brew bundle install with tap & root-level formula in that tap reports failure but succeeds

### `brew doctor` output ```shell Please note that these warnings are just used to help the Homebrew maintainers with debugging if you file an issue. If everything you use Homebrew for is working fine: please don't worry or file an issue; just ignore this. Thanks! Warning: Your Xcode (26.1.1) is outdated. Please update to Xcode 26.3 (or delete it). Xcode can be updated from the App Store. This is a Tier 2 configuration: https://docs.brew.sh/Support-Tiers#tier-2 You can report issues with Tier 2 configurations to Homebrew/* repositories! Read the above document before opening any issues or PRs. ``` I have also reproduced this on a machine with no warnings from `brew doctor`, this is just the output I have the easiest access to copy-paste ### Verification - [x] I ran `brew update` twice and am still able to reproduce my issue. - [x] My "`brew doctor` output" above says `Your system is ready to brew` or a definitely unrelated `Tier` message. - [x] This issue's title and/or description do not reference a single formula e.g. `brew install wget`. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead. ### `brew config` output ```shell HOMEBREW_VERSION: 6.0.0 ORIGIN: https://github.com/Homebrew/brew HEAD: 3d9e344622974a7f96da927fd0407e08581eb437 Last commit: 8 hours ago Branch: stable Core tap: N/A Core cask tap: N/A HOMEBREW_PREFIX: /opt/homebrew HOMEBREW_CASK_OPTS: [] HOMEBREW_DOWNLOAD_CONCURRENCY: 24 HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set HOMEBREW_MAKE_JOBS: 12 HOMEBREW_REQUIRE_TAP_TRUST: set Homebrew Ruby: 4.0.5 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.5_1/bin/ruby CPU: dodeca-core 64-bit arm_brava Clang: 17.0.0 build 1700 Git: 2.50.1 => /Applications/Xcode.app/Contents/Developer/usr/bin/git Curl: 8.7.1 => /usr/bin/curl macOS: 26.5-arm64 CLT: 26.5.0.0.1777544298 Xcode: 26.1.1 Metal Toolchain: N/A Rosetta 2: false ``` ### What were you trying to do (and why)? I'm attempting to set up a `Brewfile` for reproducible installation of development environments, and I need to be able to install packages from third-party taps. One of the taps in question has its formulas at the root directory of the repo. Attempting to do so as of Homebrew 6 now experiences an error. ### What happened (include all command output)? `brew bundle install` reports 3 warnings, a failure, and exits with a non-zero status code. However, the installation is actually successful and on a re-run there is nothing to be done ``` ❯ brew bundle install Warning: 'metalbear-co/mirrord/mirrord' formula is unreadable: No available formula with the name "metalbear-co/mirrord/mirrord". This command requires the tap metalbear-co/mirrord. If you trust this tap, tap it explicitly and then try again: brew tap metalbear-co/mirrord Warning: 'metalbear-co/mirrord/mirrord' formula is unreadable: No available formula with the name "metalbear-co/mirrord/mirrord". This command requires the tap metalbear-co/mirrord. If you trust this tap, tap it explicitly and then try again: brew tap metalbear-co/mirrord Tapping metalbear-co/mirrord Installing metalbear-co/mirrord/mirrord Warning: 'metalbear-co/mirrord/mirrord' formula is unreadable: No available formula with the name "metalbear-co/mirrord/mirrord". Installing metalbear-co/mirrord/mirrord has failed! `brew bundle` failed! 1 Brewfile dependency failed to install ~/Desktop ❯ brew list | grep mirrord mirrord ~/Desktop ❯ brew bundle install Using metalbear-co/mirrord Using metalbear-co/mirrord/mirrord `brew bundle` complete! 2 Brewfile dependencies now installed. ``` ### What did you expect to happen? I'd expect: - No errors to be logged, as the Brewfile is tapping & trusting the tap - The command to exit with no error and a 0 status code, as it actually installed successfully Alternatively, if root-level formulas are not supported I'd expect it to error out entirely, rather than installing successfully ### Step-by-step reproduction instructions (by running `brew` commands) Write the following to a Brewfile (origin provided because of #22668): ```ruby tap "metalbear-co/mirrord", "https://github.com/metalbear-co/homebrew-mirrord", trusted: true brew "metalbear-co/mirrord/mirrord", trusted: true ``` Install the brewfile with `brew bundle install` It will report 3 warning, a failure, and exit with a non-zero status, but will have successfully installed the tap and the formula