Issue #19143 has been updated by MSP-Greg (Greg L). @nobu Yes, I agree, it might be very helpful when one has more than one platform installed and uses `--user-install`. As in `Gem.install_extension_in_lib`, also [Gem::Ext::ExtConfBuilder](https://github.com/ruby/ruby/blob/master/lib/rubygems/ext/ext_conf_builder.r...). I overwrite my Windows Ruby master installs daily, so I always use `--user-install`. Maybe issues with existing extension gems that load with `require_relative`, and also pre-compiled gems? ---------------------------------------- Bug #19143: Windows - bundled extension gems compile, but don't copy *.so files to lib folder https://bugs.ruby-lang.org/issues/19143#change-100408 * Author: MSP-Greg (Greg L) * Status: Closed * Priority: Normal * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- Just finished updating ruby-loco's mswin build to use a system similar to the ucrt & mingw builds. Confirmed something I noticed previously, and also occurs with the RubyInstaller2 head build. On Windows, bundled extension gems (debug, rbs) compile their extension in the `ext` folder, but do not copy them to the `lib` folder. So, the *.so file is created, but not copied. I think this was working correctly on Ruby 3.1? -- https://bugs.ruby-lang.org/