bug#48331: [PATCH draft] build-system: emacs: Generate -pkg.el file in case it is missing

[Leo Prikler <leo.prikler@student.tugraz.at>]

Am Dienstag, den 25.05.2021, 16:40 +0300 schrieb Andrew Tropin:
> ---
> Thank you for the patches, tested, works for me!  The solution is
> much more precise than mutating package-directory-list variable, good
> job.  I don't see any major problems in the implementation (but I'm
> not very fluent elisp dev and maybe missing something).
Don't worry, I can wait for a proper review by some of our experts,
since we shouldn't mess with emacs-build-system all too often anyway :P

> I drafted a simple build phase, which generates -pkg.el in case it is
> missing.
> 
> There are at least a few problems with this implementation:
> 
> 1. There is no information about package record available during
> build, which makes it hard to get package name and package
> version.  I can't use any regexp to obtain this information from name
> or elpa-name-ver, because  package name and version can have
> arbitrary form: comment-dwim-2-1.0, cyberpunk-2019-theme-20191008-
> alpha or something like that.
> 2. It's also not so easy to extract description of the package from
> somewhere, the first option is to pass package record to build phases
> somehow, another is to parse PACKAGE-NAME.el file comments section.
> 3. This one I consider as a minor flaw: there is no generic solution
> for packages built with build systems other than emacs-build-system.
3. is easy -- just have those packages call the phase through emacs-
build-system.  There already exist packages which do that, and it
should be pretty straightforward to do.

For 1. and 2. I think you're thinking a little too complicated.  We can
call Emacs at build time.  In particular, we can use all of the lisp-
mnt stuff, that I used in emacs-dpd at build time, we just need to
write the (define-package ...) form to disk.
In order to pick the right file, we can either use package-name (see
discussion below) or the name of the pkg-file without -pkg.  Come to
think about it, we might also provide #:pkg-file-name as a keyword and
only generate the package file if it's set to a value other than #f,
i.e. let the packager choose whether they want to generate a -pkg.el
file.  Something along this line is done with the build.xml of ant-
build-system.

>  So, this patch is very dirty and I publish it only for future
> reference.
> 
> The intuition says that we should split name and version in build
> phase arguments, also it seems that it will be useful to provide
> other information about package during build time for cases like this
> one.  I'll learn this area a bit more and probably will make another
> thread someday.
IIRC, there's a demand for having package-name and package-version
available during build (which might get through next core-updates or
might not -- we'll see), but I don't think we can argue for
description, especially when the Guix description might not be the
thing package.el wants here.

>  guix/build/emacs-build-system.scm | 60
> ++++++++++++++++++++++++++++++-
>  1 file changed, 59 insertions(+), 1 deletion(-)
> 
> diff --git a/guix/build/emacs-build-system.scm
> b/guix/build/emacs-build-system.scm
> index f13162d6c4..2bb102b4be 100644
> --- a/guix/build/emacs-build-system.scm
> +++ b/guix/build/emacs-build-system.scm
> @@ -116,6 +116,63 @@ environment variable\n" source-directory))
>      (parameterize ((%emacs emacs))
>        (emacs-byte-compile-directory (elpa-directory out)))))
> 
> +
> +(define* (add-pkg-file-if-missing #:key name outputs #:allow-other-
> keys
> +                                  #:rest args)
> +  "Generate simple -pkg.el in case package doesn't have it in source
> code."
> +  (define (file-contains-nul-char? file)
> +    (call-with-input-file file
> +      (lambda (in)
> +        (let loop ((line (read-line in 'concat)))
> +          (cond
> +           ((eof-object? line) #f)
> +           ((string-index line #\nul) #t)
> +           (else (loop (read-line in 'concat))))))
> +      #:binary #t))
> +
> +  (let* ((out (assoc-ref outputs "out"))
> +         (el-dir (elpa-directory out))
> +         (elpa-name-ver (store-directory->elpa-name-version out))
> +         (el-files (remove file-contains-nul-char?
> +                           (find-files (getcwd) "\\.el$")))
> +         (el-names (map (lambda (x) (basename x ".el")) el-files))
> +
> +         (possible-names
> +          (fold (lambda (x acc)
> +                  (cons
> +                   (string-append
> +                    (if (not (null? acc)) (string-append (first acc)
> "-") "")
> +                    x)
> +                   acc))
> +                '()
> +                (string-split elpa-name-ver #\-)))
> +
> +         (package-names (append-map
> +                         (lambda (name)
> +                           (let ((m (member name el-names)))
> +                             (if m (list (car m)) '())))
> +                         possible-names))
> +
> +         (package-name (if (null? package-names) "" (car package-
> names)))
> +         (package-version (string-drop elpa-name-ver
> +                                       (1+ (string-length package-
> name))))
> +         (package-description "description should be here")
> +         (pkg-file (string-append el-dir "/" package-name "-
> pkg.el")))
> +
> +    (when (not (file-exists? pkg-file))
> +      (with-output-to-file pkg-file
> +        (lambda ()
> +          (format
> +           #t
> +           "\
> +(define-package
> +  ~s
> +  ~s
> +  ~s
> +  nil)"
> +           package-name package-version package-description))))
> +    #t))
> +
>  (define* (patch-el-files #:key outputs #:allow-other-keys)
>    "Substitute the absolute \"/bin/\" directory with the right
> location in the
>  store in '.el' files."
> @@ -293,8 +350,9 @@ for libraries following the ELPA convention."
>      (add-after 'make-autoloads 'enable-autoloads-compilation
>        enable-autoloads-compilation)
>      (add-after 'enable-autoloads-compilation 'patch-el-files patch-
> el-files)
> +    (add-after 'patch-el-files 'add-pkg-file-if-missing
> add-pkg-file-if-missing)
>      ;; The .el files are byte compiled directly in the store.
> -    (add-after 'patch-el-files 'build build)
> +    (add-after 'add-pkg-file-if-missing 'build build)
>      (add-after 'build 'validate-compiled-autoloads validate-
> compiled-autoloads)
>      (add-after 'validate-compiled-autoloads 'move-doc move-doc)))
>