git-gui: use commit message template

Use the file described by commit.template (if set) to show the commit message
template, just like other GUIs.

Signed-off-by: Martin Schön <Martin.Schoen@loewensteinmedical.de>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

Author: LoewensteinMedicalTechnology

git-gui.sh

@@ -1482,6 +1482,7 @@ proc rescan {after {honor_trustmtime 1}} {
 		} elseif {[run_prepare_commit_msg_hook]} {
 		} elseif {[load_message MERGE_MSG]} {
 		} elseif {[load_message SQUASH_MSG]} {
+		} elseif {[load_message [get_config commit.template]]} {
 		}
 		$ui_comm edit reset
 		$ui_comm edit modified false
@@ -1616,6 +1617,12 @@ proc run_prepare_commit_msg_hook {} {
 		fconfigure $fd_sm -encoding utf-8
 		puts -nonewline $fd_pcm [read $fd_sm]
 		close $fd_sm
+	} elseif {[file isfile [get_config commit.template]]} {
+		set pcm_source "template"
+		set fd_sm [open [get_config commit.template] r]
+		fconfigure $fd_sm -encoding utf-8
+		puts -nonewline $fd_pcm [read $fd_sm]
+		close $fd_sm
 	} else {
 		set pcm_source ""
 	}

lib/commit.tcl

@@ -456,6 +456,7 @@ A rescan will be automatically started now.
 	}
 
 	$ui_comm delete 0.0 end
+	load_message [get_config commit.template]
 	$ui_comm edit reset
 	$ui_comm edit modified false
 	if {$::GITGUI_BCK_exists} {