Commit f4ca9eb introduced a regression in the homebrew module where it won't load.
Originally the bail-out code was:
if [[ "$OSTYPE" != (darwin|linux)* ]]; then
return 1
fi
The regression is:
if ! is-darwin || ! is-linux; then
return 1
fi
Fix:
if ! is-darwin && ! is-linux; then
return 1
fi