ruby with jemalloc won't configure - homebrew/OSX/montery/m1/arm(?) - ruby

Question

OSX/Monterey/M1/Arm/Homebrew: can't for the life of me get this to work:
./configure --with-jemalloc
It dies with
checking jemalloc/jemalloc.h presence... no
configure: error: jemalloc requested but not found
even though it's right there in: /opt/homebrew/Cellar/jemalloc/5.2.1_1/include/jemalloc/jemalloc.js.
brew --prefix jemalloc and jemalloc-config --includedir all looks correct.
I've tried various versions of:
export RUBY_CONFIGURE_OPTS="--with-jemalloc-include=$(brew --prefix jemalloc)/include
and/or
./configure --with-jemalloc-include=$(brew --prefix jemalloc)/include
but no dice. Not even sure those env vars/flags are respected by ruby or if they're some rvm/rbenv/ruby-build thing.
I'm down to doing all my testing directly with ruby's configure and not a rvm/build tool.

Answer 1

Try the following:
❯ export HOMEBREW_PREFIX=$(brew --prefix)
❯ export CPPFLAGS="$CPPFLAGS -I $HOMEBREW_PREFIX/include"
❯ export LDFLAGS="$LDFLAGS -L $HOMEBREW_PREFIX/lib"
❯ cd ruby-2.7.6 && ./configure --with-jemalloc
❯ make && make install

Answer 2

This worked using RVM:
# Install jemalloc first
brew install jemalloc
# Install using RVM:
rvm install 3.2.1 --with-jemalloc --with-cppflags="-I$(brew --prefix)/include" -E "LDFLAGS=-L$(brew --prefix)/lib"
It seems that --with-cppflags works as expected, but it's being overwritten by the internal RVM flags passed in, so --with-ldflags does nothing. That's why we pass in the -E flag (as an enviroment variable) instead.