Re: changing tags-file-name

[Eli Zaretskii <eliz@gnu.org>]

> From: "James K. Lowden" <jklowden@speakeasy.net>
> Date: Tue, 5 Dec 2017 11:31:56 -0500
> 
> The name of the file AIUI is tags-file-name, which C-h v describes as: 
> 
> tags-file-name is a variable defined in ?etags.el?.
> Its value is
> "/home/jklowden/projects/3rd/libdwarf/code/dwarfgen/TAGS"
> 
>   This variable is safe as a file local variable if its value
>   satisfies the predicate ?stringp?.
> 
> Documentation:
> File name of tags table.
> To switch to a new tags table, setting this variable is sufficient.
> [...]
> 
> When I use M-x set-variable, it rejects tags-file-name.  For
> "tags-" completion it says, 
> 
> Possible completions are:
> tags-add-tables 	tags-apropos-additional-actions
> tags-apropos-verbose 	tags-case-fold-search
> tags-compression-info-list 	tags-loop-revert-buffers
> tags-revert-without-query 	tags-table-list
> tags-tag-face
> 
> Why would emacs display a variable name, document that setting is
> fine, and not be able to set it?  

set-variable only supports user options (a.k.a. "defcustoms").  For
other variables, use

  M-: (setq VAR VALUE) RET

> Is there an easier way to change the tags file name (or add one and
> drop one) that I'm overlooking? 

You are overlooking "M-x visit-tags-table RET", I think.