bug#54459: 29.0.50; Simplify connection-local variables (feature request)

bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Ergus via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Hi:

I use tramp very often and I find myself using this sort of snippet very
often:

(defvar-local gtags--executable 'unknown)

(defun gtags--executable ()
  (cond
   ((not (eq gtags--executable 'unknown)) ;; the value is already cached
    gtags--executable)
   ((file-remote-p default-directory)
    (with-connection-local-variables
     (if (boundp 'gtags--executable-connection)
         (setq-local gtags--executable gtags--executable-connection)

       ;; Else search and set as connection local for next uses.
       (setq-local gtags--executable (executable-find "gtags" t))
       (let* ((host (file-remote-p default-directory 'host))
              (symvars (intern (concat host "-gtags--vars")))) ;; profile name

         (connection-local-set-profile-variables
          symvars
          `((gtags--executable-connection . ,gtags--executable)))
         (connection-local-set-profiles `(:machine ,host) symvars))

       gtags--executable)))
   (t     ;; use default value (searched locally)
    (setq gtags--executable gtags-executable))))

The idea is that when using tramp with company it doesn't call
executable-find constantly in the remote buffers.

There are 3 issues that could be solved/improved:

1) If another buffer of a file in the same remote host is already open,
then when the function is called in that buffer for the first time it
will use the value cached in gtags--executable-connection. That's why in
the code I need to create a buffer local variable... Could we provide a
way to update all of them immediately?

2) There are functions to set connection-local profile variables
(connection-local-set-profile-variables) But so far there are not any
clean way to append variables to an existing profile; so a call to
connection-local-set-profile-variables deleted any previous variable,
actually the user is enforced to create a unique name for every profile
every time it needs something like this.

3) In the ideal world it may be possible to add an optional parameter to
tell executable-find to cache the found values per host and executable
name... so it could avoid the extra remote search... I understand this
shouldn't be enabled by default, but many packages may find it
useful. executable-find could be smart enough to remember some of the
previous searches at least in remote hosts.

Does it makes sense?



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 of 2022-03-18 built on Ergus
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bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Michael Albinus]

Ergus via "Bug reports for GNU Emacs, the Swiss army knife of text
editors" <bug-gnu-emacs@gnu.org> writes:

> Hi:

Hi,

> There are 3 issues that could be solved/improved:
>
> 1) If another buffer of a file in the same remote host is already open,
> then when the function is called in that buffer for the first time it
> will use the value cached in gtags--executable-connection. That's why in
> the code I need to create a buffer local variable... Could we provide a
> way to update all of them immediately?

I don't understand the scenario, sorry. Could you pls explain it in detail?

> 2) There are functions to set connection-local profile variables
> (connection-local-set-profile-variables) But so far there are not any
> clean way to append variables to an existing profile; so a call to
> connection-local-set-profile-variables deleted any previous variable,
> actually the user is enforced to create a unique name for every profile
> every time it needs something like this.

--8<---------------cut here---------------start------------->8---
(connection-local-set-profile-variables
 'profile
 (append
  (connection-local-get-profile-variables 'profile)
  my-variables-list))
--8<---------------cut here---------------end--------------->8---

> 3) In the ideal world it may be possible to add an optional parameter to
> tell executable-find to cache the found values per host and executable
> name... so it could avoid the extra remote search... I understand this
> shouldn't be enabled by default, but many packages may find it
> useful. executable-find could be smart enough to remember some of the
> previous searches at least in remote hosts.

That's hard to do. A user could change the remote PATH while the result
of executable-find is cached. Furthermore, Tramp appends the local part
of the remote default-directory to the directory search list. Therefore,
executable-find could return a possibly wrong cached value.

You could write your own function, using Tramp's cache mechanism, but at
your own risk. Something like (untested)

--8<---------------cut here---------------start------------->8---
(defun my-executable-find (command &optional remote)
  (if (and remote (file-remote-p default-directory))
      (with-tramp-connection-property
	  (tramp-get-process (tramp-dissect-file-name default-directory))
	  (concat "executable-find-" command)
	(executable-find command remote))
    (executable-find command remote)))
--8<---------------cut here---------------end--------------->8---

Best regards, Michael.

bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Ergus via Bug reports for GNU Emacs, the Swiss army knife of text editors]

On Sun, Mar 20, 2022 at 12:04:28PM +0100, Michael Albinus wrote:
>Ergus via "Bug reports for GNU Emacs, the Swiss army knife of text
>editors" <bug-gnu-emacs@gnu.org> writes:
>
>> Hi:
>
>Hi,
>
>> There are 3 issues that could be solved/improved:
>>
>> 1) If another buffer of a file in the same remote host is already open,
>> then when the function is called in that buffer for the first time it
>> will use the value cached in gtags--executable-connection. That's why in
>> the code I need to create a buffer local variable... Could we provide a
>> way to update all of them immediately?
>
>I don't understand the scenario, sorry. Could you pls explain it in detail?
>
Suppose:

C-x C-f /ssh:myhost:file1
C-x C-f /ssh:myhost:file2
(executable-find mycommand 1)
And here we set the connection local variable...

When we go to file1 if does not know about the variable in spite of it
is in the same host.

>> 2) There are functions to set connection-local profile variables
>> (connection-local-set-profile-variables) But so far there are not any
>> clean way to append variables to an existing profile; so a call to
>> connection-local-set-profile-variables deleted any previous variable,
>> actually the user is enforced to create a unique name for every profile
>> every time it needs something like this.
>
>--8<---------------cut here---------------start------------->8---
>(connection-local-set-profile-variables
> 'profile
> (append
>  (connection-local-get-profile-variables 'profile)
>  my-variables-list))
>--8<---------------cut here---------------end--------------->8---
>
Could you consider to add a snippet in the documentation explaining
this? Please?

>> 3) In the ideal world it may be possible to add an optional parameter to
>> tell executable-find to cache the found values per host and executable
>> name... so it could avoid the extra remote search... I understand this
>> shouldn't be enabled by default, but many packages may find it
>> useful. executable-find could be smart enough to remember some of the
>> previous searches at least in remote hosts.
>
>That's hard to do. A user could change the remote PATH while the result
>of executable-find is cached. Furthermore, Tramp appends the local part
>of the remote default-directory to the directory search list. 

SO this means that the executable in default-directory are also
considered? Like on Windows? I was not aware of that...

>Therefore,
>executable-find could return a possibly wrong cached value.
>
>You could write your own function, using Tramp's cache mechanism, but at
>your own risk. Something like (untested)
>
>--8<---------------cut here---------------start------------->8---
>(defun my-executable-find (command &optional remote)
>  (if (and remote (file-remote-p default-directory))
>      (with-tramp-connection-property
>	  (tramp-get-process (tramp-dissect-file-name default-directory))
>	  (concat "executable-find-" command)
>	(executable-find command remote))
>    (executable-find command remote)))
>--8<---------------cut here---------------end--------------->8---
>
I was thinking in something like:

(executable-find command &optional remote cache) but basically the same idea.

But it was just a dream... A man can dream, a man can dream ;p

>Best regards, Michael.

Thanks,
Ergus

bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Michael Albinus]

Ergus <spacibba@aol.com> writes:

Hi,

> Suppose:
>
> C-x C-f /ssh:myhost:file1
> C-x C-f /ssh:myhost:file2
> (executable-find mycommand 1)
> And here we set the connection local variable...
>
> When we go to file1 if does not know about the variable in spite of it
> is in the same host.

I recommend to move the code setting connection-local variables in a
funcion called by a hook, which is applied when visiting files in your
use case.

>>--8<---------------cut here---------------start------------->8---
>>(connection-local-set-profile-variables
>> 'profile
>> (append
>>  (connection-local-get-profile-variables 'profile)
>>  my-variables-list))
>>--8<---------------cut here---------------end--------------->8---
>>
> Could you consider to add a snippet in the documentation explaining
> this? Please?

Done in the Elisp manual, pushed to master as commit aec44a5be3.

>>That's hard to do. A user could change the remote PATH while the result
>>of executable-find is cached. Furthermore, Tramp appends the local part
>> of the remote default-directory to the directory search list.
>
> SO this means that the executable in default-directory are also
> considered? Like on Windows? I was not aware of that...

Well, this is rather an implementation detail, not documented. And I'm
not sure it is the best decision, we just needed a last element in
exec-path which is comparable to the last element in the local case of
exec-path.

>>You could write your own function, using Tramp's cache mechanism, but at
>>your own risk. Something like (untested)
>>
>>--8<---------------cut here---------------start------------->8---
>>(defun my-executable-find (command &optional remote)
>>  (if (and remote (file-remote-p default-directory))
>>      (with-tramp-connection-property
>>	  (tramp-get-process (tramp-dissect-file-name default-directory))
>>	  (concat "executable-find-" command)
>>	(executable-find command remote))
>>    (executable-find command remote)))
>>--8<---------------cut here---------------end--------------->8---
>>
> I was thinking in something like:
>
> (executable-find command &optional remote cache) but basically the same idea.

This cannot be generalized, the code uses Tramp specific functions. A
remote file name does not always mean invoking Tramp ...

> Thanks,
> Ergus

Best regards, Michael.

bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Michael Albinus]

Hi,

hmm, are there still open points? Otherwise I'd like to close the bug.

Best regards, Michael.

bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Ergus via Bug reports for GNU Emacs, the Swiss army knife of text editors]

On Tue, Mar 29, 2022 at 10:25:01AM +0200, Michael Albinus wrote:
>Hi,
>
>hmm, are there still open points? Otherwise I'd like to close the bug.
>
>Best regards, Michael.

As you added the documentation for it, please, close it then.

bug#54459: 29.0.50; Simplify connection-local variables (feature request)

[Michael Albinus]

Version: 29.1

Ergus <spacibba@aol.com> writes:

> On Tue, Mar 29, 2022 at 10:25:01AM +0200, Michael Albinus wrote:
>>Hi,
>>
>>hmm, are there still open points? Otherwise I'd like to close the bug.
>>
>>Best regards, Michael.
>
> As you added the documentation for it, please, close it then.

Done.

Best regards, Michael.