Choosing tags tables

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Choosing tags tables

Daniel Lopez
Hi,

After more than a decade of Emacs use I thought I'd finally try out the
tags features. I regularly code in different languages so I'm gonna need
to call on different tags tables in different buffers. And I tend to use
libraries in each of those languages so I'll want to have more than one
tags table in each search, ie. that of the utility library/libraries and
that of the project I'm working on.

So I set it up so that for example in my c++-mode-hook it sets
tags-table-list with the multiple tags files I want to use for C++; the
first is the library I use in all my C++ projects and the second is the
project-specific tags file (assuming all project sources are in the same
directory as TAGS, for now). I'm setting it as buffer-local so that it
only applies to tag searches that are started when that buffer is current:

  (setq-local tags-table-list
    (list "/home/daniel/docs/code/c/reusable/checkout/dan/TAGS"
          (concat default-directory "TAGS")))

However when I then do a xref-find-definitions Emacs prompts me:
"Visit tags table (default TAGS):"
because (in visit-tags-table-buffer) it's not looking for the
buffer-local value of tags-table-list, only the global which is nil. If
I go along with it and enter something then Emacs sets tags-file-name to
my entry which means now I only have one tags file and my
tags-table-list gets ignored.

I alternatively tried this in my c++-mode-hook:

(visit-tags-table "/home/daniel/docs/code/c/reusable/checkout/dan/TAGS")
(visit-tags-table (concat default-directory "TAGS"))

but then whenever I open a file I get prompted about whether I want the
second one to replace the first or be appended in consideration. I don't
want to be prompted at all, I'd like to set most of this up in my init.
I might want to call up such prompts to tweak things later but it's not
likely.

Does anyone know of a better way to get this effect?

Regards,
Daniel

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Re: Choosing tags tables

Eli Zaretskii
> From: Daniel Lopez <[hidden email]>
> Date: Thu, 20 Jul 2017 04:17:23 +0100
>
> So I set it up so that for example in my c++-mode-hook it sets
> tags-table-list with the multiple tags files I want to use for C++; the
> first is the library I use in all my C++ projects and the second is the
> project-specific tags file (assuming all project sources are in the same
> directory as TAGS, for now). I'm setting it as buffer-local so that it
> only applies to tag searches that are started when that buffer is current:
>
>   (setq-local tags-table-list
>     (list "/home/daniel/docs/code/c/reusable/checkout/dan/TAGS"
>           (concat default-directory "TAGS")))
>
> However when I then do a xref-find-definitions Emacs prompts me:
> "Visit tags table (default TAGS):"
> because (in visit-tags-table-buffer) it's not looking for the
> buffer-local value of tags-table-list, only the global which is nil. If
> I go along with it and enter something then Emacs sets tags-file-name to
> my entry which means now I only have one tags file and my
> tags-table-list gets ignored.

I think this should be reported as a bug, using report-emacs-bug.

In your report, please provide more details about your conclusion that
visit-tags-table-buffer ignores buffer-local values: AFAICT, that
function does have provisions for considering local values, so it
could be that xref-find-definitions fails to invoke some functions
correctly or with the right buffer being the current one.  A Lisp
backtrace at the time visit-tags-table-buffer could help.

Also, a minimal test case to reproduce the problem will be useful.

> Does anyone know of a better way to get this effect?

The way you tried first should "just work".

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Re: Choosing tags tables

Dmitry Gutov
On 7/20/17 8:23 AM, Eli Zaretskii wrote:

> The way you tried first should "just work".

Only in master, right? Maybe Daniel is trying a release version of Emacs.

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Re: Choosing tags tables

Eli Zaretskii
> From: Dmitry Gutov <[hidden email]>
> Date: Thu, 20 Jul 2017 12:58:07 +0300
>
> On 7/20/17 8:23 AM, Eli Zaretskii wrote:
>
> > The way you tried first should "just work".
>
> Only in master, right?

Maybe, I'm not sure.  That's why I asked for a simple reproducer.

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Re: Choosing tags tables

Daniel Lopez
On 20/07/17 11:32, Eli Zaretskii wrote:

>> From: Dmitry Gutov <[hidden email]>
>> Date: Thu, 20 Jul 2017 12:58:07 +0300
>>
>> On 7/20/17 8:23 AM, Eli Zaretskii wrote:
>>
>>> The way you tried first should "just work".
>>
>> Only in master, right?
>
> Maybe, I'm not sure.  That's why I asked for a simple reproducer.
>
>

It's true, I'm using the current release version according to Arch Linux
which is 25.2.

I'll post a reproducer shortly to [hidden email].

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