git-gui: improve dark mode support

The colors of some ttext widgets are hard-coded. These hard-coded colors
are okay with a light theme but with a dark theme some widgets are dark
colored and the hard-coded ones are still light. This defeats the
purpose of applying the theme and makes the UI look very awkward.

Remove the hard-coded colors in ttext calls and use colors from the
theme for those widgets via Text.Background and Text.Foreground from the
option database.

Similarly, the highlighting for the currently selected file(s) in the
"Staged Files" and "Unstaged Files" sections is also hard-coded. Pull
the colors for that from the current theme to make sure it is in line

Signed-off-by: Serg Tereshchenko <serg.partizan@gmail.com>
Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

git-gui.sh

@@ -720,7 +720,9 @@ proc rmsel_tag {text} {
 		-background [$text cget -background] \
 		-foreground [$text cget -foreground] \
 		-borderwidth 0
-	$text tag conf in_sel -background lightgray
+	$text tag conf in_sel\
+		-background $color::select_bg \
+		-foreground $color::select_fg
 	bind $text <Motion> break
 	return $text
 }
@@ -863,6 +865,7 @@ proc apply_config {} {
 			set NS ttk
 			bind [winfo class .] <<ThemeChanged>> [list InitTheme]
 			pave_toplevel .
+			color::sync_with_theme
 		}
 	}
 }
@@ -3272,7 +3275,7 @@ pack .vpane -anchor n -side top -fill both -expand 1
 textframe .vpane.files.workdir -height 100 -width 200
 tlabel .vpane.files.workdir.title -text [mc "Unstaged Changes"] \
 	-background lightsalmon -foreground black
-ttext $ui_workdir -background white -foreground black \
+ttext $ui_workdir \
 	-borderwidth 0 \
 	-width 20 -height 10 \
 	-wrap none \
@@ -3294,7 +3297,7 @@ textframe .vpane.files.index -height 100 -width 200
 tlabel .vpane.files.index.title \
 	-text [mc "Staged Changes (Will Commit)"] \
 	-background lightgreen -foreground black
-ttext $ui_index -background white -foreground black \
+ttext $ui_index \
 	-borderwidth 0 \
 	-width 20 -height 10 \
 	-wrap none \
@@ -3321,7 +3324,9 @@ if {!$use_ttk} {
 
 foreach i [list $ui_index $ui_workdir] {
 	rmsel_tag $i
-	$i tag conf in_diff -background [$i tag cget in_sel -background]
+	$i tag conf in_diff \
+		-background $color::select_bg \
+		-foreground $color::select_fg
 }
 unset i
 
@@ -3429,7 +3434,7 @@ if {![is_enabled nocommit]} {
 }
 
 textframe .vpane.lower.commarea.buffer.frame
-ttext $ui_comm -background white -foreground black \
+ttext $ui_comm \
 	-borderwidth 1 \
 	-undo true \
 	-maxundo 20 \
@@ -3558,7 +3563,7 @@ bind .vpane.lower.diff.header.path <Button-1> {do_file_open $current_diff_path}
 #
 textframe .vpane.lower.diff.body
 set ui_diff .vpane.lower.diff.body.t
-ttext $ui_diff -background white -foreground black \
+ttext $ui_diff \
 	-borderwidth 0 \
 	-width 80 -height 5 -wrap none \
 	-font font_diff \

lib/themed.tcl

@@ -1,6 +1,44 @@
 # Functions for supporting the use of themed Tk widgets in git-gui.
 # Copyright (C) 2009 Pat Thoyts <patthoyts@users.sourceforge.net>
 
+
+namespace eval color {
+	# Variable colors
+	# Preffered way to set widget colors is using add_option.
+	# In some cases, like with tags in_diff/in_sel, we use these colors.
+	variable select_bg		lightgray
+	variable select_fg		black
+
+	proc sync_with_theme {} {
+		set base_bg		[ttk::style lookup . -background]
+		set base_fg		[ttk::style lookup . -foreground]
+		set text_bg		[ttk::style lookup Treeview -background]
+		set text_fg		[ttk::style lookup Treeview -foreground]
+		set select_bg	[ttk::style lookup Default -selectbackground]
+		set select_fg	[ttk::style lookup Default -selectforeground]
+
+		set color::select_bg $select_bg
+		set color::select_fg $select_fg
+
+		proc add_option {key val} {
+			option add $key $val widgetDefault
+		}
+		# Add options for plain Tk widgets
+		# Using `option add` instead of tk_setPalette to avoid unintended
+		# consequences.
+		if {![is_MacOSX]} {
+			add_option *Menu.Background $base_bg
+			add_option *Menu.Foreground $base_fg
+			add_option *Menu.activeBackground $select_bg
+			add_option *Menu.activeForeground $select_fg
+		}
+		add_option *Text.Background $text_bg
+		add_option *Text.Foreground $text_fg
+		add_option *Text.HighlightBackground $base_bg
+		add_option *Text.HighlightColor $select_bg
+	}
+}
+
 proc ttk_get_current_theme {} {
 	# Handle either current Tk or older versions of 8.5
 	if {[catch {set theme [ttk::style theme use]}]} {