dh_rust currently calls external Python-base wrapper script "cargo"
for all interaction with upstream tool "cargo"
that involves CARGO_HOME.

Better if CARGO_HOME functionality could be handled internally
in the D::D::Buildsystem::rust library,
simplifying code and avoiding dependency on python.

Possibly the wrapper does more than only handling CARGO_HOME.
Let's be cautious, and to begin with only internalize that part,
then see what is left to do to eliminate the wrapper.

 - Jonas
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Quoting Jonas Smedegaard (2024-07-16 13:47:15)

An interesting use case here is helvum:

Upstream build system is meson,
with CARGO_HOME=$BUILDDIR/cargo-home
which ideally should be possible to handle like this:

%:
        dh $@ --buildsystem meson+ninja --builddirectory build

execute_before_dh_auto_configure:
        dh_auto_configure --buildsystem rust --cargo-home build

 - Jonas

Quoting Jonas Smedegaard (2024-07-16 13:47:15)

An interesting use (and test) case here is rust-tonic:

Upstream includes with source some code in one subproject
which was generated by another subproject.

Debian source package should contain only source code,
so the source package is repackaged, stripping the generated files,
and during build the generating subproject is first run,
before build other parts.

Currently, calling the generating project is done
by setting up the required set of environment variables
and directly calling the Python wrapper.

I imagine that with internalized CARGO_HOME handling
done by dynamically adding/mangling settings in default CARGO_HOME,
then an unusual corner case is to test that rust-tonic still works.

 - Jonas