bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[HuangMario]

I'm using etags and found that:

Step 0. Set the 'tags-file-name' as buffer local to a specified TAGS file, and the global value is nil.

Step 1. Press M-. to find tags.

Step 2. Input some characters in the mini-buffer and press the TAB key for completion, then the mini-buffer will display "Making tags completion table for ...done".

After that, the global value of 'tags-file-name' is set to the same as its local value.

How can I keep the global value nil ?



In GNU Emacs 24.5.1 (x86_64-apple-darwin13.4.0, NS apple-appkit-1265.21)
of 2015-04-11 on builder10-9.porkrind.org
Windowing system distributor `Apple', version 10.3.1348
Configured using:
`configure --with-ns '--enable-locallisppath=/Library/Application
Support/Emacs/${version}/site-lisp:/Library/Application
Support/Emacs/site-lisp''

Important settings:
  locale-coding-system: utf-8-unix

Major mode: C/l

Minor modes in effect:
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  file-name-shadow-mode: t
  global-font-lock-mode: t
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Recent messages:
Undo! [3 times]
Saving file /Users/mario/Documents/mcc/decl.c...
Wrote /Users/mario/Documents/mcc/decl.c
(No files need saving)
Compilation finished
Mark set
Saving file /Users/mario/Documents/mcc/decl.c...
Wrote /Users/mario/Documents/mcc/decl.c
(No files need saving)
Compilation finished

Load-path shadows:
None found.

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bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[Eli Zaretskii]

> From: HuangMario <guiyang.huang@me.com>
> Date: Wed, 09 Sep 2015 21:18:04 +0800
> 
> Step 0. Set the 'tags-file-name' as buffer local to a specified TAGS file, and the global value is nil.
> 
> Step 1. Press M-. to find tags.
> 
> Step 2. Input some characters in the mini-buffer and press the TAB key for completion, then the mini-buffer will display "Making tags completion table for ...done".
> 
> After that, the global value of 'tags-file-name' is set to the same as its local value.
> 
> How can I keep the global value nil ?

According to this doc string:

  (defun visit-tags-table (file &optional local)
    "Tell tags commands to use tags table file FILE.
  FILE should be the name of a file created with the `etags' program.
  A directory name is ok too; it means file TAGS in that directory.

  Normally \\[visit-tags-table] sets the global value of `tags-file-name'.
  With a prefix arg, set the buffer-local value instead.

you are supposed to invoke visit-tags-table manually with a numeric
argument, if you want the local value of tags-file-name set.

bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[Dmitry Gutov]

On 09/10/2015 10:06 PM, Eli Zaretskii wrote:

> you are supposed to invoke visit-tags-table manually with a numeric
> argument, if you want the local value of tags-file-name set.

Some users prefer to set tags-table-name programmatically.

It appears the problem is that etags--xref-find-definitions calls 
visit-tags-table-buffer unconditionally, and the latter doesn't honor 
the buffer-local value of this variable.

bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[Eli Zaretskii]

> Cc: 21443@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Fri, 11 Sep 2015 03:30:48 +0300
> 
> On 09/10/2015 10:06 PM, Eli Zaretskii wrote:
> 
> > you are supposed to invoke visit-tags-table manually with a numeric
> > argument, if you want the local value of tags-file-name set.
> 
> Some users prefer to set tags-table-name programmatically.
> 
> It appears the problem is that etags--xref-find-definitions calls 
> visit-tags-table-buffer unconditionally, and the latter doesn't honor 
> the buffer-local value of this variable.

The OP was talking about Emacs 24.5; there's no xref there AFAIK.

bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[Eli Zaretskii]

> Date: Fri, 11 Sep 2015 14:09:53 +0800 (CST)
> From: HGY <mohu3g@163.com>
> 
> As you say, how can I inhiit the mini-buffer completion to invoke
> 'visit-tags-table' with no prefix arg in step 2 ?

You can't, currently.  You need to invoke visit-tags-table manually,
with a prefix argument, before the mini-buffer completion.  This is
how the code was designed.

bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[Dmitry Gutov]

On 09/11/2015 07:56 AM, Eli Zaretskii wrote:

> The OP was talking about Emacs 24.5; there's no xref there AFAIK.

Right, sorry, there's no xref there.

But the scenario is similar: tags-completion-table calls 
visit-tags-table-buffer, and the latter doesn't honor buffer-local values.

bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[HGY]

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Yeah, I think so.


Best Regards.

Guiyang Huang






在2015年09月11 21时59分, "Dmitry Gutov"<dgutov@yandex.ru>写道:

On 09/11/2015 07:56 AM, Eli Zaretskii wrote:

> The OP was talking about Emacs 24.5; there's no xref there AFAIK.

Right, sorry, there's no xref there.

But the scenario is similar: tags-completion-table calls
visit-tags-table-buffer, and the latter doesn't honor buffer-local values.




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bug#21443: 24.5; etags' complete-tag changes the global value of tags-file-name

[Dmitry Gutov]

On 09/11/2015 09:57 AM, Eli Zaretskii wrote:

> You can't, currently.  You need to invoke visit-tags-table manually,
> with a prefix argument, before the mini-buffer completion.  This is
> how the code was designed.

Unfortunately, this is also broken: you can C-u M-x visit-tags-table, 
and it will set the local value of tags-file-name, but as soon as you 
M-x find-tag, it changes the global value of tags-file-name as well, to 
the last element in tags-table-list.

Apparently because the lambda in tags-lazy-completion-table calls 
visit-tags-table-buffer at least twice, and the latter function modifies 
tags-file-name, _and_ changes the current buffer (and when called the 
second time, it changes tags-file-name in the tags table buffer, thus 
changing the global value).

And I can't simply wrap most of the second half of 
visit-tags-table-buffer in a with-current-buffer, because some code 
assumes that the buffer does indeed change. Otherwise, the value of 
tags-completion-table-function is nil (tags-completion-table calls it 
after calling visit-tags-table-buffer).

Modifications of tags-file-name are also numerous, so changing a couple 
of setq to setq-local inside visit-tags-table-buffer doesn't do the 
trick either.

At this point I'm leaving this to someone else who's more motivated. But 
we'll likely already migrate to e.g. GNU Global before that happens.