Memoizing macro values

[Miro Hrončok]

On 02. 01. 23 10:13, Panu Matilainen wrote:
> On 12/21/22 12:17, Florian Weimer wrote:
>> In Fedora, we have this:
>>
>> /usr/lib/rpm/macros.d/macros.python:%python_sitelib %(RPM_BUILD_ROOT= 
>> %{__python} -Esc "import sysconfig; print(sysconfig.get_path('purelib', 
>> vars={'platbase': '%{_prefix}', 'base': '%{_prefix}'}))")
>> /usr/lib/rpm/macros.d/macros.python3:%python3_sitelib %(RPM_BUILD_ROOT= 
>> %{__python3} -Ic "import sysconfig; print(sysconfig.get_path('purelib', 
>> vars={'platbase': '%{_prefix}', 'base': '%{_prefix}'}))")
>>
>> This is a %define-style macro, so the macro gets re-evaluated for every
>> expansion.  It can make spec file operations really, really slow.
>>
>> It's possible to work around this in spec files like this:
>>
>> %{?python3_sitearch: %global python3_sitearch %{python3_sitearch}}
>>
>> But this is quite ugly, and I wonder if there is a nice way to do it
>> directly in the macros file instead.  I think I know how do it with Lua,
>> but maybe there is a better way?
> 
> %python3_sitearch %{global python3_sitearch %(RPM_BUILD_ROOT= %{__python3} -Esc 
> "import sysconfig; print(sysconfig.get_path('platlib', vars={'platbase': 
> '%{_prefix}', 'base': '%{_prefix}'}))")}%{python3_sitearch}
> 
> Ie just push the evaluated macro on top of the original one as a global on 
> first use, re-evaluation can be forced with %undefine and no helper macros needed.

How does this work when Python is installed mid-build somehow? Do we need to 
care about that or can we absolutely assume that when packages are installed, 
the RPM build process is restarted?

> There's also an upstream RFE on this use-case, it's quite common indeed: 
> https://github.com/rpm-software-management/rpm/issues/1155

Thanks for the link.

-- 
Miro Hrončok
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