gitk: Synchronize highlighting in file view when scrolling diff

Whenever the diff pane scrolls, highlight the corresponding file in the
file list on the right.  For a large commit with many files and long
per-file diffs, this makes it easier to keep track of what you're looking
at.

This allows simplifying the prevfile and nextfile functions, because
all they have to do is scroll the diff pane.

In some situations we want to suppress this mechanism, for example when
clicking on a file in the file list to select it, or when searching in the
diff, in which case we want to highlight based on the current search hit
and not the top line visible. In these cases it's not sufficient to set
a "suppress" flag before scrolling and reset it afterwards, because the
scrolltext notification is sent deferred from a timer or some such; so we
need to remember the scroll position for which we want to suppress the
auto-highlighting until the next call to scrolltext; a bit ugly, but does
the job.

Signed-off-by: Stefan Haller <stefan@haller-berlin.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -3309,6 +3309,7 @@ proc sel_flist {w x y} {
     } else {
 	catch {$ctext yview [lindex $difffilestart [expr {$l - 2}]]}
     }
+    suppress_highlighting_file_for_current_scrollpos
 }
 
 proc pop_flist_menu {w X Y x y} {
@@ -7947,32 +7948,42 @@ proc changediffdisp {} {
     $ctext tag conf dresult -elide [lindex $diffelide 1]
 }
 
-proc highlightfile {loc cline} {
+proc highlightfile {cline} {
-    global ctext cflist cflist_top
+    global cflist cflist_top
 
-    $ctext yview $loc
     $cflist tag remove highlight $cflist_top.0 "$cflist_top.0 lineend"
     $cflist tag add highlight $cline.0 "$cline.0 lineend"
     $cflist see $cline.0
     set cflist_top $cline
 }
 
+proc highlightfile_for_scrollpos {topidx} {
+    global difffilestart
+
+    if {![info exists difffilestart]} return
+
+    set top [lindex [split $topidx .] 0]
+    if {$difffilestart eq {} || $top < [lindex $difffilestart 0]} {
+	highlightfile 0
+    } else {
+	highlightfile [expr {[bsearch $difffilestart $top] + 2}]
+    }
+}
+
 proc prevfile {} {
     global difffilestart ctext cmitmode
 
     if {$cmitmode eq "tree"} return
     set prev 0.0
-    set prevline 1
     set here [$ctext index @0,0]
     foreach loc $difffilestart {
 	if {[$ctext compare $loc >= $here]} {
-	    highlightfile $prev $prevline
+	    $ctext yview $prev
 	    return
 	}
 	set prev $loc
-	incr prevline
     }
-    highlightfile $prev $prevline
+    $ctext yview $prev
 }
 
 proc nextfile {} {
@@ -7980,11 +7991,9 @@ proc nextfile {} {
 
     if {$cmitmode eq "tree"} return
     set here [$ctext index @0,0]
-    set line 1
     foreach loc $difffilestart {
-	incr line
 	if {[$ctext compare $loc > $here]} {
-	    highlightfile $loc $line
+	    $ctext yview $loc
 	    return
 	}
     }
@@ -8046,6 +8055,8 @@ proc incrsearch {name ix op} {
 	set here [$ctext search $searchdirn -- $searchstring anchor]
 	if {$here ne {}} {
 	    $ctext see $here
+	    suppress_highlighting_file_for_current_scrollpos
+	    highlightfile_for_scrollpos $here
 	}
 	searchmarkvisible 1
     }
@@ -8071,6 +8082,8 @@ proc dosearch {} {
 	    return
 	}
 	$ctext see $match
+	suppress_highlighting_file_for_current_scrollpos
+	highlightfile_for_scrollpos $match
 	set mend "$match + $mlen c"
 	$ctext tag add sel $match $mend
 	$ctext mark unset anchor
@@ -8097,6 +8110,8 @@ proc dosearchback {} {
 	    return
 	}
 	$ctext see $match
+	suppress_highlighting_file_for_current_scrollpos
+	highlightfile_for_scrollpos $match
 	set mend "$match + $ml c"
 	$ctext tag add sel $match $mend
 	$ctext mark unset anchor
@@ -8137,8 +8152,25 @@ proc searchmarkvisible {doall} {
     }
 }
 
+proc suppress_highlighting_file_for_current_scrollpos {} {
+    global ctext suppress_highlighting_file_for_this_scrollpos
+
+    set suppress_highlighting_file_for_this_scrollpos [$ctext index @0,0]
+}
+
 proc scrolltext {f0 f1} {
-    global searchstring
+    global searchstring cmitmode ctext
+    global suppress_highlighting_file_for_this_scrollpos
+
+    if {$cmitmode ne "tree"} {
+	set topidx [$ctext index @0,0]
+	if {![info exists suppress_highlighting_file_for_this_scrollpos]
+	    || $topidx ne $suppress_highlighting_file_for_this_scrollpos} {
+	    highlightfile_for_scrollpos $topidx
+	}
+    }
+
+    catch {unset suppress_highlighting_file_for_this_scrollpos}
 
     .bleft.bottom.sb set $f0 $f1
     if {$searchstring ne {}} {