[PATCH v4] gitk: Use git-difftool for external diffs

[David Aguilar <davvid@gmail.com>]

This teaches gitk about git-difftool.  A benefit of this change
is that gitk's external diff feature now works with read-only
repositories.

Signed-off-by: David Aguilar <davvid@gmail.com>
---
 gitk |   58 ++++++++--------------------------------------------------
 1 files changed, 8 insertions(+), 50 deletions(-)

diff --git a/gitk b/gitk
index 1f36a3e..71cb501 100755
--- a/gitk
+++ b/gitk
@@ -3317,39 +3317,6 @@ proc gitknewtmpdir {} {
     return $diffdir
 }
 
-proc save_file_from_commit {filename output what} {
-    global nullfile
-
-    if {[catch {exec git show $filename -- > $output} err]} {
-	if {[string match "fatal: bad revision *" $err]} {
-	    return $nullfile
-	}
-	error_popup "[mc "Error getting \"%s\" from %s:" $filename $what] $err"
-	return {}
-    }
-    return $output
-}
-
-proc external_diff_get_one_file {diffid filename diffdir} {
-    global nullid nullid2 nullfile
-    global gitdir
-
-    if {$diffid == $nullid} {
-        set difffile [file join [file dirname $gitdir] $filename]
-	if {[file exists $difffile]} {
-	    return $difffile
-	}
-	return $nullfile
-    }
-    if {$diffid == $nullid2} {
-        set difffile [file join $diffdir "\[index\] [file tail $filename]"]
-        return [save_file_from_commit :$filename $difffile index]
-    }
-    set difffile [file join $diffdir "\[$diffid\] [file tail $filename]"]
-    return [save_file_from_commit $diffid:$filename $difffile \
-	       "revision $diffid"]
-}
-
 proc external_diff {} {
     global nullid nullid2
     global flist_menu_file
@@ -3375,24 +3342,15 @@ proc external_diff {} {
         set diffidto [lindex $diffids 1]
     }
 
-    # make sure that several diffs wont collide
-    set diffdir [gitknewtmpdir]
-    if {$diffdir eq {}} return
-
-    # gather files to diff
-    set difffromfile [external_diff_get_one_file $diffidfrom $flist_menu_file $diffdir]
-    set difftofile [external_diff_get_one_file $diffidto $flist_menu_file $diffdir]
-
-    if {$difffromfile ne {} && $difftofile ne {}} {
-        set cmd [list [shellsplit $extdifftool] $difffromfile $difftofile]
-        if {[catch {set fl [open |$cmd r]} err]} {
-            file delete -force $diffdir
-            error_popup "$extdifftool: [mc "command failed:"] $err"
-        } else {
-            fconfigure $fl -blocking 0
-            filerun $fl [list delete_at_eof $fl $diffdir]
-        }
+    set cmd [list "git" "difftool" "--no-prompt" "--extcmd=$extdifftool"]
+    if {$diffidfrom ne $nullid && $diffidfrom ne $nullid2} {
+        lappend cmd $diffidfrom
+    }
+    if {$diffidto ne $nullid && $diffidto ne $nullid2} {
+        lappend cmd $diffidto
     }
+    lappend cmd "--" $flist_menu_file
+    eval exec $cmd &
 }
 
 proc find_hunk_blamespec {base line} {
-- 
1.7.0.3.313.g87b3c