Unable to use `ediff-region-wordwise/linewise`

[c02y]

Description :octocat:

When I try to use ediff-region-wordwise/linewise in vanilla emacs, emacs asks me to choose buffers and then mark one region, C-M-c, and mark another region, C-M-c again to ediff the regions. This works very well when I try it in emacs -q or emacs with my own init.el, but when I try it in spacemacs with even fresh installation, one of the two regions in ediff session is not right, it is empty or just part of what I marked. I recorded a gif. Sorry about that the keystrokes were not captured, but I did follow the instructions to hit the keystrokes.

Reproduction guide :beetle:

• Start Emacs
• Open a file containing the similar parts for ediff
• M-x ediff-region-wordwise # or M-x ediff-region-linewise
• choose the same buffer
• mark the first part using v or C-Space
• C-M-c as told
• mark the second part using v or C-Space
• C-M-c as told
• ediff session will be opened, check the two buffers in ediff session

Observed behaviour: :eyes: :broken_heart: One of the two buffers in ediff session is not right, it is empty or just part of what I marked

Expected behaviour: :heart: :smile: Two buffers in ediff session should be exactly what I marked.

System Info :computer:

• OS: gnu/linux
• Emacs: 26.2
• Spacemacs: 0.300.0
• Spacemacs branch: develop (rev. d8defccf7)
• Graphic display: t
• Distribution: spacemacs
• Editing style: vim
• Completion: helm
• Layers:

  (emacs-lisp helm multiple-cursors treemacs)

• System configuration features: XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS GLIB NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS XWIDGETS LIBSYSTEMD

Backtrace :paw_prints:

<<BACKTRACE IF RELEVANT>>

[duianto]

Confirmed.

The issue occurs when the dotspacemacs-distribution variable is set to 'spacemacs at the top of .spacemacs.

But it works as expected when it's set to 'spacemacs-base.

So there's some setting/package that causes it.

System Info :computer:

• OS: windows-nt
• Emacs: 26.2
• Spacemacs: 0.300.0
• Spacemacs branch: develop (rev. d6c8df3d0)
• Graphic display: t
• Distribution: spacemacs
• Editing style: vim
• Completion: helm
• Layers:

  (emacs-lisp git helm markdown multiple-cursors org treemacs version-control)

• System configuration features: XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS THREADS LCMS2

[Mikevin]

'spacemacs-base configures ediff like this

This could explain the difference.

[f380cedric]

On develop branch, commenting spacemacs-purpose in spacemacs/layers/+distributions/spacemacs/layers.el (line) does the trick. There is something to blame in the spacemacs-purpose layer.

[duianto]

@f380cedric Nice catch, it seems like it might be window-purpose related.

@bmag Do you know what could be going on here?

Two example functions:

    (defun clipboard/set (astring)
      "Copy a string to clipboard"
      (with-temp-buffer
        (insert astring)
        (clipboard-kill-region (point-min) (point-max))))

    (defun clipboard/get ()
      "Return the content of clipboard as string"
      (interactive)
      (with-temp-buffer
        (clipboard-yank)
        (buffer-substring-no-properties (point-min) (point-max))))

source: https://caiorss.github.io/Emacs-Elisp-Programming/Elisp_Snippets.html#sec-1-5

Reproduction steps

• Copy the two functions above.
• Open a new buffer SPC b N n.
• Paste the two functions p
• M-x ediff-regions-wordwise RET
• At the Region's A buffer: prompt, choose untitled, RET
• At the Region's B buffer: prompt, type un to highlight and choose untitled, RET
• Move the cursor to the first functions open parenthesis
• Start a selection by pressing v
• Jump to the matching parenthesis: %
• Mark the region: C-M-c
• Move the cursor to the second functions open parenthesis, There's a selection but it can't be canceled with Esc. (This is probably an ediff issue).
• Start a selection v
• Deselect v, now the initial selection is gone.
• Start a new selection v
• Jump to the matching parenthesis: %
• Mark the region: C-M-c
• Jumping to a diff hunk shows

Observed

With window-purpose (Spacemacs develop branch without any window-purpose changes)

ediff-regions-wordwise

The same steps above except by calling ediff-regions-linewise.

With window-purpose excluded (and Spacemacs restarted)

dotspacemacs-excluded-packages '(window-purpose)

ediff-regions-wordwise

ediff-regions-linewise

[bmag]

Thanks for the report and repro steps everyone. I looked into the matter and found that:

• the bug does not reproduce with vanilla Emacs and window-purpose, so it is not an upstream bug.
• the bug only reproduces when purpose-mode is enabled.
• the bug does not depend on Spacemacs configuration of ediff.
• the origin of the buggy behavior is in ediff-clone-buffer-for-region-comparison. The function is called twice to prompt the user for the desired regions, and the second call (for determining region B) somehow changes the region A (which was determined in the first call).

I wasn't able to find what causes the buggy behavior in ediff-clone-buffer-for-region-comparison, but I was to come up with a workaround. Put this in user-config, it disables purpose-mode during the call to ediff-clone-buffer-for-region-comparison:

(defun bm-adv-without-purpose (fn &rest args)
  (without-purpose (apply fn args)))
(advice-add #'ediff-clone-buffer-for-region-comparison :around #'bm-adv-without-purpose)

Are there any more buggy ediff commands other than ediff-region-wordwise/linewise?

[duianto]

Confirmed that snippet seems to fix it.

I tried a couple of the other ediff commands and they seem to work, it might just be the region commands that have this issue.

I'm getting an unrelated issue with ediff3, ediff-buffers3, ediff-files3 and ediff-merge

/usr/bin/diff3: diff failed:

Even though:

(executable-find "diff3")

returns:

"c:/tools/cygwin/bin/diff3.exe"

[github-actions[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Please let us know if this issue is still valid!

[c02y]

This bug seems fixed without the code snippet(bm-adv-without-purpose) posted by @bmag

[f380cedric]

Same here, seems fixed.

[duianto]

Confirmed, it seems to be working as expected without any changes.

Windows 1903, System Info (click to expand)

#### System Info :computer:
- OS: windows-nt
- Emacs: 27.1
- Spacemacs: 0.300.0
- Spacemacs branch: develop (rev. 76301564c)
- Graphic display: t
- Distribution: spacemacs
- Editing style: vim
- Completion: helm
- Layers:
```elisp
(emacs-lisp git helm lsp multiple-cursors org
            (python :variables python-backend 'lsp python-lsp-server 'mspyls)
            version-control treemacs)
```
- System configuration features: XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2 HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS JSON PDUMPER LCMS2 GMP