Subject: bug#76007: closed (Re: bug#76007: 31.0.50; Interpreter not correctly found when using nix-shell.)

From: [email-masked] (GNU bug Tracking System)
Date: Sun, 02 Mar 2025 03:37:02 +0000

Your bug report

#76007: 31.0.50; Interpreter not correctly found when using nix-shell.

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
76007: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=76007
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#76007: 31.0.50; Interpreter not correctly found when using nix-shell.
From: Stefan Kangas <[email-masked]>
To: Malcolm Purvis <[email-masked]>
Cc: [email-masked]
Date: Sat, 1 Mar 2025 19:35:58 -0800
List-Id: <debbugs-submit.debbugs.gnu.org>

Stefan Kangas <[email-masked]> writes:

> Malcolm Purvis <[email-masked]> 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.

Subject: 31.0.50; Interpreter not correctly found when using nix-shell.
From: Malcolm Purvis <[email-masked]>
To: [email-masked]
Date: Sun, 02 Feb 2025 22:46:44 +1100
List-Id: <debbugs-submit.debbugs.gnu.org>

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

In GNU Emacs 31.0.50 (build 2, x86_64-apple-darwin24.2.0, NS
appkit-2575.30 Version 15.2 (Build 24C101)) of 2025-01-11 built on
lamechWindowing system distributor 'Apple', version 10.3.2575
System Description:  macOS 15.2
 
Configured using:
 'configure 
 --enable-locallisppath=/usr/local/share/emacs/site-lisp 
 --infodir=/usr/local/Cellar/emacs-head@31/31.0.50_1/share/info/emacs 
 --prefix=/usr/local/Cellar/emacs-head@31/31.0.50_1 --without-x 
 --without-dbus --with-native-compilation --with-imagemagick 
 --with-modules --with-gnutls --with-rsvg --with-xml2 
 --with-xwidgets --with-webp --with-ns --disable-ns-self-contained 
 'CFLAGS=-O2 -march=native -pipe -DFD_SETSIZE=10000 
 -DDARWIN_UNLIMITED_SELECT' 'LDFLAGS=-L/usr/local/lib/gcc/14 
 -I/usr/local/opt/gcc/include -I/usr/local/opt/libgccjit/include 
 -I/usr/local/opt/gmp/include -I/usr/local/opt/jpeg/include''

-- 
		    Malcolm Purvis <[email-masked]>