import: cpan: Fix license string for Artistic license.

* guix/import/cpan.scm (string->license): Remove extraneous "_0"
  suffix for Artistics licenses.

Merge branch 'master' into core-updates

import: Add hackage importer.

* guix/import/hackage.scm: New file.
* tests/hackage.scm: New file.

Merge branch 'master' into core-updates

import: cpan: Change %corelist into a promise.

Fixes compilation failures in 'guix pull'.

* guix/import/cpan.scm (%corelist): Change it to a promise by wrapping it with
  'delay'.
  (cpan-module->sexp): Adapt uses of %corelist by wrapping with 'force'.

import: cpan: Use cpan mirror url.

* guix/import/cpan.scm (cpan-module->sexp)[source-url]: Substitute cpan mirror
  url.

import: cpan: Sort inputs.

* guix/import/cpan.scm (cpan-module->sexp)[convert-inputs]: Sort returned list
  of inputs.

import: cpan: Adjust licenses.

* guix/import/cpan.scm (string->license): Add artistic2.0.  Use
  '(package-license perl) for "perl_5" as is our convention.

import: cpan: Use corelist to filter dependencies.

* guix/import/cpan.scm (%corelist): New variable.
  (module->dist-name, core-module?): New procedures.
  (cpan-module->sexp)[convert-inputs]: Use them.  Include "test" dependencies
  in converted inputs.
* doc/guix.texi (Invoking guix import)[cpan]: Mention corelist filtering.

Merge branch 'master' into core-updates

import: Add CPAN importer.

* guix/import/cpan.scm, guix/scripts/import/cpan.scm, tests/cpan.scm:
  New files.
* Makefile.am (MODULE)[HAVE_GUILE_JSON]: Add them.
* guix/scripts/import.scm (importers): Add cpan.
* doc/guix.texi (Requirements): Mention `guix import cpan` as a user
  of guile-json.
  (Invoking guix import): Document new `guix import cpan` command.

import: Factorize utility functions.

* guix/import/pypi.scm (hash-table->alist, flatten, assoc-ref*,
  url-fetch, json-fetch): Pull procedures from here into...
* guix/import/utils.scm: Here and...
* guix/import/json.scm: Here.  New file.
* Makefile.am (MODULE)[HAVE_GUILE_JSON]: Add it.
* guix/import/gnu.scm (file-sha256): Move from here to...
* guix/hash.scm: Here.
* tests/pypi.scm (pypi->guix-package): Update mock module reference.

import: gnu: Propagate the key-download argument.

* guix/import/gnu.scm (gnu->guix-package): Pass the key-download
  argument on to gnu-package->sexp.

Merge branch 'master' into 'core-updates'.

import: gnu: Write the hash in nix-base32 format.

* guix/import/gnu.scm (gnu-package->sexp): Use
  'bytevector->nix-base32-string', not 'bytevector->base32-string'.

import: Add GNU importer.

Suggested by Karl Berry <karl@gnu.org>
and Andreas Enge <andreas@enge.fr>.

* guix/import/gnu.scm, guix/scripts/import/gnu.scm: New files.
* Makefile.am (MODULES): Add them.
* guix/scripts/import.scm (importers): Add "gnu".
* guix/gnu-maintenance.scm (gnu-release-archive-types): New procedure.
  (download-tarball): Export.

import: pypi: Gracefully handle non-existent packages.

Fixes <http://bugs.gnu.org/18831>.
Reported by Ian Denhardt <ian@zenhack.net>.

* guix/import/pypi.scm (url-fetch, json-fetch, pypi-fetch): Augment
  docstring to mention #f on failure.
  (pypi->guix-package): Likewise, and actually return #f on failure.
* guix/scripts/import/pypi.scm (guix-import-pypi): Call 'leave' when
  'pypi->guix-package' returns #f.

import: snix: Handle license attributes.

* guix/import/snix.scm (snix-derivation->guix-package)[license-variable]:
  Move to...
  (license-variable): ... here.  Handle license attributes.

guix import pypi: Fix a typo in a docstring.

* guix/import/pypi.scm (snake-case): Fix documentation.

guix import pypi: do not add "python-" to a package name if it's already there.

* guix/import/pypi.scm (make-pypi-sexp): test whether the package name starts
  with "python-" before modifying it.