git-gui: Refresh a file if it has an empty diff.

When the user has enabled the Trust File Modification Timestamp option
then we may display a file as being modified yet that file may not have
a difference.  When the user clicks on that file we wind up displaying
an empty diff viewer, which makes no sense to the user.

So instead if we get an empty diff and the user has this option enabled
and the file's current state is _M (no change in index but the working
file appears modified) then run a quick update-index on just that file
and remove it from the list of modified files.  We also give the user
a quick dialog stating we are removing it, and why.

Usually I don't run into this situation when I have the Trust File
Modification Timestamp option enabled, so its not that annoying to
have a dialog pop open to remind me why there are no differences.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui

@@ -88,6 +88,25 @@ proc error_popup {msg} {
 		-message $msg
 }
 
+proc info_popup {msg} {
+	global gitdir appname
+
+	set title $appname
+	if {$gitdir != {}} {
+		append title { (}
+		append title [lindex \
+			[file split [file normalize [file dirname $gitdir]]] \
+			end]
+		append title {)}
+	}
+	tk_messageBox \
+		-parent . \
+		-icon error \
+		-type ok \
+		-title $title \
+		-message $msg
+}
+
 ######################################################################
 ##
 ## repository setup
@@ -204,7 +223,12 @@ proc update_status {{final Ready.}} {
 	} else {
 		set status_active 1
 		set ui_status_value {Refreshing file status...}
-		set fd_rf [open "| git update-index -q --unmerged --refresh" r]
+		set cmd [list git update-index]
+		lappend cmd -q
+		lappend cmd --unmerged
+		lappend cmd --ignore-missing
+		lappend cmd --refresh
+		set fd_rf [open "| $cmd" r]
 		fconfigure $fd_rf -blocking 0 -translation binary
 		fileevent $fd_rf readable \
 			[list update_status_stage2 $fd_rf $final]
@@ -381,6 +405,42 @@ proc reshow_diff {} {
 	}
 }
 
+proc handle_empty_diff {} {
+	global ui_fname_value file_states file_lists
+
+	set path $ui_fname_value
+	set s $file_states($path)
+	if {[lindex $s 0] != {_M}} return
+
+	info_popup "No differences detected.
+
+[short_path $path] has no changes.
+
+The modification date of this file was updated by another
+application and you currently have the Trust File Modification
+Timestamps feature enabled, so Git did not automatically detect
+that there are no content differences in this file.
+
+This file will now be removed from the modified files list, to
+prevent possible confusion.
+"
+	if {[catch {exec git update-index -- $path} err]} {
+		error_popup "Failed to refresh index:\n\n$err"
+	}
+
+	clear_diff
+	set old_w [mapcol [lindex $file_states($path) 0] $path]
+	set lno [lsearch -sorted $file_lists($old_w) $path]
+	if {$lno >= 0} {
+		set file_lists($old_w) \
+			[lreplace $file_lists($old_w) $lno $lno]
+		incr lno
+		$old_w conf -state normal
+		$old_w delete $lno.0 [expr $lno + 1].0
+		$old_w conf -state disabled
+	}
+}
+
 proc show_diff {path {w {}} {lno {}}} {
 	global file_states file_lists
 	global PARENT diff_3way diff_active
@@ -451,6 +511,7 @@ proc show_diff {path {w {}} {lno {}}} {
 
 proc read_diff {fd} {
 	global ui_diff ui_status_value diff_3way diff_active
+	global cfg_trust_mtime
 
 	while {[gets $fd line] >= 0} {
 		if {[string match {diff --git *} $line]} continue
@@ -497,6 +558,10 @@ proc read_diff {fd} {
 		set diff_active 0
 		unlock_index
 		set ui_status_value {Ready.}
+
+		if {$cfg_trust_mtime && [$ui_diff index end] == {2.0}} {
+			handle_empty_diff
+		}
 	}
 }
 
@@ -588,7 +653,7 @@ before committing.
 		U? {
 			error_popup "Unmerged files cannot be committed.
 
-File [escape_path $path] has merge conflicts.
+File [short_path $path] has merge conflicts.
 You must resolve them and include the file before committing.
 "
 			unlock_index
@@ -597,7 +662,7 @@ You must resolve them and include the file before committing.
 		default {
 			error_popup "Unknown file state [lindex $s 0] detected.
 
-File [escape_path $path] cannot be committed by this program.
+File [short_path $path] cannot be committed by this program.
 "
 		}
 		}
@@ -888,6 +953,10 @@ proc escape_path {path} {
 	return $path
 }
 
+proc short_path {path} {
+	return [escape_path [lindex [file split $path] end]]
+}
+
 set next_icon_id 0
 
 proc merge_state {path new_state} {
@@ -921,7 +990,6 @@ proc merge_state {path new_state} {
 }
 
 proc display_file {path state} {
-	global ui_index ui_other
 	global file_states file_lists status_active
 
 	set old_m [merge_state $path $state]