I get the following error when trying to upgrade Ruby to 2.6.7:
$ rbenv install 2.6.7
...
implicit declaration of function 'rb_native_mutex_destroy' is invalid in C99
vm.c:2489:34: warning: expression does not compute the number of elements in this array; element type is 'const int', not 'VALUE' (aka 'unsigned long') [-Wsizeof-array-div]
sizeof(ec->machine.regs) / sizeof(VALUE));
~~~~~~~~~~~~~~~~ ^
vm.c:2489:34: note: place parentheses around the 'sizeof(VALUE)' expression to silence this warning
Is there a fix?
Yes, this is a known issue upstream: https://bugs.ruby-lang.org/issues/17777
ruby-build is also tracking this issue: https://github.com/rbenv/ruby-build/issues/1489
The work around is to run the following code, and install ruby 2.6.7 again:
$ export warnflags=-Wno-error=implicit-function-declaration
$ rbenv install 2.6.7
-or-
$ CFLAGS="-Wno-error=implicit-function-declaration" rbenv install 2.6.7
Looks like this can also impact gem installation with native extensions (mysql2 is one of those):
gem install <GEMNAME> -- --with-cflags="-Wno-error=implicit-function-declaration"
Additionally to following Gavin's answer,
I had to reinstall readline. brew reinstall readline