Magit selections with shift-selection-mode on and transient-mark-mode off

[farblos]

Magit

Magit 20240311.1442 [>= 3.3.0.50-git], Transient 0.5.3, Git 2.43.0, Emacs 29.2, gnu/linux

Emacs

GNU Emacs 29.2 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo version 1.18.0, Xaw3d scroll bars) of 2024-02-27, modified by Debian

Description

Magit selections (in staged or unstaged diffs, for example) behave somewhat surpirsingly when shift-selection-mode is on and transient-mark-mode off. From a previous discussion with Eli I understood that this is a slightly undersupported feature in Emacs in general, so I'd like to double-check here before opening an issue.

Reproducer

• Start emacs -Q, M-: (package-activate-all) RET

• C-u C-x g <some-Git-controlled-directory> RET

• Visit some staged or unstaged changes, press S-<down> on some diff:

  Point does not move (expected), Magit selection is displayed (expected)

• C-g (to get rid of the active region)

• M-x transient-mark-mode RET

• Press S-<down> on some diff:

  Message Mark set (expected), point does not move (expected),
  Magit selection is not displayed (not expected)

Only on second S-<down> does the Magit selection show up.

Educated Guess

I think that at the point in time when the Magit selection is handled (post-command-hook)
the shift-selection code has not yet set up this temporary transient mark mode, so that
region-active-p still returns nil.

I can try to follow up, but please let me know first if there is a general interest in getting this
fixed...

[tarsius]

Magit uses specialized previous-/next-line commands to deal with shift-selection. What those do might not be the best they could do. First see the docstring of magit-next-line.

Message Mark set (expected), point does not move (expected),

Why is the latter expected by you? The first next-line does move to the next line, even when using shift-selection. The magit commands prevent that because the region works a bit differently as explained in the mentioned docstrings.

As a quick check I replaced (push-mark nil nil t) with (handle-shift-selection) in these functions. Now sometimes it works, as Magit expects it: point does not move on the first invocation and the line is highlighted. But sometimes it does not: the line is also highlighted, but point moves.

Maybe, after some reading and with the help of some debug statements, I can find a way to make it always work as intended. I am very very busy right now, so I won't do that soon.

As a workaround I believe you can move down an additional line and then up again; then the single, selected line is highlighted as expected.

[farblos]

I am very very busy right now, so I won't do that soon.

That's fine, thanks for the quick reply.

At least I understood that there is at least some general interest in handling this case, and so I also might try to investigate here ...