git-gui: Implement system-wide configuration handling.

With the old implementation any system-wide options appear
to be set locally in the current repository. This commit
adds explicit handling of system options, essentially
interpreting them as customized default_config.

The difficulty in interpreting system options stems from
the fact that simple 'git config' lists all values, while
'git config --global' only values set in ~/.gitconfig,
excluding both local and system options.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -940,19 +940,25 @@ git-version proc _parse_config {arr_name args} {
 }
 
 proc load_config {include_global} {
-	global repo_config global_config default_config
+	global repo_config global_config system_config default_config
 
 	if {$include_global} {
+		_parse_config system_config --system
 		_parse_config global_config --global
 	}
 	_parse_config repo_config
 
 	foreach name [array names default_config] {
+		if {[catch {set v $system_config($name)}]} {
+			set system_config($name) $default_config($name)
+		}
+	}
+	foreach name [array names system_config] {
 		if {[catch {set v $global_config($name)}]} {
-			set global_config($name) $default_config($name)
+			set global_config($name) $system_config($name)
 		}
 		if {[catch {set v $repo_config($name)}]} {
-			set repo_config($name) $default_config($name)
+			set repo_config($name) $system_config($name)
 		}
 	}
 }

lib/option.tcl

@@ -25,7 +25,7 @@ proc config_check_encodings {} {
 
 proc save_config {} {
 	global default_config font_descs
-	global repo_config global_config
+	global repo_config global_config system_config
 	global repo_config_new global_config_new
 	global ui_comm_spell
 
@@ -49,7 +49,7 @@ proc save_config {} {
 	foreach name [array names default_config] {
 		set value $global_config_new($name)
 		if {$value ne $global_config($name)} {
-			if {$value eq $default_config($name)} {
+			if {$value eq $system_config($name)} {
 				catch {git config --global --unset $name}
 			} else {
 				regsub -all "\[{}\]" $value {"} value
@@ -284,17 +284,17 @@ proc do_options {} {
 }
 
 proc do_restore_defaults {} {
-	global font_descs default_config repo_config
+	global font_descs default_config repo_config system_config
 	global repo_config_new global_config_new
 
 	foreach name [array names default_config] {
-		set repo_config_new($name) $default_config($name)
-		set global_config_new($name) $default_config($name)
+		set repo_config_new($name) $system_config($name)
+		set global_config_new($name) $system_config($name)
 	}
 
 	foreach option $font_descs {
 		set name [lindex $option 0]
-		set repo_config(gui.$name) $default_config(gui.$name)
+		set repo_config(gui.$name) $system_config(gui.$name)
 	}
 	apply_config