Building from source using Meson

This is a short guide on how to build the Sage from source using Meson.

Walkthrough

Assume we’re starting from a clean repo and a fully set up conda environment (modify -linux according to your operating system):

$ mamba env create --file environment-3.11-linux.yml --name sage-dev
$ conda activate sage-dev

Alternatively, install all build requirements as described in section Prerequisites. In the likely case that you have to install some dependencies manually, set the correct environment variables to point to the installed libraries:

$ export C_INCLUDE_PATH=$C_INCLUDE_PATH:/your/path/to/include
$ export CPLUS_INCLUDE_PATH=$CPLUS_INCLUDE_PATH:/your/path/to/include
$ export LIBRARY_PATH=$LIBRARY_PATH:/your/path/to/lib

Note

If you have previously build Sage in-place, you first have to delete the already compiled files, e.g. with shopt -s globstar followed by rm src/**/*.so or for f in src/**/*.so ; do mv "$f" "$f.old"; done. Moreover, remove the old generated files with find src/sage/ext/interpreters -type f ! -name 'meson.build' -delete. Also uninstall the ‘old’ sage packages with pip uninstall sage-conf sage-setup sagemath-standard.

To compile and install the project in editable install, just use:

$ pip install --no-build-isolation --editable .

This will install Sage in the current Python environment. In a Conda environment, the --no-build-isolation flag is necessary to allow the build system to reuse the already installed build dependencies. If you don’t use Conda, you can omit this flag.

You can then start Sage from the command line with ./sage or run the tests with ./sage -t.

Note

By using pip install --editable in the above steps, the Sage library is installed in editable mode. This means that when you only edit source files, there is no need to rebuild the library; it suffices to restart Sage. Note that this even works when you edit Cython files (they will be recompiled automatically), so you no longer need to manually compile after editing Cython files.

Note

Note that make is not used at all, nor is configure. This means that any Sage-the-distribution commands such as sage -i will not work.

Note

By default, Meson will automatically determine the number of jobs to run in parallel based on the number of CPU available. This can be adjusted by passing --config-settings=compile-args=-jN to pip install.

--verbose can be passed to pip install, then the meson commands internally used by pip will be printed out.

Background information

Under the hood, pip invokes meson to configure and build the project. We can also use meson directly as follows.

To configure the project, we need to run the following command:

$ meson setup builddir --prefix=$PWD/build-install

This will create a build directory builddir that will hold the build artifacts. The --prefix option specifies the directory where the Sage will be installed.

If pip is used as above, builddir is set to be build/cp[Python major version][Python minor version], such as build/cp311. --prefix= can be left unspecified, when conda is used then meson will install to the conda environment e.g. $HOME/miniforge3/envs/sage-dev/.

To compile the project, run the following command:

$ meson compile -C builddir

Installing is done with the following command:

$ meson install -C builddir

This will then install in the directory specified by --prefix, e.g. build-install/lib/python3.11/site-packages/sage. Usually, this directory is not on your Python path, so you have to use:

$ PYTHONPATH=build-install/lib/python3.11/site-packages ./sage

When editable install is used, it is not necessary to reinstall after each compilation.

Alternatively, we can still use pip to install:

$ pip install --no-build-isolation --config-settings=builddir=builddir --editable .

Tip

Package maintainers may want to specify further build options or need to install to a different directory than the install prefix. Both are supported naturally by Meson:

$ meson setup builddir --prefix=/usr --libdir=... -Dcpp_args=...
$ meson compile -C builddir
$ DESTDIR=/path/to/staging/root meson install -C builddir

See Meson’s quick guide and Meson’s install guide for more information.

Miscellaneous tips

The environment variable MESONPY_EDITABLE_VERBOSE=1 can be set while running ./sage, so that when Cython files are recompiled a message is printed out.

If a new .pyx file is added, it need to be added to meson.build file in the containing directory.

Unlike the make-based build system which relies on header comments # distutils: language = c++ to determine whether C++ should be used, Meson-based build system requires specifying override_options: ['cython_language=cpp'] in the meson.build file. Similarly, dependencies need to be specified by dependencies: [...].