I noticed "./pre-inst-env guix build guix" fails on my computer due to
"pypi->guix-package, no wheel" failing.  Here is an excerpt from the log:

> test-name: pypi->guix-package, no wheel
> location: /tmp/guix-build-guix-1.3.0-24.2fb4304.drv-
> 0/source/tests/pypi.scm:221
> source:
> + (test-assert
> +   "pypi->guix-package, no wheel"
> +   (mock ((guix import utils)
> +          url-fetch
> +          (lambda (url file-name)
> +            (match url
> +                   ("https://example.com/foo-1.0.0.tar.gz"
> +                    (begin
> +                      (mkdir-p "foo-1.0.0/src/bizarre.egg-info")
> +                      (with-output-to-file
> +                        "foo-1.0.0/src/bizarre.egg-
> info/requires.txt"
> +                        (lambda () (display test-requires.txt)))
> +                      (parameterize
> +                        ((current-output-port (%make-void-port
> "rw+")))
> +                        (system* "tar" "czvf" file-name "foo-
> 1.0.0/"))
> +                      (delete-file-recursively "foo-1.0.0")
> +                      (set! test-source-hash
> +                        (call-with-input-file file-name port-
> sha256))))
> +                   (" 
> https://example.com/foo-1.0.0-py2.py3-none-any.whl"
> +                    #f)
> +                   (_ (error "Unexpected URL: " url)))))
> +         (mock ((guix http-client)
> +                http-fetch
> +                (lambda (url . rest)
> +                  (match url
> +                         ("https://pypi.org/pypi/foo/json"
> +                          (values
> +                            (open-input-string test-json-1)
> +                            (string-length test-json-1)))
> +                         (" 
> https://example.com/foo-1.0.0-py2.py3-none-any.whl"
> +                          #f)
> +                         (_ (error "Unexpected URL: " url)))))
> +               (match (pypi->guix-package "foo")
> +                      (('package
> +                        ('name "python-foo")
> +                        ('version "1.0.0")
> +                        ('source
> +                         ('origin
> +                          ('method 'url-fetch)
> +                          ('uri ('pypi-uri "foo" 'version))
> +                          ('sha256 ('base32 (? string? hash)))))
> +                        ('build-system 'python-build-system)
> +                        ('propagated-inputs
> +                         ('list 'python-bar 'python-foo))
> +                        ('native-inputs ('list 'python-pytest))
> +                        ('home-page "http://example.com")
> +                        ('synopsis "summary")
> +                        ('description "summary")
> +                        ('license 'license:lgpl2.0))
> +                       (and (string=?
> +                              (bytevector->nix-base32-string test-
> source-hash)
> +                              hash)
> +                            (equal?
> +                              (pypi->guix-package "foo" #:version
> "1.0.0")
> +                              (pypi->guix-package "foo"))
> +                            (guard (c ((error? c) #t))
> +                                   (pypi->guix-package
> +                                     "foo"
> +                                     #:version
> +                                     "42"))))
> +                      (x (pk 'fail x #f))))))
> actual-value: #f
> result: FAIL

Greetings,
Maxime.