gitk: add external diff file rename detection

If a file is renamed between commits and an external diff is started
through gitk on the original or the renamed file name,
gitk is unable to open the renamed file in the external diff editor.
It fails to fetch the renamed file from git, because it fetches it
using its original path in contrast to using the renamed path of the
file.
Detect the rename and open the external diff with the original and
the renamed file instead of no file (fetch the renamed file path and
name from git) no matter if the original or the renamed file is
selected in gitk.
Since moved or renamed file are handled the same way do this also
for moved files.

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]