bug#55038: 29.0.50; Does macroexp-file-name return nil unnecessarily?

bug#55038: 29.0.50; Does macroexp-file-name return nil unnecessarily?

[Philip Kaludercic]

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Consider a macro like

        (defmacro foo ()
          `(message "Defined in %s" ,(macroexp-file-name)))

Why does this expand to

        (message "Defined in %s" nil)

when evaluated directly in a file (say using `eval-buffer' or
`eval-last-sexp`).  Shouldn't it be fair to return the file name of the
buffer, if nothing else can be used:


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diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
index e4bc2df280..5df9d4b221 100644
--- a/lisp/emacs-lisp/macroexp.el
+++ b/lisp/emacs-lisp/macroexp.el
@@ -143,7 +143,8 @@ macroexp-file-name
   ;; so prefer using it over using `load-file-name'.
   (let ((file (car (last current-load-list))))
     (or (if (stringp file) file)
-        (bound-and-true-p byte-compile-current-file))))
+        (bound-and-true-p byte-compile-current-file)
+        (buffer-file-name))))
 
 (defvar macroexp--warned (make-hash-table :test #'equal :weakness 'key))
 

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Or is there something that would go wrong in that case?


In GNU Emacs 29.0.50 (build 6, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo version 1.16.0)
 of 2022-04-19 built on viero
Repository revision: d168decab4a03cd48b8b96257c36ffa575c720e6
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
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-- 
	Philip Kaludercic

bug#55038: 29.0.50; Does macroexp-file-name return nil unnecessarily?

[Lars Ingebrigtsen]

Philip Kaludercic <philipk@posteo.net> writes:

> Consider a macro like
>
>         (defmacro foo ()
>           `(message "Defined in %s" ,(macroexp-file-name)))
>
> Why does this expand to
>
>         (message "Defined in %s" nil)
>
> when evaluated directly in a file (say using `eval-buffer' or
> `eval-last-sexp`).  Shouldn't it be fair to return the file name of the
> buffer, if nothing else can be used:

[...]

> Or is there something that would go wrong in that case?

Such a change sounds like a good one to me, but perhaps there's a good
reason it works the way it does today.  Perhaps Stefan has a comment;
added to the CCs.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#55038: 29.0.50; Does macroexp-file-name return nil unnecessarily?

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> Consider a macro like
>
>         (defmacro foo ()
>           `(message "Defined in %s" ,(macroexp-file-name)))
>
> Why does this expand to
>
>         (message "Defined in %s" nil)
>
> when evaluated directly in a file (say using `eval-buffer' or
> `eval-last-sexp`).

No good reason.

> Shouldn't it be fair to return the file name of the buffer, if nothing
> else can be used:

In the case the code comes from the current buffer, yes.
OTOH if it comes from (say) `M-:`, no.

> diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
> index e4bc2df280..5df9d4b221 100644
> --- a/lisp/emacs-lisp/macroexp.el
> +++ b/lisp/emacs-lisp/macroexp.el
> @@ -143,7 +143,8 @@ macroexp-file-name
>    ;; so prefer using it over using `load-file-name'.
>    (let ((file (car (last current-load-list))))
>      (or (if (stringp file) file)
> -        (bound-and-true-p byte-compile-current-file))))
> +        (bound-and-true-p byte-compile-current-file)
> +        (buffer-file-name))))

I think we need to make `eval-buffer` and friends set a variable to
indicate when `buffer-file-name` can be used.


        Stefan