* guix/discovery.scm, tests/discovery.scm: New files. * gnu/packages.scm (scheme-files, file-name->module-name) (scheme-modules, all-package-modules): Remove. (fold-packages): Rewrite in terms of 'fold-module-public-variables'. * gnu/tests.scm: Use (guix discovery). * Makefile.am (MODULES): Add guix/discovery.scm. (SCM_TESTS): Add tests/discovery.scm.