gitk: Fix the tab setting in the diff display window

This fixes the bug where we were using the wrong font to calculate
the width of the tab stops in the diff display window.

If we're running on Tk 8.5 we also use the new -tabstyle wordprocessor
option that makes tabs work as expected, i.e. a tab moves the cursor
to the right until the next tab stop is reached.  On Tk 8.5 we also
get fancy and set the first tab stop at column 1 for a normal diff
or column N for a merge diff with N parents.

On Tk8.4 we can't do that because the tabs work in the "tabular"
style, i.e. the nth tab character moves to the location of the nth
tab position, *unless* you ask for the default tab setting, which
gives 8-column tabs that work in the "wordprocessor" mode.  So on
Tk8.4 if the tab setting is 8 we ask for default tabs.  This means
that a tab setting of 7 or 9 can look quite different to 8 in some
cases.
Signed-off-by: NPaul Mackerras <paulus@samba.org>

gitk

@@ -626,6 +626,7 @@ proc makewindow {} {
     global bgcolor fgcolor bglist fglist diffcolors selectbgcolor
     global headctxmenu progresscanv progressitem progresscoords statusw
     global fprogitem fprogcoord lastprogupdate progupdatepending
+    global have_tk85
 
     menu .bar
     .bar add cascade -label "File" -menu .bar.file
@@ -845,9 +846,11 @@ proc makewindow {} {
     pack .bleft.mid.labeldiffcontext .bleft.mid.diffcontext -side left
     set ctext .bleft.ctext
     text $ctext -background $bgcolor -foreground $fgcolor \
-	-tabs "[expr {$tabstop * $charspc}]" \
 	-state disabled -font $textfont \
 	-yscrollcommand scrolltext -wrap none
+    if {$have_tk85} {
+	$ctext conf -tabstyle wordprocessor
+    }
     scrollbar .bleft.sb -command "$ctext yview"
     pack .bleft.top -side top -fill x
     pack .bleft.mid -side top -fill x
@@ -1135,7 +1138,7 @@ proc doprogupdate {} {
 }
 
 proc savestuff {w} {
-    global canv canv2 canv3 ctext cflist mainfont textfont uifont tabstop
+    global canv canv2 canv3 mainfont textfont uifont tabstop
     global stuffsaved findmergefiles maxgraphpct
     global maxwidth showneartags showlocalchanges
     global viewname viewfiles viewargs viewperm nextviewnum
@@ -5092,6 +5095,7 @@ proc showfile {f} {
     $ctext insert end "$f\n" filesep
     $ctext config -state disabled
     $ctext yview $commentend
+    settabs 0
 }
 
 proc getblobline {bf id} {
@@ -5133,6 +5137,7 @@ proc mergediff {id l} {
     fconfigure $mdf -blocking 0
     set mdifffd($id) $mdf
     set np [llength [lindex $parentlist $l]]
+    settabs $np
     filerun $mdf [list getmergediffline $mdf $id $np]
 }
 
@@ -5210,6 +5215,7 @@ proc getmergediffline {mdf id np} {
 proc startdiff {ids} {
     global treediffs diffids treepending diffmergeid nullid nullid2
 
+    settabs 1
     set diffids $ids
     catch {unset diffmergeid}
     if {![info exists treediffs($ids)] ||
@@ -5515,6 +5521,23 @@ proc clear_ctext {{first 1.0}} {
     }
 }
 
+proc settabs {{firstab {}}} {
+    global firsttabstop tabstop textfont ctext have_tk85
+
+    if {$firstab ne {} && $have_tk85} {
+	set firsttabstop $firstab
+    }
+    set w [font measure $textfont "0"]
+    if {$firsttabstop != 0} {
+	$ctext conf -tabs [list [expr {$firsttabstop * $w}] \
+			       [expr {($firsttabstop + $tabstop) * $w}]]
+    } elseif {$have_tk85 || $tabstop != 8} {
+	$ctext conf -tabs [expr {$tabstop * $w}]
+    } else {
+	$ctext conf -tabs {}
+    }
+}
+
 proc incrsearch {name ix op} {
     global ctext searchstring searchdirn
 
@@ -5666,13 +5689,12 @@ proc redisplay {} {
 
 proc incrfont {inc} {
     global mainfont textfont ctext canv phase cflist showrefstop
-    global charspc tabstop
     global stopped entries
     unmarkmatches
     set mainfont [lreplace $mainfont 1 1 [expr {[lindex $mainfont 1] + $inc}]]
     set textfont [lreplace $textfont 1 1 [expr {[lindex $textfont 1] + $inc}]]
     setcoords
-    $ctext conf -font $textfont -tabs "[expr {$tabstop * $charspc}]"
+    settabs
     $cflist conf -font $textfont
     $ctext tag conf filesep -font [concat $textfont bold]
     foreach e $entries {
@@ -5876,6 +5898,7 @@ proc lineclick {x y id isnew} {
     # fill the details pane with info about this line
     $ctext conf -state normal
     clear_ctext
+    settabs 0
     $ctext insert end "Parent:\t"
     $ctext insert end $id link0
     setlink $id link0
@@ -7780,6 +7803,7 @@ proc showtag {tag isnew} {
     }
     $ctext conf -state normal
     clear_ctext
+    settabs 0
     set linknum 0
     if {![info exists tagcontents($tag)]} {
 	catch {
@@ -7951,11 +7975,10 @@ proc prefscan {} {
 proc prefsok {} {
     global maxwidth maxgraphpct
     global oldprefs prefstop showneartags showlocalchanges
-    global charspc ctext tabstop
 
     catch {destroy $prefstop}
     unset prefstop
-    $ctext configure -tabs "[expr {$tabstop * $charspc}]"
+    settabs
     if {$showlocalchanges != $oldprefs(showlocalchanges)} {
 	if {$showlocalchanges} {
 	    doshowlocalchanges
@@ -8360,6 +8383,7 @@ if {$i >= [llength $argv] && $revtreeargs ne {}} {
 set nullid "0000000000000000000000000000000000000000"
 set nullid2 "0000000000000000000000000000000000000001"
 
+set have_tk85 [expr {[package vcompare $tk_version "8.5"] >= 0}]
 
 set runq {}
 set history {}
@@ -8376,6 +8400,7 @@ set markingmatches 0
 set linkentercount 0
 set need_redisplay 0
 set nrows_drawn 0
+set firsttabstop 0
 
 set nextviewnum 1
 set curview 0