Fix crash on macOS 26 due to objc2 signed/unsigned encoding mismatch

[dalehamel]

On macOS 26 (Tahoe), the app panics at startup (when just called via cargo run on main) when winit (via eframe) enumerates NSScreen objects:

thread 'main' panicked at /Users/dalehamel/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/objc2-foundation-0.2.2/src/generated/NSEnumerator.rs:7:1:
invalid message send to -[_TtGCs23_ContiguousArrayStorageCSo8NSScreen_$ countByEnumeratingWithState:objects:count:]: expected return to have type code 'q', but found 'Q'
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'main' panicked at library/core/src/panicking.rs:225:5:
panic in a function that cannot unwind
stack backtrace:
   0:        0x10587e80c - std::backtrace_rs::backtrace::libunwind::trace::h674dcd02776dcc9c
                               at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
   1:        0x10587e80c - std::backtrace_rs::backtrace::trace_unsynchronized::haccaae8fb80e4531
                               at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14
   2:        0x10587e80c - std::sys::backtrace::_print_fmt::h3191fc6495b0a516
                               at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:66:9
   3:        0x10587e80c - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h373e57e2286956dc
                               at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/std/src/sys/backtrace.rs:39:26
   4:        0x10589c638 - core::fmt::rt::Argument::fmt::hcee930b009d69e38
                               at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/fmt/rt.rs:173:76
   5:        0x10589c638 - core::fmt::write::h2c4a0b98b09e3b30
                               at /rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2/library/core/src/fmt/mod.rs:1465:25

The issue seems to be in a dependency ¹:

The objc2 crate's encoding verifier expects a signed type code ('q') for countByEnumeratingWithState:objects:count: but the runtime returns unsigned ('Q'), causing a panic.

This is a known issue in objc2-foundation 0.2.2:

• Objc2 foundation not working with MacOS 26 / Xcode 26 madsmtm/objc2#765
• Swift array count: expected return to have type code 'q', but found 'Q' madsmtm/objc2#566
• Fix: Ignore signed-ness in encoding madsmtm/objc2#567

The fix was released as a feature flag relax-sign-encoding in objc2 0.5.2 (already a transitive dependency via eframe -> winit). Adding objc2 as a direct macOS-only dependency with this feature enabled activates it globally without requiring an eframe version bump.

Note: eframe has not yet upgraded to objc2 0.6.x which includes this fix by default (even latest eframe 0.33.x still uses objc2 0.5.x).

Footnotes

1. FYI I didn't figure this one out myself, I had claude 4.6 do it so there might be a better way, I just needed to unblock myself and get devfiler working again, and thought i'd submit the fix back. ↩

[cla-checker-service]

💚 CLA has been signed

[florianl]

Thanks for the fix 🙏