Subject: Re: [bug#60341] [PATCH Home] home: services: environment-variables: Add support for literal strings.

From: Andrew Tropin <[email-masked]>
Date: Tue, 27 Dec 2022 07:02:23 +0400

On 2022-12-26 19:19, Ludovic Courtès wrote:

> * gnu/home/services.scm (<literal-string>): New record type.
> (environment-variable-shell-definitions): Split 'shell-quote' into
> 'quote-string' and 'shell-double-quote'.  Add 'shell-single-quote'.
> Add clause for 'literal-string' records.
> * tests/guix-home.sh: Test it.
> * doc/guix.texi (Essential Home Services): Document it.
> ---
>  doc/guix.texi         | 14 ++++++++++---
>  gnu/home/services.scm | 48 ++++++++++++++++++++++++++++++++-----------
>  tests/guix-home.sh    |  4 +++-
>  3 files changed, 50 insertions(+), 16 deletions(-)
>
> Hi!
>
> I found that it’s occasionally useful to be able to define shell variables
> with a value that is to be taken literally, without shell expansion.  This
> is what this patch implements.
>
> Thoughts?

Hi Ludo,

the code looks good.

I'm a little conserned that one need to learn a new abstraction to
properly quote the expression instead of just using " or ' inside value
string, but we already have af4c103595a725194318f40fc5aba110772ff417 and
with the current state of the code this change looks rational and
idiomatic.  Also, it makes the interface more high-level, which can be
good in some circumstances.

>
> Ludo’.
>
> diff --git a/doc/guix.texi b/doc/guix.texi
> index efd281d9b0..44361b481a 100644
> --- a/doc/guix.texi
> +++ b/doc/guix.texi
> @@ -40972,13 +40972,15 @@ The easiest way to extend a service type, without defining a new service
>  type is to use the @code{simple-service} helper from @code{(gnu
>  services)}.
>  
> +@findex literal-string
>  @lisp
>  (simple-service 'some-useful-env-vars-service
>  		home-environment-variables-service-type
>  		`(("LESSHISTFILE" . "$XDG_CACHE_HOME/.lesshst")
>                    ("SHELL" . ,(file-append zsh "/bin/zsh"))
>                    ("USELESS_VAR" . #f)
> -                  ("_JAVA_AWT_WM_NONREPARENTING" . #t)))
> +                  ("_JAVA_AWT_WM_NONREPARENTING" . #t)
> +                  ("LITERAL_VALUE" . ,(literal-string "$@{abc@}"))))
>  @end lisp
>  
>  If you include such a service in you home environment definition, it
> @@ -40986,11 +40988,17 @@ will add the following content to the @file{setup-environment} script
>  (which is expected to be sourced by the login shell):
>  
>  @example
> -export LESSHISTFILE=$XDG_CACHE_HOME/.lesshst
> -export SHELL=/gnu/store/2hsg15n644f0glrcbkb1kqknmmqdar03-zsh-5.8/bin/zsh
> +export LESSHISTFILE="$XDG_CACHE_HOME/.lesshst"
> +export SHELL="/gnu/store/2hsg15n644f0glrcbkb1kqknmmqdar03-zsh-5.8/bin/zsh"
>  export _JAVA_AWT_WM_NONREPARENTING
> +export LITERAL_VALUE='$@{abc@}'
>  @end example
>  
> +Notice that @code{literal-string} above lets us declare that a value is
> +to be interpreted as a @dfn{literal string}, meaning that ``special
> +characters'' such as the dollar sign will not be interpreted by the
> +shell.
> +
>  @quotation Note
>  Make sure that module @code{(gnu packages shells)} is imported with
>  @code{use-modules} or any other way, this namespace contains the
> diff --git a/gnu/home/services.scm b/gnu/home/services.scm
> index 99035686f1..2c1f58fddf 100644
> --- a/gnu/home/services.scm
> +++ b/gnu/home/services.scm
> @@ -1,6 +1,7 @@
>  ;;; GNU Guix --- Functional package management for GNU
>  ;;; Copyright © 2021 Andrew Tropin <[email-masked]>
>  ;;; Copyright © 2021 Xinglu Chen <[email-masked]>
> +;;; Copyright © 2022 Ludovic Courtès <[email-masked]>
>  ;;;
>  ;;; This file is part of GNU Guix.
>  ;;;
> @@ -33,6 +34,7 @@ (define-module (gnu home services)
>    #:use-module (guix i18n)
>    #:use-module (guix modules)
>    #:use-module (srfi srfi-1)
> +  #:use-module (srfi srfi-9)
>    #:use-module (ice-9 match)
>    #:use-module (ice-9 vlist)
>  
> @@ -47,6 +49,10 @@ (define-module (gnu home services)
>              home-run-on-change-service-type
>              home-provenance-service-type
>  
> +            literal-string
> +            literal-string?
> +            literal-string-value
> +
>              environment-variable-shell-definitions
>              home-files-directory
>              xdg-configuration-files-directory
> @@ -171,32 +177,50 @@ (define home-profile-service-type
>  configuration files that the user has declared in their
>  @code{home-environment} record.")))
>  
> +;; Representation of a literal string.
> +(define-record-type <literal-string>
> +  (literal-string str)
> +  literal-string?
> +  (str literal-string-value))
> +
>  (define (environment-variable-shell-definitions variables)
>    "Return a gexp that evaluates to a list of POSIX shell statements defining
>  VARIABLES, a list of environment variable name/value pairs.  The returned code
>  ensures variable values are properly quoted."
> -  #~(let ((shell-quote
> -           (lambda (value)
> -             ;; Double-quote VALUE, leaving dollar sign as is.
> -             (let ((quoted (list->string
> -                            (string-fold-right
> +  #~(let* ((quote-string
> +            (lambda (value quoted-chars)
> +              (list->string (string-fold-right
>                               (lambda (chr lst)
> -                               (case chr
> -                                 ((#\" #\\)
> -                                  (append (list chr #\\) lst))
> -                                 (else (cons chr lst))))
> +                               (if (memq chr quoted-chars)
> +                                   (append (list chr #\\) lst)
> +                                   (cons chr lst)))
>                               '()
>                               value))))
> -               (string-append "\"" quoted "\"")))))
> +           (shell-double-quote
> +            (lambda (value)
> +              ;; Double-quote VALUE, leaving dollar sign as is.
> +              (string-append "\"" (quote-string value '(#\" #\\))
> +                             "\"")))
> +           (shell-single-quote
> +            (lambda (value)
> +              ;; Single-quote VALUE to enter a literal string.
> +              (string-append "'" (quote-string value '(#\' #\\))
> +                             "'"))))
>        (string-append
>         #$@(map (match-lambda
>                   ((key . #f)
>                    "")
>                   ((key . #t)
>                    #~(string-append "export " #$key "\n"))
> -                 ((key . value)
> +                 ((key . (? string? value))
>                    #~(string-append "export " #$key "="
> -                                   (shell-quote #$value) "\n")))
> +                                   (shell-double-quote #$value)
> +                                   "\n"))
> +                 ((key . (? literal-string? value))
> +                  #~(string-append "export " #$key "="
> +                                   (shell-single-quote
> +                                    #$(literal-string-value value))
> +                                   "\n")))
>                 variables))))
>  
>  (define (environment-variables->setup-environment-script vars)
> diff --git a/tests/guix-home.sh b/tests/guix-home.sh
> index d5e2dadbb5..423ebf6f33 100644
> --- a/tests/guix-home.sh
> +++ b/tests/guix-home.sh
> @@ -81,7 +81,8 @@ trap 'chmod -Rf +w "$test_directory"; rm -rf "$test_directory"' EXIT
>  
>     (simple-service 'add-environment-variable
>                     home-environment-variables-service-type
> -                   '(("TODAY" . "26 messidor")))
> +                   `(("TODAY" . "26 messidor")
> +                     ("LITERAL" . ,(literal-string "${abc}"))))
>  
>     (simple-service 'home-bash-service-extension-test
>                     home-bash-service-type
> @@ -149,6 +150,7 @@ EOF
>      grep -q "the content of ~/.config/test.conf" "${HOME}/.config/test.conf"
>      grep '^export PS1="\$GUIX_ENVIRONMENT λ "$' "${HOME}/.bash_profile"
>      ( . "${HOME}/.guix-home/setup-environment"; test "$TODAY" = "26 messidor" )
> +    ( . "${HOME}/.guix-home/setup-environment"; test "$LITERAL" = '${abc}' )
>  
>      # This one should still be here.
>      grep "stay around" "$HOME/.config/random-file"
>
> base-commit: 9369c1ccf47d9bf6f2e28a9454c1c329a2044f19

-- 
Best regards,
Andrew Tropin