Buffer local example transient-with-shadowed-buffer

[psionic-k]

Waiting until I can use 5.2.0+ because of the seq 2.24+ requirement

This is about buffer locals and the current-buffer during suffixes

[psionic-k]

I determined that the current version of transient is setting the current buffer properly at every predicate, :info or :description that I could find, so it seems no further examples are necessary and explicit use of `transient--shadowed-buffer' is not necessary.

In practice, current-buffer always returned the same value as transient--shadowed-buffer, so I was unable to demonstrate any situation where current-buffer would point to the transient's UI buffer.

Example code works, but is fine with either current-buffer or transient--shadowed-buffer

** Accessing the Source Buffer
This section is about using the buffer from which you called the transient and its [[info:elisp#Buffer-Local Variables][Buffer-Local Variables]].

Some code you use to customize a transient /might/ be evaluated in the context of the transient's UI buffer.  If you instead want to access the buffer from which you called the transient, check the value of =transient--shadowed-buffer=.  It may differ from the value returned by ~current-buffer~.

The docstring for =transient--shadowed-buffer= states:
#+begin_quote
This is bound while the suffix predicate is being evaluated and while drawing in the transient buffer.
#+end_quote
This means predicates such as the =:if= slot.

⚠️ To quickly evaluate code in the source buffer, you probably want to use ~with-current-buffer~ instead of ~set-buffer~ to avoid leaving the wrong buffer active when your custom code returns to transient.

#+begin_src elisp :tangle transient-showcase.el :var _=wave-prelude
  (defun tsc--shadowed-buffer-org-mode-p ()
    "Return t if major mode of shadowed buffer derives from `org-mode'."
    (and transient--shadowed-buffer
         (provided-mode-derived-p
          (buffer-local-value 'major-mode transient--shadowed-buffer)
          '(org-mode))))

  (defun tsc--shadowed-buffer-elisp-mode-p ()
    "Return t if major mode of shadowed buffer derives from `emacs-lisp-mode'."
    (and transient--shadowed-buffer
         (provided-mode-derived-p
          (buffer-local-value 'major-mode transient--shadowed-buffer)
          '(emacs-lisp-mode))))

  (defun tsc--current-buffer-name ()
    (current-buffer))

  (defun tsc--shadowed-buffer-name ()
    (if transient--shadowed-buffer
        (buffer-name transient--shadowed-buffer)
      "`transient--shadowed-buffer' was nil."))

  (transient-define-prefix tsc-shadowed-buffer ()
    "Display Mode-Specific Commands Based"
    [["Org Mode Commands"
      :if tsc--shadowed-buffer-org-mode-p
      ("o" "org mode wave" tsc-suffix-wave)]
     ["Elisp Mode Commands"
      :if tsc--shadowed-buffer-elisp-mode-p
      ("e" "elisp mode wave" tsc-suffix-wave)]])
#+end_src