brew 3.0 building everything from source on Intel Big Sur

[rgacote]

I'm running on an Intel iMac, Big Sur 11.2, with brew 3.0.0 (git revision d01147). My brew --prefix is /usr/local/homebrew.
Everything builds from source because any brew install gives the following warning:

- HOMEBREW_CELLAR: /usr/local/Cellar (yours is /usr/local/homebrew/Cellar)
- HOMEBREW_PREFIX: /usr/local (yours is /usr/local/homebrew)

I'm doing an upgrade from a working brew 2.x so perhaps there's something left behind.
Tried uninstalling, removing the /usr/local/homebrew directories and also the brew path that was in my .zshrc.

After a clean install of 3.0 my brew --prefix is still /usr/local/homebrew and everything tries to build from source.

• Is there some additional hidden file left over from the 2.x install I've not removed?
• Is there something obvious I've missed about homebrew and this OS?

I've looked through the other --preview related discussions and tickets and not found one that looks relevant to the issue I'm having.

If it helps, the projects I'm trying to install are:

• mercurial
• plantuml

Thanks

[rgacote]

After spending a few hours on this, of course it starts working as soon as I publicly ask a question... All bottles are pouring properly.

I think the only thing that changed was that I restarted my iTerm session. Perhaps there was an environment variable left over that was causing the problem?

I'll leave this as a hint for future problem solving:

• Completely uninstall the prior homebrew 2.x.
• Ensure there are no brew path or other references in your .bashrc/.bash_profile/.zshrc, etc.
• Restart your terminal application.
• Install 3.0 clean
• Ensure brew --prefix is usr/local before installing anything.