On 12/17/20 11:05 AM, Ben Cotton wrote:

https://fedoraproject.org/wiki/Changes/Enable_Spec_File_Preprocessing


== Summary ==
This change should enable an opt-in spec file preprocessor in Fedora
infrastructure for the benefit of packagers. The preprocessor allows
some very neat tricks that were impossible before, for example
generate changelog and release automatically from git metadata or pack
the entire dist-git repository into an rpm-source tarball (effectively
allowing unpacked repos to live in DistGit).

== Owner ==
* Name: [[User:clime| Michal Novotný]]
* Email: clime@fedoraproject.org


== Detailed Description ==

There is a recently added feature into mock:
[https://github.com/rpm-software-management/mock/wiki/Plugin-rpkg-preprocessor
the rpkg preprocessor] which, if enabled, introduces an intermediate
step just before srpm building. This step consists of running the spec
file through a text preprocessing engine that includes an already
present library of macros designed specifically for rpm spec file
generation from git metadata. This library is called
[https://docs.pagure.org/rpkg-util/v3/macro_reference.html
rpkg-macros]. The macros there allow packagers to have their
`%changelog`, `Release`, `Version`, `VCS` tag, or even `Source` fields
automatically generated from dist-git repository data and metadata.
The library can be easily extended in future to support more packager
use-cases or even a completely new library can be developed that
doesn't look at git metadata at all and instead, for example, analyses
already present tarball content to render spec file based on upstream
information. This doesn't mean it will happen but the framework is
generic enough to support that. There is also support for user-defined
macros that are loaded on-demand from a file placed alongside the
package sources, maintained by packager. This feature wouldn't be
enabled by this change from start but it's an example of freedom that
the preprocessing framework is able to provide. Enabling this change
should be very easy, basically adding:

<pre>
config_opts['plugin_conf']['rpkg_preprocessor_enable'] = True
</pre>

into mock configuration of Koji builders and using at least mock 2.7.
Some very minor change may be also needed in Koji regarding the spec
file lookup.

Even if the change is enabled on the infrastructure level like this,
the packager will still need to opt-in to use the preprocessor. The
opting-in is done by placing `rpkg.conf` file into the package
top-level directory with the following content:

<pre>
[rpkg]
preprocess_spec = True
</pre>

When this is done by a packager, the preprocessor will be finally
enabled for the given package.

Alongside, there is an ongoing work to add the preprocessor support
into the `rpkg` python library so that a packager can easily work with
the spec files containing the preprocessor (rpkg) macros:
https://pagure.io/rpkg/pull-request/530

Is this pull request needed so that the preprocessor will run if I do `fedpkg mockbuild` or does fedpkg already do this if the preprocessor is enabled?

-Tom

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