bug#32795: Acknowledgement (26.1; provided-mode-derived-p does not support parent modes set with defalias)

[Andrew Schwartzmeyer]

Hi all,

I actually just found _another_ scenario that breaks due to this. I was 
editing a Jenkinsfile (groovy-mode) and expecting dtrt-indent to 
automatically adjust the indent, but it was not. Turns out it's the same 
reason again!

https://github.com/jscheid/dtrt-indent/blob/e860db7235147ed5ac1fd8f12b51dbb7cf2e75f1/dtrt-indent.el#L207

    (define-globalized-minor-mode dtrt-indent-global-mode 
dtrt-indent-mode
      (lambda ()
        (when (derived-mode-p 'prog-mode 'text-mode)
    (dtrt-indent-mode))))

The check `(derived-mode-p 'prog-mode 'text-mode)` returns nil, because 
the mode that groovy-mode derived from is set up like this:

    (defalias 'groovy-parent-mode
      (if (fboundp 'prog-mode) 'prog-mode 'fundamental-mode))

Using this for `provided-mode-derived-p` fixes it:

    (defun provided-mode-derived-p (mode &rest modes)
      "Non-nil if MODE is derived from one of MODES.
    Uses the `derived-mode-parent' property of the symbol to trace 
backwards.
    If you just want to check `major-mode', use `derived-mode-p'."
      (while
          (and
           (not (memq mode modes))
           (let* ((parent (get mode 'derived-mode-parent))
                  (parentfn (symbol-function parent)))
             (setq mode (if (and parentfn (symbolp parentfn)) parentfn 
parent)))))
      mode)

Thanks Robert Pluim for the `let*` trick, I was wondering how you do 
that without nesting `let` expressions.

Does anyone have other suggestions before I send a patch file?

Thanks,

Andy

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