Stumped by bundler native extension issue, help appreciated!

[Woody Peterson]

I asked the Bundler contributors, and they don't know what the issue could be, so I thought someone familiar with the C code in rgeo might have a clue.

Basically, I just upgraded from ruby 2.3 to ruby 2.6 on heroku, which required rebuilding my native extensions. RGeo is somehow not getting the native extensions built correctly when ran through bundler, but does when ran through the gem command:

-----

$ export BUNDLE_BUILD__RGEO="--with-opt-dir=.heroku/vendor --with-geos-config=.heroku/vendor/bin/geos-config"

$ gem uninstall -i /app/vendor/bundle/ruby/2.6.0 rgeo

$ bundle install --verbose

[...]

Installing rgeo 0.6.0 with native extensions

Building native extensions with: '--with-opt-dir=.heroku/vendor --with-geos-config=.heroku/vendor/bin/geos-config'

[...]

$ ./bin/rails c

> RGeo::Geos.supported?

false

$ gem uninstall -i /app/vendor/bundle/ruby/2.6.0 rgeo

$ gem install -i /app/vendor/bundle/ruby/2.6.0/ rgeo -v 0.6.0 -- $BUNDLE_BUILD__RGEO

Fetching rgeo-0.6.0.gem

Building native extensions with: '--with-opt-dir=.heroku/vendor --with-geos-config=.heroku/vendor/bin/geos-config'

[...]

$ ./bin/rails c

> RGeo::Geos.supported?

true

-----

So this might be a bundler issue, but obviously there's something needed by the C extension it's not getting, so maybe someone here will have an idea where to look?

Thanks,

-Woody