GNU bug report logs - #76007
31.0.50; Interpreter not correctly found when using nix-shell.

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Message #15 received at 76007-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Malcolm Purvis <malcolm <at> purvis.id.au>
Cc: 76007-done <at> debbugs.gnu.org
Subject: Re: bug#76007: 31.0.50;
 Interpreter not correctly found when using nix-shell.
Date: Sat, 1 Mar 2025 19:35:58 -0800

Stefan Kangas <stefankangas <at> gmail.com> writes:

> Malcolm Purvis <malcolm <at> purvis.id.au> writes:
>
>> In NixOS if you want to use a script that manages its own
>> dependencies, you use a command called "nix-shell" or "nix shell"
>> to launch the script.
>>
>> The start of such a script looks like:
>>
>> #! /usr/bin/env nix-shell
>> #! nix-shell -i bash -p imagemagick cowsay
>>
>> or
>>
>> #! /usr/bin/env nix
>> #! nix shell github:tomberek/-#perlWith.HTMLTokeParserSimple.LWP
>>    --command perl -x
>>
>> The OS interpreter is nix-shell and nix-shell launches the real
>> interpreter to execute the rest of the script.
>>
>> With these scripts, Emacs's current behaviour is as follows:
>>
>> - nix-shell is not interpreter-mode-alist so Emacs looks at the
>>   file's
>>  extension:
>>
>>  - If the file has an extension then the correct mode is used
>>  - If the file does not have an extension then Fundamental mode is
>>  used
>>    regardless of the script's actual language.
>>
>> If the file is a shell script with the correct extension, sh-mode
>> is used but sh-mode fails to guess the shell, leaving the variable
>> sh-shell as 'nix-shell.
>>
>> In most cases this means that some shell features are not enabled,
>> but otherwise it is possible to edit the script.
>>
>> However, lsp-mode's bash language support (lsp-bash.el) throws an
>> error if sh-shell is not set to it's supported values ('sh and
>> 'bash), and as a result nix bash scripts fail.
>>
>> The solution is to add a new regexp to
>> auto-mode-interpreter-regexp that will detect a nix script and
>> extract the real interpreter from the second line.  Nix shell can
>> be invoked in a number of ways but this regexp matches the common
>> forms.
>>
>>
>> diff --git a/lisp/files.el b/lisp/files.el
>> index 5ff40c335d7..1f3ac1431d2 100644
>> --- a/lisp/files.el
>> +++ b/lisp/files.el
>> @@ -3389,6 +3389,7 @@ and `inhibit-local-variables-suffixes'.  If
>>     "\\(?:[^ \t\n]+=[^ \t\n]*[ \t]+\\)*"
>>     "\\)?"
>>     "\\)?"
>> +   "\\(?:\\(?:nix\\|nix-shell\\)\n#![
>> \t]+\\(?:nix\\|nix-shell\\).*\\(?:-i\\|--command\\)[ \t]+\\)?"
>>     ;; Group 2: interpreter.  "\\([^ \t\n]+\\)")
>>    "Regexp matching interpreters, for file mode determination.
>>
>>
>> Malcolm
>
> Thanks for the bug report.
>
> This looks to me like a bug in lsp-mode, or lsp-bash.el.  I recommend
> reporting the bug to them first.

No further comments within 4 weeks, so I'm closing this bug.

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