Installing from source no longer possible with tap checked out locally

[slhck]

Output of brew config

HOMEBREW_VERSION: 4.6.11-107-g23d4a36
ORIGIN: https://github.com/Homebrew/brew
HEAD: 23d4a36a290b85d1c93a981ebe45d7b382650108
Last commit: 3 hours ago
Branch: main
Core tap HEAD: 811a11fa7183c7cf51a339704f10c52669a8b9c5
Core tap last commit: 31 minutes ago
Core tap JSON: 21 Sep 18:18 UTC
Core cask tap HEAD: 27581aecbeec188a426f3509d0af2551030af881
Core cask tap last commit: 74 minutes ago
Core cask tap JSON: 21 Sep 18:18 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.MnOy7I4j6N/org.xquartz:0
HOMEBREW_EDITOR: vim
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_MAKE_JOBS: 8
HOMEBREW_SORBET_RUNTIME: set
Homebrew Ruby: 3.4.6 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.4.6/bin/ruby
CPU: octa-core 64-bit arm_firestorm_icestorm
Clang: 17.0.0 build 1700
Git: 2.51.0 => /opt/homebrew/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 15.6.1-arm64
CLT: 16.4.0.0.1.1747106510
Xcode: 26.0
Rosetta 2: false

Output of brew doctor

N/A

Description of issue

I used to be able to test changes to my Homebrew tap by simply installing from source:

brew install --build-from-source ./Formula/ffmpeg.rb
Error: Homebrew requires formulae to be in a tap, rejecting:
  ./Formula/ffmpeg.rb (/Users/werner/Documents/Software/homebrew-ffmpeg/homebrew-ffmpeg/Formula/ffmpeg.rb)

To create a tap, run e.g.
  brew tap-new <user|org>/<repository>
To create a formula in a tap run e.g.
  brew create <url> --tap=<user|org>/<repository>

Now that leads to the above error.

I have the tap checked out in a different folder locally to make and push changes to the formula.

What is the suggested alternative?

In the docs it says:

Test your formulae: Before pushing changes, test your formulae locally with brew install --build-from-source user/repository/formula

But this would refer to the tap I have in /opt/homebrew/Library/Taps/homebrew-ffmpeg – correct?
Is is recommended to edit files directly in there?

[ZhongRuoyu]

But this would refer to the tap I have in /opt/homebrew/Library/Taps/homebrew-ffmpeg – correct?
Is is recommended to edit files directly in there?

Yes, Homebrew no longer supports installing a formula outside taps, and the recommended way is to place the tap repository at the expected location. You need to move your tap to /opt/homebrew/Library/Taps/homebrew-ffmpeg/homebrew-ffmpeg.