Why am I seeing casks in brew update on Linux?

[iandol]

Additional Info

• I am using Windows Subsystem for Linux

Output of brew config

▷ brew config
HOMEBREW_VERSION: 4.0.13-17-g9912dca
ORIGIN: https://github.com/Homebrew/brew
HEAD: 9912dcab7c25b5aa90f4a1c73351e4213b90cf35
Last commit: 6 hours ago
Core tap origin: https://github.com/Homebrew/homebrew-core
Core tap HEAD: aebee05a30008769b04332d0c47e05e337b63c4e
Core tap last commit: 3 months ago
Core tap branch: master
Core tap JSON: 14 Apr 00:21 UTC
HOMEBREW_PREFIX: /home/linuxbrew/.linuxbrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DISPLAY: :1
HOMEBREW_EDITOR: nvim
HOMEBREW_MAKE_JOBS: 16
all_proxy: 127.0.0.1:20171
ftp_proxy: 127.0.0.1:20171
http_proxy: 127.0.0.1:20171
https_proxy: 127.0.0.1:20171
no_proxy: localhost, 127.0.0.1, ::1
Homebrew Ruby: 2.6.10 => /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.10_1/bin/ruby
CPU: 16-core 64-bit skylake
Clang: N/A
Git: 2.34.1 => /bin/git
Curl: 7.81.0 => /bin/curl
Kernel: Linux 5.19.0-1022-lowlatency x86_64 GNU/Linux
OS: Ubuntu 22.04.2 LTS (jammy)
Host glibc: 2.35
/usr/bin/gcc: 11.3.0
/usr/bin/ruby: N/A
glibc: N/A
gcc@11: N/A
gcc: N/A
xorg: N/A

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: 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/LabJackM.h
  /usr/local/include/labjackusb.h
Exception: brew exited with 1
[tty 42]:1:1: brew doctor

Description of issue

When I do a brew update I am seeing a section for casks, but I thought Linux didn't support casks and when I triy to brew info one of these it tells me there is no formula with that name:

▶︎ brew update; brew outdated; brew upgrade; brew cleanup
==> Downloading https://ghcr.io/v2/homebrew/portable-ruby/portable-ruby/blobs/sha256:68923daf3e139482b977c3deba63a3b54ea37bb5f716482948878819ef911bad
######################################################################## 100.0%
==> Pouring portable-ruby-2.6.10_1.x86_64_linux.bottle.tar.gz
==> Updated Homebrew from 4.0.12 (80372686f) to 4.0.13 (9912dcab7).
Updated 4 taps (linuxbrew/fonts, rsteube/tap, homebrew/core and homebrew/cask).
==> New Formulae
form           hck            resvg          sad            vvdec          vvenc
==> New Casks
bluos-controller                              logitech-g-hub
canon-eos-utility                             logitech-options
corsair-icue                                  segger-jlink
displaylink                                   sony-ps-remote-play
elgato-stream-deck                            tachidesk-sorayomi
elgato-video-capture                          toshiba-color-mfp
elgato-wave-link                              ubiquiti-unifi-controller
konica-minolta-bizhub-c750i-driver            yubico-yubikey-manager
logitech-camera-settings
==> Outdated Formulae
carapace                       libxml2                        starship

▷ brew tap
homebrew/core
linuxbrew/fonts
rsteube/tap

[cho-m]

I think the JSON API just updates both Formula and Cask JSON files for all OS - https://github.com/Homebrew/brew/blob/master/Library/Homebrew/cmd/update.sh#L778

    for formula_or_cask in formula cask

If OS can be checked in script, then it may be possible to skip this for cask on Linux.

EDIT: also need to skip Homebrew::API::Cask.write_names in https://github.com/Homebrew/brew/blob/master/Library/Homebrew/cmd/update-report.rb#L151 to avoid fetch JSON inside Ruby code.