git-gui: Fix the after callback execution in rescan.

The rescan function receives a callback command
as its parameter, which is supposed to be executed
after the scan finishes. It is generally used to
update status. However, rescan may initiate a
loading of a diff, which always calls ui_ready after
completion. If the after handler is called before
that, ui_ready will override the new status.

This commit ensures that the after callback is
properly threaded through the diff machinery.

Since it uncovered the fact that force_first_diff
actually didn't work due to an undeclared global
variable, and the desired effects appeared only
because of the race condition between the diff
system and the rescan callback, I also reimplement
this function to make it behave as originally
intended.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -1491,10 +1491,8 @@ proc rescan_done {fd buf after} {
 	prune_selection
 	unlock_index
 	display_all_files
-	if {$current_diff_path ne {}} reshow_diff
-	if {$current_diff_path eq {}} select_first_diff
-
-	uplevel #0 $after
+	if {$current_diff_path ne {}} { reshow_diff $after }
+	if {$current_diff_path eq {}} { select_first_diff $after }
 }
 
 proc prune_selection {} {
@@ -2006,16 +2004,16 @@ proc do_rescan {} {
 }
 
 proc ui_do_rescan {} {
-	rescan {force_first_diff; ui_ready}
+	rescan {force_first_diff ui_ready}
 }
 
 proc do_commit {} {
 	commit_tree
 }
 
-proc next_diff {} {
+proc next_diff {{after {}}} {
 	global next_diff_p next_diff_w next_diff_i
-	show_diff $next_diff_p $next_diff_w {}
+	show_diff $next_diff_p $next_diff_w {} {} $after
 }
 
 proc find_anchor_pos {lst name} {
@@ -2100,25 +2098,42 @@ proc next_diff_after_action {w path {lno {}} {mmask {}}} {
 	}
 }
 
-proc select_first_diff {} {
+proc select_first_diff {after} {
 	global ui_workdir
 
 	if {[find_next_diff $ui_workdir {} 1 {^_?U}] ||
 	    [find_next_diff $ui_workdir {} 1 {[^O]$}]} {
-		next_diff
+		next_diff $after
+	} else {
+		uplevel #0 $after
 	}
 }
 
-proc force_first_diff {} {
-	global current_diff_path
+proc force_first_diff {after} {
+	global ui_workdir current_diff_path file_states
 
 	if {[info exists file_states($current_diff_path)]} {
 		set state [lindex $file_states($current_diff_path) 0]
+	} else {
+		set state {OO}
+	}
 
-		if {[string index $state 1] ne {O}} return
+	set reselect 0
+	if {[string first {U} $state] >= 0} {
+		# Already a conflict, do nothing
+	} elseif {[find_next_diff $ui_workdir $current_diff_path {} {^_?U}]} {
+		set reselect 1
+	} elseif {[string index $state 1] ne {O}} {
+		# Already a diff & no conflicts, do nothing
+	} elseif {[find_next_diff $ui_workdir $current_diff_path {} {[^O]$}]} {
+		set reselect 1
 	}
 
-	select_first_diff
+	if {$reselect} {
+		next_diff $after
+	} else {
+		uplevel #0 $after
+	}
 }
 
 proc toggle_or_diff {w x y} {

lib/diff.tcl

@@ -16,7 +16,7 @@ proc clear_diff {} {
 	$ui_workdir tag remove in_diff 0.0 end
 }
 
-proc reshow_diff {} {
+proc reshow_diff {{after {}}} {
 	global file_states file_lists
 	global current_diff_path current_diff_side
 	global ui_diff
@@ -30,13 +30,13 @@ proc reshow_diff {} {
 		|| [lsearch -sorted -exact $file_lists($current_diff_side) $p] == -1} {
 
 		if {[find_next_diff $current_diff_side $p {} {[^O]}]} {
-			next_diff
+			next_diff $after
 		} else {
 			clear_diff
 		}
 	} else {
 		set save_pos [lindex [$ui_diff yview] 0]
-		show_diff $p $current_diff_side {} $save_pos
+		show_diff $p $current_diff_side {} $save_pos $after
 	}
 }