[ruby-core:101055] [Ruby master Bug#17337] Don't embed Ruby build-time configuration in Ruby

Issue #17337 has been updated by Eregon (Benoit Daloze).


vo.x (Vit Ondruch) wrote in #note-10:
> if I could come in this case to Eventmachine upstream and say "you should not rely on Ruby detected configuration, do your own detection for best results, because Ruby upstream acknowledges the build time and runtime environment might differ", I'd be certainly in better place.

I disagree with that, specifically, C/C++/native extensions should rely on configuration from Ruby libraries such as `mkmf` and `RbConfig`.
Now, those values could reflect the runtime system and not the build system, I would not mind that and it sounds better (but it might be quite difficult to achieve for CRuby).
But I really don't want any native extension to detect its own C/C++ compiler, flags, etc, that leads to many problems and technical debt, notably when trying to compile on TruffleRuby which actually ships its own LLVM toolchain and where `RbConfig::CONFIG["CC/CXX"]` should be used to compile (which just works fine when using `mkmf` and not trying to hack around it).

FWIW TruffleRuby detects most things at runtime, and having a given fixed toolchain avoids so many of these headaches, which e.g. makes it possible to have a single prebuilt Linux binary running on all distributions, with the exception that the openssl C extension is recompiled on the runtime system at installation time because libssl varies too much per platform.

----------------------------------------
Bug #17337: Don't embed Ruby build-time configuration in Ruby
https://bugs.ruby-lang.org/issues/17337#change-88727

* Author: vo.x (Vit Ondruch)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.0dev (2020-11-04 master 704fb0b815) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
When Ruby 3.0 is built without C++ compiler available, subsequent builds of Eventmachine extensions (or any other gems that require C++ compiler) fail:

~~~
... snip ...

"make \"DESTDIR=\""
I. -I/usr/include -I/usr/include/ruby/backward -I/usr/include -I.  -DHAVE_OPENSSL_SSL_H -DHAVE_OPENSSL_ERR_H -DWITH_SSL -DBUILD_FOR_RUBY -DHAVE_RB_THREAD_CALL_WITHOUT_GVL -DHAVE_RB_THREAD_FD_SELECT -DHAVE_TYPE_RB_FDSET_T -DHAVE_RB_WAIT_FOR_SINGLE_FD -DHAVE_RB_TIME_NEW -DHAVE_INOTIFY_INIT -DHAVE_INOTIFY -DHAVE_WRITEV -DHAVE_PIPE2 -DHAVE_ACCEPT4 -DHAVE_CONST_SOCK_CLOEXEC -DOS_UNIX -DHAVE_EPOLL_CREATE -DHAVE_EPOLL -DHAVE_CLOCK_GETTIME -DHAVE_CONST_CLOCK_MONOTONIC_RAW -DHAVE_CONST_CLOCK_MONOTONIC    -fPIC -O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection  -m64 -o binder.o -c binder.cpp
make: I.: No such file or directory
make: [Makefile:237: binder.o] Error 127 (ignored)
~~~

This happens since [1].

I would like to question not just the commit, but the whole principle. Availability of C++ compiler during build of Ruby does not have anything to do with availability of C++ compiler during build of whatever Ruby extension.

Moreover, the machine where Ruby is built might be different from the machine where Ruby is used and the extension is installed. Typical examples are binary Linux distributions. RVM also uses precompiled Ruby binaries if I am not mistaken.

Therefore, I would appreciate if we reconsider embedding Ruby build-time configuration in Ruby and reusing it for Ruby extension build. This would solve the issue of Eventmachine I started with, and also issues such as #14422

Just FTR, to avoid this kind of issues, as a Ruby maintainer on Red Hat platforms, I am considering to ship rbconfig.rb in vendorlib, which would dynamically fix these issues. E.g. set the `CONFIG['CXX']` based on C++ compiler availability during extension build. But I'd like to avoid it, at least as a downstream modification.

[1]: https://github.com/ruby/ruby/commit/50b18e81295ad2d45975e4d8ea1e0c7e85140b97



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