Understanding of the Declarative builds, Python edition

[hroncok]

Hello. I've just located #1087 in https://fedoraproject.org/wiki/Changes/RPM-4.20 and I've read https://rpm-software-management.github.io/rpm/manual/buildsystem.html

I am trying to understand how to use this, so let's dive in.

Suppose I currently have this specfile simplified from https://docs.fedoraproject.org/en-US/packaging-guidelines/Python/#_example_spec_file

Name:                 python-pello
Version:              1.0.4
Release:              1%{?dist}
Summary:              Example Python library

License:              MIT-0
URL:                  https://github.com/fedora-python/Pello
Source:               %{url}/archive/v%{version}/Pello-%{version}.tar.gz

BuildArch:            noarch

%description
...

%package -n python3-pello
Summary:              %{summary}
Recommends:           python3-pello+color

%description -n python3-pello
...


%pyproject_extras_subpkg -n python3-pello color

%prep
%autosetup -p1 -n Pello-%{version}


%generate_buildrequires
%pyproject_buildrequires -t


%build
%pyproject_wheel


%install
%pyproject_install
%pyproject_save_files -l pello


%check
%pyproject_check_import
%tox


%files -n python3-pello -f %{pyproject_files}
%doc README.md
%{_bindir}/pello_greeting


%changelog

---

If I defined the following macros (in any macro file?):

%buildsystem_pyproject_generate_buildrequires(rRxtNwe:C:) %pyproject_buildrequires %**
%buildsystem_pyproject_build(C:) %pyproject_wheel %**
%buildsystem_pyproject_install(l) %pyproject_install %["%**" == "" ? "" : "\
%pyproject_save_files %**"]
%buildsystem_pyproject_check(e:t) %pyproject_check_import %**

The spec could be simplified as such:

Name:                 python-pello
Version:              1.0.4
Release:              1%{?dist}
Summary:              Example Python library

License:              MIT-0
URL:                  https://github.com/fedora-python/Pello
Source:               %{url}/archive/v%{version}/Pello-%{version}.tar.gz

BuildArch:            noarch

BuildSystem:          pyproject
BuildOption(prep):    -n Pello-%{version}
BuildOption(generate_buildrequires): -t
BuildOption(install): -l pello

%description
...

%package -n python3-pello
Summary:              %{summary}
Recommends:           python3-pello+color

%description -n python3-pello
...

%pyproject_extras_subpkg -n python3-pello color


%check -a
%tox


%files -n python3-pello -f %{pyproject_files}
%doc README.md
%{_bindir}/pello_greeting


%changelog

Is that assumption correct?

(And as a side question, with #2859 we would not even need to set BuildOption(prep), right?)

[pmatilai]

That's the essence of it, yes.

There might be something else in the details I missed, but one thing that did catch my eye:
the %buildsystem_foo_install() and such macros do not take options currently because they'd be shared across all buildsystems. So eg %buildsystem_pyproject_check(e:t) will not do what you intend, there's no way to pass options to the buildsystem macro itself. What you pass to BuildOption(): will get passed as an argument (ie after --) to this macro, which you just pass along to the thing actually implementing it - such as %pyproject_* here.

As for #2859, the new -C flag is not automatically enabled anywhere just now, it probably should be in %buildsystem_default_prep() though, that's a good point.

[hroncok]

As long as it won't tell me Unknown option l in buildsystem_pyproject_install but let me pass any option further down via %**, good (even better, so I won't have to duplicate the option list).

[hroncok]

Should I open an issue for -C to be the default for BuildOption(prep)?

[pmatilai]

That would be good so it wont go forgotten, yeah.

[hroncok]

#2998

[pmatilai]

On that note, don't hesitate to point out shortcomings or other new related ideas. I'm too close to the source (in both meanings 😄 ) to see clearly, as the -C example points out.

[pmatilai]

FWIW, I revived my rpm-snapshot repository where you can get Fedora compatible builds from rpm so if folks want to try this out before the soon-to-be-released 4.20 alpha, there goes: git: https://copr.fedorainfracloud.org/coprs/pmatilai/rpm-snapshot/

[pmatilai]

FWIW, turns out this stuff is pretty crippled in the alpha release due to these two issues:
#3024
#2204

They don't prevent one from developing buildsystems but pretty much prevent using them in real-world packages where local tweaks are needed 😞