"documentation" traget requires breathe Python(3) package but does not test for it

[rhaas80]

After running meson in a build directory on my (Debian, bookworm, python-is-python2) workstation with sphinx installed via apt-get I was presented with:

[2/2] Generating sphinxdoc with a custom command
FAILED: docsrc/sphinx/index.html
/usr/bin/sphinx-build -b html -c /data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd/build/docsrc/sphinx /data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd/docsrc/sphinx /data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd/build/docsrc/sphinx
Running Sphinx v4.2.0

and the meson output was

ekohaes8: .../repos/RePrimAnd$ mkdir build
ekohaes8: .../repos/RePrimAnd$ cd build/
ekohaes8: .../RePrimAnd/build$ meson
The Meson build system
Version: 0.59.2
Source dir: /data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd
Build dir: /data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd/build
Build type: native build
Project name: RePrimAnd
Project version: 1.3
C compiler for the host machine: cc (gcc 10.3.0 "cc (Debian 10.3.0-11) 10.3.0")
C linker for the host machine: cc ld.bfd 2.37
C++ compiler for the host machine: c++ (gcc 10.3.0 "c++ (Debian 10.3.0-11) 10.3.0")
C++ linker for the host machine: c++ ld.bfd 2.37
Host machine cpu family: x86_64
Host machine cpu: x86_64
Found pkg-config: /usr/bin/pkg-config (0.29.2)
Run-time dependency Boost found: YES 1.74.0 (/usr/include)
Run-time dependency gsl found: YES 2.6
Run-time dependency HDF5 found: YES 1.10.7
Configuring test_config.h using configuration
Run-time dependency Boost (found: unit_test_framework) found: YES 1.74.0 (/usr)
Configuring bench_config.h using configuration
Program python found: YES (/usr/bin/python)
Program plot_benchmark.py found: YES (/data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd/tests/benchmarks/scripts/plot_benchmark.py)
Program plot_accuracy.py found: YES (/data/rhaas/postdoc/gr/cactus/ET_Next/repos/RePrimAnd/tests/benchmarks/scripts/plot_accuracy.py)
Configuring sroot_config.h using configuration
Program doxygen found: YES (/usr/bin/doxygen)
Configuring Doxyfile using configuration
Program sphinx-build found: YES (/usr/bin/sphinx-build)
Configuring conf.py using configuration
Program python3 (pybind11) found: NO
Program clang-tidy found: NO
Build targets in project: 20

Found ninja-1.10.1 at /usr/bin/ninja

after running apt-get install python3-breathe the command ninja documentation succeeded.

Since breathe is a dependency of documentation it should be tested for in the same manner sphinx is.