Subject: bug#34765: 26.1; with-temp-buffer should not run buffer-list-update-hook

From: martin rudalics <[email-masked]>
Date: Thu, 23 May 2019 10:38:38 +0200

>> Thanks, I hope I understand it now.  Could you pretty please add the
 >> (instructive for me) "a buffer created when the reused buffer is busy
 >> and cannot be reused" somewhere to the comments maybe together with a
 >> reference to reused_workbuf_in_use.
 >
 > Not sure where you want to add this.  coding.c already says:

That's what I've read and did not understand.  It's a bit too concise.

 >    /* Name (or base name) of work buffer for code conversion.  */
 >    Lisp_Object Vcode_conversion_workbuf_name;

This comment insinuates that there is only one such buffer.

 >    /* A working buffer used by the top level conversion.

What is the "top level conversion"?

 >       Once it is
 >       created, it is never destroyed.  It has the name
 >       Vcode_conversion_workbuf_name.  The other working buffers are
 >       destroyed after the use is finished, and their names are modified
 >       versions of Vcode_conversion_workbuf_name.  */
 >    static Lisp_Object Vcode_conversion_reused_workbuf;
 >
 >    /* True iff Vcode_conversion_reused_workbuf is already in use.  */
 >    static bool reused_workbuf_in_use;
 >
 > is that what you wanted to see?

I'd prefer something like a common comment for all these variables
going as

/* The internal work buffers for code conversion are created lazily on
    demand.  The name of the first buffer created that way is specified
    by Vcode_conversion_workbuf_name.  Once created, this buffer is no
    more deleted in the current Emacs session.  While this buffer is in
    use, the boolean variable reused_workbuf_in_use is true.  This
    buffer is reused for new conversions whenever reused_workbuf_in_use
    is false.

    When reused_workbuf_in_use is true and more code conversion work
    has to be done, a new buffer is created.  The name of that new
    buffer is generated by Fgenerate_new_buffer_name, using
    Vcode_conversion_workbuf_name as base name.  Any such buffer is
    destroyed immediately as soon as it is no more used.  */

 >> Hopefully this also means that we can use _something like_
 >> Fgenerate_new_buffer to replace both instances of Fget_buffer_create
 >> in code_conversion_restore.
 >
 > You mean code_conversion_save, I presume.

You presume correctly.

 > One of those calls to Fget_buffer_create shouldn't generate a new
 > name, though.  It should always use a fixed name.

Fgenerate_new_buffer_name should do that: "If there is no live buffer
named NAME, then return NAME.".

Concludingly, what we need in the present context is a function

- to create a buffer whose name is generated from a base name
   argument,

- to set the new buffer's inhibit_buffer_hooks flag according to a
   corresponding argument and to not run any hooks when that flag
   should be set and the buffer is created,

- that is as internal as possible to avoid that applications misuse it
   (it can't be entirely internal since macros like 'with-temp-buffer'
   will need it).

martin