tcl-tk 9.0.4 (Aqua) never delivers <MouseWheel> events to real hardware scroll input

[priestc]

What's happening

tcl-tk 9.0.4 (Homebrew bottle, Aqua/macOS) never delivers <MouseWheel> events to any Tk widget for real mouse-wheel/scroll input. Scrollbars work fine when dragged, and event_generate("<MouseWheel>", ...) (synthetic events) work and update the UI — but actual OS-delivered scroll input never triggers any <MouseWheel>, <Button-4>, or <Button-5> binding, anywhere.

This was originally found in a real Tkinter app (full write-up here), but I isolated it down to environment-level reproductions with zero app code involved:

1. A bare tk.Tk() window with a single <MouseWheel> binding via bind_all — no scroll events logged when scrolling over the window with a real mouse.
2. A pure Tcl script run directly via wish (no Python/Tkinter at all) with bind all <MouseWheel> {...} — same result, nothing logged.

Both were confirmed via file-logging from inside the event handler (so it's not a stdout-buffering artifact) while actively scrolling with a real mouse over the frontmost, active window.

What I expected

Scrolling with a real mouse/trackpad over any Tk window should fire <MouseWheel> (or <Button-4>/<Button-5>) bindings, same as it does on other Tk installs (e.g. older tcl-tk 8.6 builds, or system Tk elsewhere).

Environment

brew config output:

HOMEBREW_VERSION: 6.0.15
ORIGIN: https://github.com/Homebrew/brew
HEAD: 7b0f22a4ab77567edef114c8dfc423fb96e2fbaa
Last commit: 7 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: 21.0.0 build 2100
Git: 2.50.1 => /Applications/Xcode.app/Contents/Developer/usr/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.5.2-arm64
CLT: 26.2.0.0.1.1764812424
Xcode: 26.6
Metal Toolchain: N/A
Rosetta 2: false

tcl-tk: 9.0.4 (installed via brew install tcl-tk), confirmed the running interpreter links against /opt/homebrew/opt/tcl-tk/lib/libtcl9tk9.0.dylib (via otool -L on _tkinter.cpython-314-darwin.so from a python-tk@3.14 install).

I'm not filing this as an Issue against homebrew-core because brew doctor on this machine has a few unrelated warnings (deprecated rar cask, outdated CLT release, deprecated icu4c@77 — none of which relate to Tk or scrolling), and I didn't want to make unrelated system changes just to satisfy the issue template's clean-doctor requirement. Posting here first in case anyone recognizes this or knows whether it's actually a Tk-core Aqua regression (in which case it'd need to go to the Tcl/Tk Fossil tracker at core.tcl-lang.org rather than here) versus something specific to the Homebrew build/patches.

Steps to reproduce

brew install tcl-tk
# in a Python venv with python-tk@3.14 (or run a pure Tcl script with `wish`)
python3 -c "
import tkinter as tk
root = tk.Tk()
root.bind_all('<MouseWheel>', lambda e: print('GOT', e.delta))
root.mainloop()
"

Then scroll over the window with a real mouse — nothing prints. event_generate('<MouseWheel>', delta=-3) from a script does trigger the callback, so the binding itself is registered correctly; it's real hardware-originated events specifically that never arrive.

Happy to provide more diagnostics (e.g. downgrading to tcl-tk@8 to confirm whether it's 9.0-specific) if useful.

[SMillerDev]

Why not ask the tcl-tk developers? Chances are they are much better at debugging this than anyone looking here.