Improve the merge display when the result differs from all parents.

Now we see if the result is quite similar to one of the parents, and
if it is, display the result as a diff from that parent.  If the result
is similar to more than one parent, pick the one that it's most
similar to.

gitk

@@ -2054,7 +2054,6 @@ proc processgroup {} {
     set pnum 0
     foreach p $parents($id) {
 	set startline [expr {$grouplinestart + $diffoffset($p)}]
-	set offset($p) $diffoffset($p)
 	set ol $startline
 	set nl $grouplinestart
 	if {[info exists grouphunks($p)]} {
@@ -2098,9 +2097,8 @@ proc processgroup {} {
     set events [lsort -integer -index 0 $events]
     set nevents [llength $events]
     set nmerge $nparents($diffmergeid)
-    set i 0
     set l $grouplinestart
-    while {$i < $nevents} {
+    for {set i 0} {$i < $nevents} {set i $j} {
 	set nl [lindex $events $i 0]
 	while {$l < $nl} {
 	    $ctext insert end " $filelines($id,$f,$l)\n"
@@ -2129,7 +2127,9 @@ proc processgroup {} {
 	}
 	set nlc [expr {$enl - $l}]
 	set ncol mresult
+	set bestpn -1
 	if {[llength $active] == $nmerge - 1} {
+	    # no diff for one of the parents, i.e. it's identical
 	    for {set pnum 0} {$pnum < $nmerge} {incr pnum} {
 		if {![info exists delta($pnum)]} {
 		    if {$pnum < $mergemax} {
@@ -2140,11 +2140,25 @@ proc processgroup {} {
 		    break
 		}
 	    }
+	} elseif {[llength $active] == $nmerge} {
+	    # all parents are different, see if one is very similar
+	    set bestsim 30
+	    for {set pnum 0} {$pnum < $nmerge} {incr pnum} {
+		set sim [similarity $pnum $l $nlc $f \
+			     [lrange $events $i [expr {$j-1}]]]
+		if {$sim > $bestsim} {
+		    set bestsim $sim
+		    set bestpn $pnum
+		}
+	    }
+	    if {$bestpn >= 0} {
+		lappend ncol m$bestpn
+	    }
 	}
 	set pnum -1
 	foreach p $parents($id) {
 	    incr pnum
-	    if {![info exists delta($pnum)]} continue
+	    if {![info exists delta($pnum)] || $pnum == $bestpn} continue
 	    set olc [expr {$nlc + $delta($pnum)}]
 	    set ol [expr {$l + $diffoffset($p)}]
 	    incr diffoffset($p) $delta($pnum)
@@ -2154,11 +2168,35 @@ proc processgroup {} {
 		incr ol
 	    }
 	}
-	for {} {$nlc > 0} {incr nlc -1} {
+	set endl [expr {$l + $nlc}]
+	if {$bestpn >= 0} {
+	    # show this pretty much as a normal diff
+	    set p [lindex $parents($id) $bestpn]
+	    set ol [expr {$l + $diffoffset($p)}]
+	    incr diffoffset($p) $delta($bestpn)
+	    unset delta($bestpn)
+	    for {set k $i} {$k < $j} {incr k} {
+		set e [lindex $events $k]
+		if {[lindex $e 2] != $bestpn} continue
+		set nl [lindex $e 0]
+		set ol [expr {$ol + $nl - $l}]
+		for {} {$l < $nl} {incr l} {
+		    $ctext insert end "+$filelines($id,$f,$l)\n" $ncol
+		}
+		set c [lindex $e 3]
+		for {} {$c > 0} {incr c -1} {
+		    $ctext insert end "-$filelines($p,$f,$ol)\n" m$bestpn
+		    incr ol
+		}
+		set nl [lindex $e 1]
+		for {} {$l < $nl} {incr l} {
+		    $ctext insert end "+$filelines($id,$f,$l)\n" mresult
+		}
+	    }
+	}
+	for {} {$l < $endl} {incr l} {
 	    $ctext insert end "+$filelines($id,$f,$l)\n" $ncol
-	    incr l
 	}
-	set i $j
     }
     while {$l < $grouplineend} {
 	$ctext insert end " $filelines($id,$f,$l)\n"
@@ -2167,6 +2205,45 @@ proc processgroup {} {
     $ctext conf -state disabled
 }
 
+proc similarity {pnum l nlc f events} {
+    global diffmergeid parents diffoffset filelines
+
+    set id $diffmergeid
+    set p [lindex $parents($id) $pnum]
+    set ol [expr {$l + $diffoffset($p)}]
+    set endl [expr {$l + $nlc}]
+    set same 0
+    set diff 0
+    foreach e $events {
+	if {[lindex $e 2] != $pnum} continue
+	set nl [lindex $e 0]
+	set ol [expr {$ol + $nl - $l}]
+	for {} {$l < $nl} {incr l} {
+	    incr same [string length $filelines($id,$f,$l)]
+	    incr same
+	}
+	set oc [lindex $e 3]
+	for {} {$oc > 0} {incr oc -1} {
+	    incr diff [string length $filelines($p,$f,$ol)]
+	    incr diff
+	    incr ol
+	}
+	set nl [lindex $e 1]
+	for {} {$l < $nl} {incr l} {
+	    incr diff [string length $filelines($id,$f,$l)]
+	    incr diff
+	}
+    }
+    for {} {$l < $endl} {incr l} {
+	incr same [string length $filelines($id,$f,$l)]
+	incr same
+    }
+    if {$same == 0} {
+	return 0
+    }
+    return [expr {200 * $same / (2 * $same + $diff)}]
+}
+
 proc startdiff {ids} {
     global treediffs diffids treepending diffmergeid