Hi,

I am writing to suggest a new feature to the ediff package that I think can
improve the user experience when resolving complicated merges.

It would be helpful if ediff supported switching between a 3 way diff
(i.e a diff between BASE, LOCAL & MASTER) and a diff with only the BASE
(i.e a
diff between just the BASE & LOCAL or a diff between just the BASE &
REMOTE).

While resolving a complicated merge I use
`ediff-merge-files-with-ancestor` to see all 3 versions (i.e BASE, LOCAL
& REMOTE) of the same file. In this setup ediff shows the diff by
comparing all 3 versions of the file.I often find it helpful to first
copy all the contents of the LOCAL buffer into the COMBINED buffer and
then view diff between REMOTE & BASE one by one and merge them correctly
inside the COMBINED buffer manually. (I ask git to not automerge such
files by using the `mergetool.hideResolved` flag so that I don't miss
any change). However, as far as I know there is no way to ask ediff to
only show the diff between the REMOTE BASE instead of
the default 3-way diff. It is bit cumbersome to jump over
the 3-way diff hunks and manually isolate the diff between REMOTE & BASE
from the 3-way diff between LOCAL, REMOTE & BASE.

I probably am uninformed about some existing feature that already does
this so feel free to point me towards that. If not, I would really like
to see this support from ediff.

Thank you
Amit



Emacs  : GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2020-06-16
Package: Ediff 2.81.5 of July 4, 2013

current state:
==============
(setq
 ediff-diff-program "diff"
 ediff-diff-options ""
 ediff-diff3-program "diff3"
 ediff-diff3-options ""
 ediff-patch-program "patch"
 ediff-patch-options "-f"
 ediff-shell "sh"
 ediff-use-faces t
 ediff-auto-refine 'on
 ediff-highlighting-style 'face
 ediff-buffer-A #<buffer layers_LOCAL_13445.go>
 ediff-buffer-B #<buffer layers_REMOTE_13445.go>
 ediff-control-buffer #<buffer *Ediff Control Panel*>
 ediff-forward-word-function 'ediff-forward-word
 ediff-control-frame nil
 ediff-control-frame-parameters '((name . "Ediff") (minibuffer)
(user-position . t) (vertical-scroll-bars) (scrollbar-width . 0)
 (scrollbar-height . 0) (menu-bar-lines . 0) (tool-bar-lines . 0)
(left-fringe . 0)
 (right-fringe . 0) (auto-lower) (auto-raise . t) (visibility) (width . 1)
(height . 1)
 (fullscreen) (top . 67) (left . 270))
 ediff-control-frame-position-function 'ediff-make-frame-position
 ediff-prefer-iconified-control-frame nil
 ediff-window-setup-function 'ediff-setup-windows-plain
 ediff-split-window-function 'split-window-horizontally
 ediff-job-name 'ediff-merge-files-with-ancestor
 ediff-word-mode nil
 ediff-buffer-name "*Ediff Control Panel*"
 ediff-device-type nil
 )