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bug#21237: 25.0.50; defconst vs dump
From: |
Lars Ingebrigtsen |
Subject: |
bug#21237: 25.0.50; defconst vs dump |
Date: |
Wed, 09 Oct 2019 06:34:31 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) |
stephen_leake@stephe-leake.org writes:
> Given these two definitions:
>
> (defconst format-1
> (let ((str "(%s %s)"))
> (put-text-property 1 3 'face 'font-lock-keyword-face str)
> (put-text-property 4 6 'face 'font-lock-function-name-face str)
> str))
>
> (defvar format-2
> (let ((str "(%s %s %s)"))
> (put-text-property 1 3 'face 'font-lock-keyword-face str)
> (put-text-property 4 6 'face 'font-lock-function-name-face str)
> str))
>
> If I byte-compile a file containing these, and later load that
> byte-compiled file, the text properties are present on both format-1 and
> format-2.
>
> However, if the file is dumped for preloading into emacs, then the text
> properties are not present on format-1; the defconst apparently causes
> them to disappear.
I can confirm that this is still the case in Emacs 27.
> If this is desired/intended behavior, it should be documented in the
> defconst doc string, and there should be a warning during the dump
> process.
I tried looking around in the code a bit, but I don't really know what
to look for.
Does anybody know whether this behaviour is intended? It seems odd that
defvars and defconsts are handled differently here.
Hm... Oh! Here's from defconst:
if (!NILP (Vpurify_flag))
tem = Fpurecopy (tem);
and purecopy:
purecopy (Lisp_Object obj)
{
if (FIXNUMP (obj)
|| (! SYMBOLP (obj) && PURE_P (XPNTR (obj)))
|| SUBRP (obj))
return obj; /* Already pure. */
if (STRINGP (obj) && XSTRING (obj)->u.s.intervals)
message_with_string ("Dropping text-properties while making string `%s'
pure",
obj, true);
And, indeed, I get
Dropping text-properties while making string `(%s %s)' pure
when compiling. (Side issue: Should that have a "Warning: " prefix or
something so that it gets more noticeable?)
So I guess this is intended behaviour? I guess it's too obscure a thing
to put in the doc string of defconst.
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no
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