Rust 1.15 and its shared libraries - Rust - Fedora mailing-lists

2 Feb 2017


      Rust 1.15 was released today, yay!  I'm working on the update, but
wanted to run something by you folks.
First, thanks to the Rust ABI or lack thereof, I've made efforts to
strongly discourage the use of "dylib" targets and linking, to the point
that I currently have removed *.so from rustlib/ entirely, and the
remaining libraries in %{_libdir} have their .rustc metadata stripped.
Without the metadata, you can't link to them at all, so they're only
useful to rustc itself.  Finally, the rust.spec has requires/provides
filtering to exclude all Rust libraries.
However, the big new feature of 1.15 is proc_macro, aka custom derive,
aka macros 1.1.  These are basically compiler plugins, and must be
compiled as a shared library for the build system (not the target).  But
that also means it's linking user code to dynamic versions of Rust
libraries, so it needs the libraries to be in rustlib/$build_target/lib
with the .rustc metadata that I've been stripping.
So, I need to restore that (or rather leave it alone), yet I still would
insist that no other code should ship linked to dynamic libraries.  The
ABI is not a problem for custom derive because these are transient
during a build, not something we'll package up.
Another thing to note is that the libraries that Rust installs in
%{_libdir} are identical to those under rustlib/$target/lib/.
So my tentative plan is:
- Stop stripping .rustc from the libraries.
  - Also have to set _find_debuginfo_opts -g, so eu-strip will
    leave the unallocated section alone.  (It's very eager.)
- Package the rustlib/ libraries in the base rust.rpm.
- Remove the %{_libdir} libraries that are identical anyway, and
  instead install an entry to rustlib/ in /etc/ld.so.conf.d/.
- Continue the requires/provides filtering.
- Continue shipping *.rlib in rust-std-static.
  - This still works for multilib/cross-compiling too.
This will make it possible now for anyone to link dynamically, with
"rustc -Cprefer-dynamic", but we won't support this officially, and
won't heed compatibility when upgrading rust.  Without the RPM provides,
nothing can be packaged in Fedora with prefer-dynamic.
Does that make sense?  Any other ideas?