Unexpected/unexplained package upgrades for a brew upgrade with specific packages

[razzius]

Output of brew config

HOMEBREW_VERSION: 6.0.18
ORIGIN: https://github.com/Homebrew/brew
HEAD: 5b90e281d4e0c8fbd6ca4d8358276fb305b8d0bd
Last commit: 6 days ago
Branch: stable
Core tap: N/A
Core cask tap: N/A
HOMEBREW_PREFIX: /opt/homebrew
Homebrew Ruby: 4.0.6 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.6/bin/ruby
CPU: deca-core 64-bit arm_donan
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: 15.7.7-arm64
CLT: 26.2.0.0.1.1764812424
Xcode: 26.3
Metal Toolchain: N/A
Rosetta 2: false

Output of brew doctor

$ brew doctor
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: Some installed casks are deprecated or disabled.
You should find replacements for the following casks:
gstreamer-runtime
  intellij-idea-ce
  lego-mindstorms-ev3
  wine-stable

Warning: A newer Command Line Tools release is available.
Update them from Software Update in System 设置.

If that doesn't show you any updates, run:
  sudo rm -rf /Library/Developer/CommandLineTools
  sudo xcode-select --install

Alternatively, manually download them from:
  https://developer.apple.com/download/all/.
You should download the Command Line Tools for Xcode 26.3.

Warning: Some installed formulae are deprecated or disabled.
You should find replacements for the following formulae:
    icu4c@77

Warning: Unbrewed dylibs were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected dylibs:
  /usr/local/lib/libcrypto-ni.3.dylib
  /usr/local/lib/libnotcurses++.3.0.17.dylib
  /usr/local/lib/libnotcurses-core.3.0.17.dylib
  /usr/local/lib/libnotcurses-ffi.3.0.17.dylib
  /usr/local/lib/libnotcurses.3.0.17.dylib
  /usr/local/lib/libssl-ni.3.dylib

Warning: Unbrewed header files were found in /usr/local/include.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected header files:
  /usr/local/include/notcurses/*

Warning: Unbrewed '.pc' files were found in /usr/local/lib/pkgconfig.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected '.pc' files:
  /usr/local/lib/pkgconfig/notcurses++.pc
  /usr/local/lib/pkgconfig/notcurses-core.pc
  /usr/local/lib/pkgconfig/notcurses-ffi.pc
  /usr/local/lib/pkgconfig/notcurses.pc

Warning: Unbrewed static libraries were found in /usr/local/lib.
If you didn't put them there on purpose they could cause problems when
building Homebrew formulae and may need to be deleted.

Unexpected static libraries:
  /usr/local/lib/libnotcurses++.a
  /usr/local/lib/libnotcurses-core.a
  /usr/local/lib/libnotcurses.a

Warning: You have unlinked kegs in your Cellar.
Leaving kegs unlinked can lead to build-trouble and cause formulae that depend on
those kegs to fail to run properly once built.

Run `brew link` on these:
  docker

Warning: Homebrew's "sbin" was not found in your PATH but you have installed
formulae that put executables in /opt/homebrew/sbin.

Consider setting your PATH for example like so:
  fish_add_path /opt/homebrew/sbin
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!
  https://docs.brew.sh/Troubleshooting
Read the above document before opening any issues or PRs.

Description of issue

I was running a brew upgrade with a few packages I thought would be quick upgrades, and read the output of "==> Would upgrade <...> dependencies for <...>". Confusingly, llvm and rust were listed amoung the "would be upgraded", although it wasn't part of the "==> Would upgrade/install" messages. Take a look:

$ brew upgrade go hugo node php ruby vim tmux unbound z3 docker balena-cli
==> Downloading bottle manifests
✔︎ Bottle Manifest z3 (5.1.0)                                                                             Downloaded   15.7KB/ 15.7KB
✔︎ Bottle Manifest docker (29.7.2)                                                                        Downloaded   15.3KB/ 15.3KB
✔︎ Bottle Manifest go (1.27.0)                                                                            Downloaded   14.8KB/ 14.8KB
✔︎ Bottle Manifest unbound (1.26.0)                                                                       Downloaded   44.8KB/ 44.8KB
✔︎ Bottle Manifest ruby (4.0.6_1)                                                                         Downloaded   46.9KB/ 46.9KB
✔︎ Bottle Manifest tmux (3.7c)                                                                            Downloaded   49.9KB/ 49.9KB
✔︎ Bottle Manifest hugo (0.165.0)                                                                         Downloaded   14.8KB/ 14.8KB
✔︎ Bottle Manifest vim (9.2.0950)                                                                         Downloaded   55.5KB/ 55.5KB
✔︎ Bottle Manifest node (26.7.0)                                                                          Downloaded  176.2KB/176.2KB
✔︎ Bottle Manifest balena-cli (25.2.5)                                                                    Downloaded  238.7KB/238.7KB
✔︎ Bottle Manifest php (8.5.9)                                                                            Downloaded  349.5KB/349.5KB
==> Would upgrade 3 dependencies for node:
libnghttp2  1.69.0 -> 1.70.0
llhttp      9.4.2  -> 9.4.3
simdjson    4.6.4  -> 4.6.7
==> Would upgrade 4 dependencies for balena-cli:
libffi      3.7.1  -> 3.8.0
libnghttp2  1.69.0 -> 1.70.0
llhttp      9.4.2  -> 9.4.3
simdjson    4.6.4  -> 4.6.7
==> Would install 1 dependency for tmux:
jemalloc 5.3.1
==> Would upgrade 1 dependency for unbound:
libnghttp2 1.69.0 -> 1.70.0
==> Would upgrade 13 outdated packages
node        26.5.0_1 -> 26.7.0 (21.7MB)
balena-cli  25.2.0   -> 25.2.5 (57.2MB)
hugo        0.164.0  -> 0.165.0 (28.4MB)
php         8.5.8    -> 8.5.9 (29.3MB)
ruby        4.0.6    -> 4.0.6_1 (17MB)
vim         9.2.0850 -> 9.2.0950 (14.7MB)
tmux        3.7b     -> 3.7c (544.2KB)
unbound     1.25.2   -> 1.26.0 (3MB)
z3          4.16.0   -> 5.1.0 (13.7MB)
docker      29.6.2   -> 29.7.2 (9.3MB)
go          1.26.5   -> 1.27.0 (67.6MB)
llvm        22.1.8   -> 22.1.8_2 (453.0MB)
rust        1.97.1   -> 1.98.0 (110MB)
==> Do you want to proceed with the upgrade? [y/n]

I understand this is far from the minimally reproducible example, and it's also possible I'm simply misunderstanding something. But I was surprised to see llvm (a large download) among the packages to be upgraded without it being listed as a dependency as a dependency of any of those packages.

Am I misunderstanding something, or is it a bug in brew?

[p-linnane]

This is expected and is covered by this FAQ entry. In this case, llvm depends on the explicitly requested z3, and the installed rust 1.97.1 depended on llvm, so Homebrew follows the reverse-dependent chain and upgrades both. The “Would upgrade dependencies for …” sections list forward dependencies; these are reverse dependents, so they only appear in the final upgrade summary.

[razzius]

Thanks for that explanation @p-linnane.

Do you think it would be worth putting in a feature request for the brew upgrade output to include the reverse dependencies as well?

[p-linnane]

You're free to open a PR and we'll review it.

[MikeMcQuaid]

I've opened a PR in Homebrew/brew#23691 to improve this output