git-gui: Disable diff actions when no diff is active.

There is no reason why the user should be able to operate on the diff
buffer if there is no currently selected diff; likewise the "File:"
label text appears rather silly looking all by itself when no diff
is being shown in the diff buffer.

So now we only enable widgets (like menu items) if there is a diff
currently showing, and we disable them when a diff isn't showing.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui

@@ -455,34 +455,33 @@ proc prune_selection {} {
 ## diff
 
 proc clear_diff {} {
-	global ui_diff ui_fname_value ui_fstatus_value ui_index ui_other
+	global ui_diff current_diff ui_index ui_other
 
 	$ui_diff conf -state normal
 	$ui_diff delete 0.0 end
 	$ui_diff conf -state disabled
 
-	set ui_fname_value {}
-	set ui_fstatus_value {}
+	set current_diff {}
 
 	$ui_index tag remove in_diff 0.0 end
 	$ui_other tag remove in_diff 0.0 end
 }
 
 proc reshow_diff {} {
-	global ui_fname_value ui_status_value file_states
+	global current_diff ui_status_value file_states
 
-	if {$ui_fname_value eq {}
-		|| [catch {set s $file_states($ui_fname_value)}]} {
+	if {$current_diff eq {}
+		|| [catch {set s $file_states($current_diff)}]} {
 		clear_diff
 	} else {
-		show_diff $ui_fname_value
+		show_diff $current_diff
 	}
 }
 
 proc handle_empty_diff {} {
-	global ui_fname_value file_states file_lists
+	global current_diff file_states file_lists
 
-	set path $ui_fname_value
+	set path $current_diff
 	set s $file_states($path)
 	if {[lindex $s 0] ne {_M}} return
 
@@ -520,7 +519,7 @@ files list, to prevent possible confusion.
 proc show_diff {path {w {}} {lno {}}} {
 	global file_states file_lists
 	global PARENT diff_3way diff_active repo_config
-	global ui_diff ui_fname_value ui_fstatus_value ui_status_value
+	global ui_diff current_diff ui_status_value
 
 	if {$diff_active || ![lock_index read]} return
 
@@ -542,8 +541,7 @@ proc show_diff {path {w {}} {lno {}}} {
 	set m [lindex $s 0]
 	set diff_3way 0
 	set diff_active 1
-	set ui_fname_value $path
-	set ui_fstatus_value [mapdesc $m $path]
+	set current_diff $path
 	set ui_status_value "Loading diff of [escape_path $path]..."
 
 	set cmd [list | git diff-index]
@@ -1261,7 +1259,7 @@ proc update_index {msg pathList after} {
 
 proc write_update_index {fd pathList totalCnt batch msg after} {
 	global update_index_cp update_index_rsd ui_status_value
-	global file_states ui_fname_value
+	global file_states current_diff
 
 	if {$update_index_cp >= $totalCnt} {
 		close $fd
@@ -1296,7 +1294,7 @@ proc write_update_index {fd pathList totalCnt batch msg after} {
 		puts -nonewline $fd $path
 		puts -nonewline $fd "\0"
 		display_file $path $new
-		if {$ui_fname_value eq $path} {
+		if {$current_diff eq $path} {
 			set update_index_rsd 1
 		}
 	}
@@ -2384,71 +2382,105 @@ pack .vpane.lower.commarea.buffer -side left -fill y
 
 # -- Commit Message Buffer Context Menu
 #
-menu $ui_comm.ctxm -tearoff 0
-$ui_comm.ctxm add command -label "Cut" \
+set ctxm .vpane.lower.commarea.buffer.ctxm
+menu $ctxm -tearoff 0
+$ctxm add command \
+	-label {Cut} \
 	-font font_ui \
-	-command "tk_textCut $ui_comm"
-$ui_comm.ctxm add command -label "Copy" \
+	-command {tk_textCut $ui_comm}
+$ctxm add command \
+	-label {Copy} \
 	-font font_ui \
-	-command "tk_textCopy $ui_comm"
-$ui_comm.ctxm add command -label "Paste" \
+	-command {tk_textCopy $ui_comm}
+$ctxm add command \
+	-label {Paste} \
 	-font font_ui \
-	-command "tk_textPaste $ui_comm"
-$ui_comm.ctxm add command -label "Delete" \
+	-command {tk_textPaste $ui_comm}
+$ctxm add command \
+	-label {Delete} \
 	-font font_ui \
-	-command "$ui_comm delete sel.first sel.last"
-$ui_comm.ctxm add separator
-$ui_comm.ctxm add command -label "Select All" \
+	-command {$ui_comm delete sel.first sel.last}
+$ctxm add separator
+$ctxm add command \
+	-label {Select All} \
 	-font font_ui \
-	-command "$ui_comm tag add sel 0.0 end"
-$ui_comm.ctxm add command -label "Copy All" \
+	-command {$ui_comm tag add sel 0.0 end}
+$ctxm add command \
+	-label {Copy All} \
 	-font font_ui \
-	-command "
+	-command {
 		$ui_comm tag add sel 0.0 end
 		tk_textCopy $ui_comm
 		$ui_comm tag remove sel 0.0 end
-	"
-$ui_comm.ctxm add separator
-$ui_comm.ctxm add command -label "Sign Off" \
+	}
+$ctxm add separator
+$ctxm add command \
+	-label {Sign Off} \
 	-font font_ui \
 	-command do_signoff
-bind_button3 $ui_comm "tk_popup $ui_comm.ctxm %X %Y"
+bind_button3 $ui_comm "tk_popup $ctxm %X %Y"
 
 # -- Diff Header
-set ui_fname_value {}
-set ui_fstatus_value {}
+set current_diff {}
+set diff_actions [list]
+proc current_diff_trace {varname args} {
+	global current_diff diff_actions file_states
+	if {$current_diff eq {}} {
+		set s {}
+		set f {}
+		set p {}
+		set o disabled
+	} else {
+		set p $current_diff
+		set s [mapdesc [lindex $file_states($p) 0] $p]
+		set f {File:}
+		set p [escape_path $p]
+		set o normal
+	}
+
+	.vpane.lower.diff.header.status configure -text $s
+	.vpane.lower.diff.header.file configure -text $f
+	.vpane.lower.diff.header.path configure -text $p
+	foreach w $diff_actions {
+		uplevel #0 $w $o
+	}
+}
+trace add variable current_diff write current_diff_trace
+
 frame .vpane.lower.diff.header -background orange
-label .vpane.lower.diff.header.l4 \
-	-textvariable ui_fstatus_value \
+label .vpane.lower.diff.header.status \
 	-background orange \
 	-width $max_status_desc \
 	-anchor w \
 	-justify left \
 	-font font_ui
-label .vpane.lower.diff.header.l1 -text {File:} \
+label .vpane.lower.diff.header.file \
 	-background orange \
+	-anchor w \
+	-justify left \
 	-font font_ui
-set ui_fname .vpane.lower.diff.header.l2
-label $ui_fname \
-	-textvariable ui_fname_value \
+label .vpane.lower.diff.header.path \
 	-background orange \
 	-anchor w \
 	-justify left \
 	-font font_ui
-menu $ui_fname.ctxm -tearoff 0
-$ui_fname.ctxm add command -label "Copy" \
+pack .vpane.lower.diff.header.status -side left
+pack .vpane.lower.diff.header.file -side left
+pack .vpane.lower.diff.header.path -fill x
+set ctxm .vpane.lower.diff.header.ctxm
+menu $ctxm -tearoff 0
+$ctxm add command \
+	-label {Copy} \
 	-font font_ui \
 	-command {
 		clipboard clear
 		clipboard append \
 			-format STRING \
 			-type STRING \
-			-- $ui_fname_value
+			-- $current_diff
 	}
-bind_button3 $ui_fname "tk_popup $ui_fname.ctxm %X %Y"
-pack .vpane.lower.diff.header.l4 -side left
-pack .vpane.lower.diff.header.l1 -side left
-pack $ui_fname -fill x
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+bind_button3 .vpane.lower.diff.header.path "tk_popup $ctxm %X %Y"
 
 # -- Diff Body
 frame .vpane.lower.diff.body
@@ -2478,48 +2510,63 @@ $ui_diff tag conf bold -font font_diffbold
 
 # -- Diff Body Context Menu
 #
-menu $ui_diff.ctxm -tearoff 0
-$ui_diff.ctxm add command -label "Copy" \
+set ctxm .vpane.lower.diff.body.ctxm
+menu $ctxm -tearoff 0
+$ctxm add command \
+	-label {Copy} \
 	-font font_ui \
-	-command "tk_textCopy $ui_diff"
-$ui_diff.ctxm add command -label "Select All" \
+	-command {tk_textCopy $ui_diff}
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add command \
+	-label {Select All} \
 	-font font_ui \
-	-command "$ui_diff tag add sel 0.0 end"
-$ui_diff.ctxm add command -label "Copy All" \
+	-command {$ui_diff tag add sel 0.0 end}
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add command \
+	-label {Copy All} \
 	-font font_ui \
-	-command "
+	-command {
 		$ui_diff tag add sel 0.0 end
 		tk_textCopy $ui_diff
 		$ui_diff tag remove sel 0.0 end
-	"
-$ui_diff.ctxm add separator
-$ui_diff.ctxm add command -label "Decrease Font Size" \
+	}
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add separator
+$ctxm add command \
+	-label {Decrease Font Size} \
 	-font font_ui \
 	-command {incr_font_size font_diff -1}
-$ui_diff.ctxm add command -label "Increase Font Size" \
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add command \
+	-label {Increase Font Size} \
 	-font font_ui \
 	-command {incr_font_size font_diff 1}
-$ui_diff.ctxm add separator
-$ui_diff.ctxm add command -label "Show Less Context" \
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add separator
+$ctxm add command \
+	-label {Show Less Context} \
 	-font font_ui \
-	-command {if {$ui_fname_value ne {}
-		&& $repo_config(gui.diffcontext) >= 2} {
+	-command {if {$repo_config(gui.diffcontext) >= 2} {
 		incr repo_config(gui.diffcontext) -1
 		reshow_diff
 	}}
-$ui_diff.ctxm add command -label "Show More Context" \
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add command \
+	-label {Show More Context} \
 	-font font_ui \
-	-command {if {$ui_fname_value ne {}} {
+	-command {
 		incr repo_config(gui.diffcontext)
 		reshow_diff
-	}}
-$ui_diff.ctxm add separator
-$ui_diff.ctxm add command -label {Options...} \
+	}
+lappend diff_actions [list $ctxm entryconf [$ctxm index last] -state]
+$ctxm add separator
+$ctxm add command -label {Options...} \
 	-font font_ui \
 	-command do_options
-bind_button3 $ui_diff "tk_popup $ui_diff.ctxm %X %Y"
+bind_button3 $ui_diff "tk_popup $ctxm %X %Y"
 
 # -- Status Bar
+#
 set ui_status_value {Initializing...}
 label .status -textvariable ui_status_value \
 	-anchor w \
@@ -2530,6 +2577,7 @@ label .status -textvariable ui_status_value \
 pack .status -anchor w -side bottom -fill x
 
 # -- Load geometry
+#
 catch {
 set gm $repo_config(gui.geometry)
 wm geometry . [lindex $gm 0]
@@ -2543,6 +2591,7 @@ unset gm
 }
 
 # -- Key Bindings
+#
 bind $ui_comm <$M1B-Key-Return> {do_commit;break}
 bind $ui_comm <$M1B-Key-i> {do_include_all;break}
 bind $ui_comm <$M1B-Key-I> {do_include_all;break}
@@ -2590,6 +2639,7 @@ unset i
 
 set file_lists($ui_index) [list]
 set file_lists($ui_other) [list]
+set current_diff {}
 
 wm title . "$appname ([file normalize [file dirname $gitdir]])"
 focus -force $ui_comm