[meld] filediff: Set buffers as modified when using custom save path (#581)

[Kai Willadsen <kaiw src gnome org>]

commit 603b13aba66f9b1e014b687bc73d5c14095f982d
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sat Jan 8 13:57:40 2022 +1000

    filediff: Set buffers as modified when using custom save path (#581)
    
    This change is about improving conflict resolution, which is envisaged
    as the primary use case for the `--output` flag. The point here is that
    if when you use the "save this buffer to a different place than where
    you loaded it from" functionality, it's reasonable to expect that the
    buffer is going to need to be saved in order for the buffer contents to
    end up on disk.
    
    This will change some workflows slightly, in that if you open up a
    conflict from Meld's version control view but make no changes, you'll
    now be prompted to save the file... but this seems like an acceptable
    trade-off.

 meld/filediff.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
---
diff --git a/meld/filediff.py b/meld/filediff.py
index 38420618..436fabf8 100644
--- a/meld/filediff.py
+++ b/meld/filediff.py
@@ -1604,9 +1604,17 @@ class FileDiff(Gtk.VBox, MeldDoc):
                 'dialog-warning-symbolic', primary, secondary, _("Open"),
                 functools.partial(open_files_external, gfiles=[gfile]))
 
+        # We checkpoint first, which will set modified state via the
+        # checkpointed callback. We then check whether we're saving the
+        # file to a different location than it was loaded from, in
+        # which case we assume that this needs to be saved to persist
+        # what the user is seeing. Finally, we update the writability,
+        # which does label calculation.
+        self.undosequence.checkpoint(buf)
+        if buf.data.savefile:
+            buf.set_modified(True)
         self.update_buffer_writable(buf)
 
-        self.undosequence.checkpoint(buf)
         buf.data.update_mtime()
         buf.data.loaded = True