gitk: Fix some corner cases in computing vrowmod and displayorder

First, insertfakerow and removefakerow weren't updating vrowmod,
and hence displayorder was not getting updated when it needed to,
in the case where the fake row was being inserted into or removed
from the last arc.  The comparison of varctok vs vtokmod was moved
into modify_arc for these cases (and for the call in rewrite_commit)
to avoid duplicating the extra code needed.  Second, the logic in
update_arcrows didn't end up truncating displayorder and unsetting
cached_commitrow if the first modified row was in the last arc.
This fixes these problems.
Signed-off-by: NPaul Mackerras <paulus@samba.org>

gitk

@@ -609,9 +609,7 @@ proc insertfakerow {id p} {
     set numcommits [incr commitidx($v)]
     # note we deliberately don't update varcstart($v) even if $i == 0
     set varccommits($v,$a) [linsert $varccommits($v,$a) $i $id]
-    if {[string compare [lindex $varctok($v) $a] $vtokmod($v)] < 0} {
-	modify_arc $v $a $i
-    }
+    modify_arc $v $a $i
     if {[info exists targetid]} {
 	if {![comes_before $targetid $p]} {
 	    incr targetrow
@@ -648,9 +646,7 @@ proc removefakerow {id} {
     if {$j >= 0} {
 	set children($v,$p) [lreplace $children($v,$p) $j $j]
     }
-    if {[string compare [lindex $varctok($v) $a] $vtokmod($v)] < 0} {
-	modify_arc $v $a $i
-    }
+    modify_arc $v $a $i
     if {[info exist currentid] && $id eq $currentid} {
 	unset currentid
 	unset selectedline
@@ -693,9 +689,19 @@ proc vtokcmp {v a b} {
 		[lindex $varctok($v) $varcid($v,$b)]]
 }
 
+# This assumes that if lim is not given, the caller has checked that
+# arc a's token is less than $vtokmod($v)
 proc modify_arc {v a {lim {}}} {
     global varctok vtokmod varcmod varcrow vupptr curview vrowmod varccommits
 
+    if {$lim ne {}} {
+	set c [string compare [lindex $varctok($v) $a] $vtokmod($v)]
+	if {$c > 0} return
+	if {$c == 0} {
+	    set r [lindex $varcrow($v) $a]
+	    if {$r ne {} && $vrowmod($v) <= $r + $lim} return
+	}
+    }
     set vtokmod($v) [lindex $varctok($v) $a]
     set varcmod($v) $a
     if {$v == $curview} {
@@ -721,6 +727,14 @@ proc update_arcrows {v} {
     global vupptr vdownptr vleftptr varctok
     global displayorder parentlist curview cached_commitrow
 
+    if {$vrowmod($v) == $commitidx($v)} return
+    if {$v == $curview} {
+	if {[llength $displayorder] > $vrowmod($v)} {
+	    set displayorder [lrange $displayorder 0 [expr {$vrowmod($v) - 1}]]
+	    set parentlist [lrange $parentlist 0 [expr {$vrowmod($v) - 1}]]
+	}
+	catch {unset cached_commitrow}
+    }
     set narctot [expr {[llength $varctok($v)] - 1}]
     set a $varcmod($v)
     while {$a != 0 && [lindex $varcix($v) $a] eq {}} {
@@ -739,23 +753,12 @@ proc update_arcrows {v} {
 	set row 0
     } else {
 	set arcn [lindex $varcix($v) $a]
-	# see if a is the last arc; if so, nothing to do
-	if {$arcn == $narctot - 1} {
-	    return
-	}
 	if {[llength $vrownum($v)] > $arcn + 1} {
 	    set vrownum($v) [lrange $vrownum($v) 0 $arcn]
 	    set varcorder($v) [lrange $varcorder($v) 0 $arcn]
 	}
 	set row [lindex $varcrow($v) $a]
     }
-    if {$v == $curview} {
-	if {[llength $displayorder] > $vrowmod($v)} {
-	    set displayorder [lrange $displayorder 0 [expr {$vrowmod($v) - 1}]]
-	    set parentlist [lrange $parentlist 0 [expr {$vrowmod($v) - 1}]]
-	}
-	catch {unset cached_commitrow}
-    }
     while {1} {
 	set p $a
 	incr row [llength $varccommits($v,$a)]
@@ -969,11 +972,9 @@ proc rewrite_commit {v id rwid} {
 	# fix the graph after joining $id to $rwid
 	set a $varcid($v,$ch)
 	fix_reversal $rwid $a $v
-	if {[string compare [lindex $varctok($v) $a] $vtokmod($v)] < 0} {
-	    # parentlist is wrong for the last element of arc $a
-	    # even if displayorder is right, hence the 3rd arg here
-	    modify_arc $v $a [expr {[llength $varccommits($v,$a)] - 1}]
-	}
+	# parentlist is wrong for the last element of arc $a
+	# even if displayorder is right, hence the 3rd arg here
+	modify_arc $v $a [expr {[llength $varccommits($v,$a)] - 1}]
     }
 }