gitk: added external diff file rename detection

* If a file was renamed between commits and an external diff is started
  through gitk on the original or the renamed file name,
  gitk was unable to open the renamed file in the external diff editor.
  It failed to fetch the renamed file from git, because it fetched it
  using its original path in contrast to using the renamed path of the
  file.
* With this change gitk detects the rename and opens the external diff
  with the original and the renamed file instead of no file (it is able
  to fetch the renamed file path and name now from git).
* Since git doesn't destinguish between move or rename this also works
  for moved files.
* Showing the external diff with the original and the renamed file
  works when either of the files is selected in gitk.

Signed-off-by: Tobias Boesch <[email protected]>

Author: ToBoMi

gitk-git/gitk

@@ -3806,6 +3806,39 @@ proc external_diff_get_one_file {diffid filename diffdir} {
                "revision $diffid"]
 }
 
+proc check_for_renames_in_diff {filepath} {
+    global ctext
+
+    set renamed_filenames [list {}]
+    set filename [file tail $filepath]
+    set rename_from_text_identifier_length 12
+    set rename_to_text_identifier_length 10
+    set reg_expr_rename_from {^rename from (.*$filename)}
+    set reg_expr_rename_from [subst -nobackslashes -nocommands $reg_expr_rename_from]
+    set rename_from_text_index [$ctext search -elide -regexp -- $reg_expr_rename_from 0.0]
+    if { ($rename_from_text_index != {})} {
+        set reg_expr_rename_to {^rename to (.*)}
+        set rename_to_text_index [$ctext search -elide -regexp -- $reg_expr_rename_to $rename_from_text_index]
+        if { ($rename_from_text_index != {}) && ($rename_to_text_index != {}) } {
+            lappend renamed_filenames [$ctext get "$rename_from_text_index + $rename_from_text_identifier_length chars" "$rename_from_text_index lineend"]
+            lappend renamed_filenames [$ctext get "$rename_to_text_index + $rename_to_text_identifier_length chars" "$rename_to_text_index lineend"]
+        }
+        return $renamed_filenames
+    }
+    set reg_expr_rename_to {^rename to (.*$filename)}
+    set reg_expr_rename_to [subst -nobackslashes -nocommands $reg_expr_rename_to]
+    set rename_to_text_index [$ctext search -elide -regexp -- $reg_expr_rename_to 0.0]
+    if { ($rename_to_text_index != {})} {
+        set reg_expr_rename_from {^rename from (.*)}
+        set rename_from_text_index [$ctext search -backwards -elide -regexp -- $reg_expr_rename_from $rename_to_text_index]
+        if { ($rename_to_text_index != {}) && ($rename_from_text_index != {}) } {
+            lappend renamed_filenames [$ctext get "$rename_from_text_index + $rename_from_text_identifier_length chars" "$rename_from_text_index lineend"]
+            lappend renamed_filenames [$ctext get "$rename_to_text_index + $rename_to_text_identifier_length chars" "$rename_to_text_index lineend"]
+        }
+        return $renamed_filenames
+    }
+}
+
 proc external_diff {} {
     global nullid nullid2
     global flist_menu_file
@@ -3836,8 +3869,16 @@ proc external_diff {} {
     if {$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]
+    set renamed_filenames [check_for_renames_in_diff $flist_menu_file]
+    set rename_from_filename [lindex $renamed_filenames 1]
+    set rename_to_filename [lindex $renamed_filenames 2]
+    if { ($rename_from_filename != {}) && ($rename_to_filename != {}) } {
+        set difffromfile [external_diff_get_one_file $diffidfrom $rename_from_filename $diffdir]
+        set difftofile [external_diff_get_one_file $diffidto $rename_to_filename $diffdir]
+    } else {
+        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]