Auto merge of #130846 - ChrisDenton:revert-break, r=Noratrieb

Revert Break into the debugger on panic (129019)

This was talked about a bit at a recent libs meeting. While I think experimenting with this is worthwhile, I am nervous about this new behaviour reaching stable. We've already reverted on one tier 1 platform (Linux, #130810) which means we have differing semantics on different tier 1 platforms. Also the fact it triggers even when `catch_unwind` is used to catch the panic means it can be very noisy in some projects.

At the very least I think it could use some more discussion before being instantly stable. I think this could maybe be re-landed with an environment variable to control/override the behaviour. But that part would likely need a libs-api decision.

cc `@workingjubilee` `@kromych`

library/std/src/panicking.rs

@@ -23,8 +23,8 @@ use crate::mem::{self, ManuallyDrop};
 use crate::panic::{BacktraceStyle, PanicHookInfo};
 use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sync::{PoisonError, RwLock};
+use crate::sys::backtrace;
 use crate::sys::stdio::panic_output;
-use crate::sys::{backtrace, dbg};
 use crate::{fmt, intrinsics, process, thread};
 
 // Binary interface to the panic runtime that the standard library depends on.
@@ -859,29 +859,13 @@ pub fn rust_panic_without_hook(payload: Box<dyn Any + Send>) -> ! {
 #[cfg_attr(not(test), rustc_std_internal_symbol)]
 #[cfg(not(feature = "panic_immediate_abort"))]
 fn rust_panic(msg: &mut dyn PanicPayload) -> ! {
-    // Break into the debugger if it is attached.
-    // The return value is not currently used.
-    //
-    // This function isn't used anywhere else, and
-    // using inside `#[panic_handler]` doesn't seem
-    // to count, so a warning is issued.
-    let _ = dbg::breakpoint_if_debugging();
-
     let code = unsafe { __rust_start_panic(msg) };
     rtabort!("failed to initiate panic, error {code}")
 }
 
 #[cfg_attr(not(test), rustc_std_internal_symbol)]
 #[cfg(feature = "panic_immediate_abort")]
 fn rust_panic(_: &mut dyn PanicPayload) -> ! {
-    // Break into the debugger if it is attached.
-    // The return value is not currently used.
-    //
-    // This function isn't used anywhere else, and
-    // using inside `#[panic_handler]` doesn't seem
-    // to count, so a warning is issued.
-    let _ = dbg::breakpoint_if_debugging();
-
     unsafe {
         crate::intrinsics::abort();
     }

library/std/src/sys/mod.rs

@@ -11,7 +11,6 @@ mod personality;
 pub mod anonymous_pipe;
 pub mod backtrace;
 pub mod cmath;
-pub mod dbg;
 pub mod exit_guard;
 pub mod os_str;
 pub mod path;