[R-pkg-devel] Reliably detecting FLIBS on source build of R (w.r.t Rust packages)

[Ivan Krylov]

В Sat, 25 Jan 2025 08:54:45 -0800
Balasubramanian Narasimhan <naras using stanford.edu> пишет:

> (https://github.com/blas-lapack-rs/r-src/blob/966266425b1a21a1e979f767c6023e6bf00616fc/build.rs#L160). 

Thank you for providing the link to the code!
 
> The only thing I can think of is that FLIBS is being set outside 
> config.site or Makevars during the R build.

I think this is happening because the r-src crate is running the wrong
R executable to determine the linker flags. The check system is running
/Users/ripley/R/R-devel/bin/R, while there's also a different R (for
example, /usr/local/bin/R) visible on the $PATH. The code ends up
getting the linker flags from the latter when it runs "R" [1].

I think it should be possible to sidestep this issue altogether if you
only enable the static library at [2] and then have R link the package
shared library for you from the static library produced by Rust using
the flags you're correctly setting in Makevars [3].

If you do need Rust to determine the linker flags by itself, make sure
to run ${R_HOME}/bin/R, not just R [4].

Unrelated but probably important: having 'all' or $(SHLIB) depend on a
target that removes the files you've built [5] is a bad idea because
Make is allowed to run independent recipes in undefined order,
including rm -Rf $(SHLIB) $(STATLIB) $(OBJECTS) while $(STATLIB) is
being built [6]. Note how 'rm -Rf ...' is the first command being run
in [7], before any compilation happens. The files you're removing as
part of the $(STATLIB) recipe should be enough; there shouldn't be any
need for the 'C_clean' recipe.

-- 
Best regards,
Ivan

[1]
https://github.com/blas-lapack-rs/r-src/blob/966266425b1a21a1e979f767c6023e6bf00616fc/build.rs#L112

[2]
https://github.com/oxfordcontrol/clarabel-r/blob/13219b94cfa018091cb3ea31c51dff2116704e0a/src/rust/Cargo.toml#L7
see also
https://github.com/r-rust/hellorust/blob/master/src/myrustlib/Cargo.toml

[3]
https://github.com/oxfordcontrol/clarabel-r/blob/13219b94cfa018091cb3ea31c51dff2116704e0a/src/Makevars.in#L12

[4]
https://cran.r-project.org/doc/manuals/R-exts.html#Configure-and-cleanup

[5]
https://github.com/oxfordcontrol/clarabel-r/blob/13219b94cfa018091cb3ea31c51dff2116704e0a/src/Makevars.in#L17

[6]
https://cran.r-project.org/doc/manuals/R-exts.html#Using-Makevars

[7]
https://www.stats.ox.ac.uk/pub/bdr/M1mac/clarabel.log