git-gui: remove lines starting with the comment character

The comment character is specified by the config variable
'core.commentchar'. Any lines starting with this character is considered
a comment and should not be included in the final commit message.

Teach git-gui to filter out lines in the commit message that start with
the comment character using git-stripspace. If the config is not set,
'#' is taken as the default. Also add a message educating users about
the comment character.

Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

git-gui.sh

@@ -875,6 +875,7 @@ set default_config(merge.summary) false
 set default_config(merge.verbosity) 2
 set default_config(user.name) {}
 set default_config(user.email) {}
+set default_config(core.commentchar) "#"
 
 set default_config(gui.encoding) [encoding system]
 set default_config(gui.matchtrackingbranch) false
@@ -3436,6 +3437,10 @@ proc trace_commit_type {varname args} {
 	merge         {set txt [mc "Merge Commit Message:"]}
 	*             {set txt [mc "Commit Message:"]}
 	}
+
+	set comment_char [get_config core.commentchar]
+	set txt [string cat $txt \
+				 [mc " (Lines starting with '$comment_char' will be ignored)"]]
 	$ui_coml conf -text $txt
 }
 trace add variable commit_type write trace_commit_type

lib/commit.tcl

@@ -141,6 +141,20 @@ proc setup_commit_encoding {msg_wt {quiet 0}} {
 	}
 }
 
+proc strip_msg {msg} {
+	set cmd [concat [list | ] [_git_cmd stripspace] --strip-comments]
+	_trace_exec $cmd
+	set fd [open $cmd r+]
+	fconfigure $fd -translation binary -encoding utf-8
+
+	puts -nonewline $fd $msg
+	close $fd w
+	set result [read $fd]
+	close $fd
+
+	return $result
+}
+
 proc commit_tree {} {
 	global HEAD commit_type file_states ui_comm repo_config
 	global pch_error
@@ -207,8 +221,8 @@ You must stage at least 1 file before you can commit.
 
 	# -- A message is required.
 	#
-	set msg [string trim [$ui_comm get 1.0 end]]
-	regsub -all -line {[ \t\r]+$} $msg {} msg
+	set msg [strip_msg [$ui_comm get 1.0 end]]
+
 	if {$msg eq {}} {
 		error_popup [mc "Please supply a commit message.