,})/i;
+			my $init_char = $1;
+			my $orig_commit = lc($2);
+			my $id = '01234567890ab';
+			my $desc = 'commit description';
+		        ($id, $desc) = git_commit_info($orig_commit, $id, $desc);
+			ERROR("GIT_COMMIT_ID",
+			      "Please use 12 to 16 chars for the git commit ID like: '${init_char}ommit $id (\"$desc\")'\n" . $herecurr);
+		}
+
 # Check for wrappage within a valid hunk of the file
 		if ($realcnt != 0 && $line !~ m{^(?:\+|-| |\\ No newline|$)}) {
 			ERROR("CORRUPTED_PATCH",