Improve flint subproject

[tobiasdiez]

Currently, we have to have a bunch of header files as patch in the flint subproject since we want to have imports of the type #include <flint/acb_calc.h> working but acb_calc.h is not in a flint folder.

See #40071 (comment) for more details.

[dimpase]

Is this because you don't call a flint's build system?

[nbruin]

On my Fedora box I find:

/usr/include/flint/acb_calc.h

so it looks like when flint is installed, this header file does end up in a very standard-looking place. Shouldn't you just let flint install itself and then use the header file from the installation location? I guess this is the scenario where sage installs "flint" by itself, but even then we should give flint an opportunity to install itself, right? And then whatever code we need flint in should only try to build once that installation has completed.

[dimpase]

I believe it is not a big problem for meson to use flint's build system - via https://mesonbuild.com/External-Project-module.html

However, meson docs are rather brief and unclear on this. They say that the default method to build a subproject is meson, but there is no meson.build for flint anywhere here, it seems, and flint itself doesn't have a meson.build available.

Thus it seems it builds flint using flint's makefiles, but somehow it doesn't quite work without this extra patch. (Or perhaps I am wrong, and it ignores all the fine tuning provided by flint's autotools build, and does some kind of default meson thing, which is rather opaque - at least to me)

[tobiasdiez]

On my Fedora box I find:

/usr/include/flint/acb_calc.h

so it looks like when flint is installed, this header file does end up in a very standard-looking place. Shouldn't you just let flint install itself and then use the header file from the installation location? I guess this is the scenario where sage installs "flint" by itself, but even then we should give flint an opportunity to install itself, right? And then whatever code we need flint in should only try to build once that installation has completed.

Right, flints autoconf/make build copies the headers after the build to the 'correct' place.

But when building flint as a meson subproject, it is not really installed before sagelib is compiled - all the compilation of subprojects and the main library happens at the same time.

meson to use flint's build system - via https://mesonbuild.com/External-Project-module.html

Yes, the flint subproject currently makes sense of this autoconf integration.

[dimpase]

Sorry, I don't understand - does flint subproject currently use ExternalProject facility?

a subproject is not ready to be consumed until it's installed, so it's a meson bug if it delays the installation to some last moment.

[nbruin]

A brief look at flint, and particularly flintlib/flint#1910, gives me the impression that meson build support for flint is immature. It's promising that meson for flint is being worked on, but perhaps it's a bit early days to let sage depend on it? It should be possible in meson to specify that certain prerequisites should be built via autoconf etc., right? Perhaps stick with that until the Flint people themselves say it's ready for production use? From what I could see, using cmake or meson for flint was advised against outside Windows.