Re: [PATCH] org.el: Fix percent substitutions in `org-open-file'

[Max Nikulin <manikulin@gmail.com>]

On 02/09/2022 19:08, Ihor Radchenko wrote:
> Max Nikulin writes:
> 
>> Subject: [PATCH] org.el: Fix percent substitutions in `org-open-file'
> 
>> +(defun org--open-file-format-command
>> +    (mailcap-command file link match-data)
>> +  "Format MAILCAP-COMMAND to launch viewer for FILE.
>> +
>> ...
>> +For example, to specify particular location withing a PDF file,
>> +`org-file-apps' list may have the following entries (order is important):
>> +
>> +    ;; Page and search string,
>> +    ;; e.g. <file:///usr/share/doc/bash/bashref.pdf::34::order of redirections>.
>> +    (\"\\\\.pdf::\\\\([0-9]+\\\\)::\\\\(.+\\\\)\\\\\\='\"
>> +        . \"okular --page %1 --find %2 %s\")
>> +    ;; Internal anchor and search string,
>> +    ;; e.g. <file:///usr/share/doc/bash/bashref.pdf::Redirections::allocate a file>.

In the meanwhile I have realized that it should be

<file:///usr/share/doc/bash/bashref.pdf::#Redirections::allocate a file>

To allow just search as

<file:///usr/share/doc/bash/bashref.pdf::allocate a file>

>> +    (\"\\\\.pdf::\\\\(.+\\\\)::\\\\(.+\\\\)\\\\\\='\"
>> +        . \"okular --find %2 file://%s\\\\\\\\#%1\")
>> +    ;; Page number, e.g. <file:///usr/share/doc/bash/bashref.pdf::34>.
>> +    (\"\\\\.pdf::\\\\([0-9]+\\\\)\\\\\\='\" . \"okular --page %1 %s\")
>> +    ;; Internal reference, e.g. <file:///usr/share/doc/bash/bashref.pdf::Redirections>.

And <file:///usr/share/doc/bash/bashref.pdf::#Redirections>
As a side effect it should dramatically reduce number of backslashes 
since hash symbol becomes a part of %1 substitution.

>> +    (\"\\\\.pdf::\\\\(.+\\\\)\\\\\\='\" . \"okular file://%s\\\\\\\\#%1\")
>> +    ;; No location within the file, optionally followed by \"::\",
>> +    ;; e.g. <file:///usr/share/doc/bash/bashref.pdf>.
>> +    (\"\\\\.pdf\\\\(?:::\\\\)?\\\\\\='\" . \"okular %s\")
> 
> This is a nice set of examples, but it probably does not belong to this
> docstring. I'd rather see this in `org-file-apps' docstring or even in
> the manual.

I thought on this and I do not think it should be added to the manual. 
Instead a set of hooks should be defined for popular PDF viewers: 
evince, zathura, xpdf, firefox, chromium & Co, etc. Such hook injects a 
number of supported `org-file-apps' records and users may add suitable 
hook to e.g. (with-eval-after-load 'org (push ...)). It may be 
implemented as a dedicated package org-pdf-viewers.el. The only problems 
is that adding entries programmatically breaks easy customization 
interface for `org-file-apps'. Currently there is the same issue with 
`org-link-parameters' that is a defcustom variables with entries added 
by various org extensions.

I added the example with hope to better explain the purpose of this 
function.