New crash handler in macOS?

[richlander]

This experience seems to be new. I wrote a test app with an intentional crash scenario to test something. This is what I saw. Not a problem, just (A) is this new?, and (B) FYI.

[vcsjones]

This looks like the Swift crash handler. https://www.swift.org/blog/swift-5.9-backtraces/

The post goes on to say that the debugger is off by default for macOS, maybe they turned it on by default in macOS 26.

If we don't like it I suppose we could set environment variable SWIFT_BACKTRACE to enable=no on start up, if the environment variable is unset. That way folks can turn it on if they want.

[vcsjones]

From Apple's docs:

Note that the runtime will not install its signal handlers for a signal if it finds that there is already a handler for that signal. Similarly if something else has already configured an alternate signal stack, it will leave that stack alone.

This is interesting and I wonder if Apple's exception handling will collide with our own, since it mentions configuring alternate stacks.

cc @janvorli

[richlander]

@hoyosjs @steveisok

[richlander]

FYI: I am now one beta build back. Another came out (I think) last week. I'm in the middle of a project and have been delaying upgrading until I get to a clean spot (and can push my changes). It's possible that the beheavior changes in the next build. perhaps someone else has that installed.

[richlander]

For kicks, this is the code I was running: https://gist.github.com/richlander/d5f8cf2b6fb0fce45a336a387c3858ff

[vcsjones]

I can reproduce this on Preview 7. Any second change managed exception causes it. A simple 1-line program:

throw new Exception("hello!");

Will invoke the Swift debugger.

This is with .NET 10 preview 7 and macOS 26 preview 7. I am not using a debug build of the runtime.

Doing SWIFT_BACKTRACE="enable=no" dotnet run does indeed disable the swift backtrace handler.

[jeffhandley]

@jkotas / @agocke Where in the product would we go about disabling this by default? I presume we'd need to introduce our own ENV var to disable us disabling it too.

[vcsjones]

Where in the product would we go about disabling this by default?

I don't know how easy this is to do by environment variable. This needs to be done very early in application startup - before the managed Main. I can't disable it programmatically from my own program.