Auto merge of #122565 - Zoxc:atomic-panic-msg, r=the8472

Try to write the panic message with a single `write_all` call

This writes the panic message to a buffer before writing to stderr. This allows it to be printed with a single `write_all` call, preventing it from being interleaved with other outputs. It also adds newlines before and after the message ensuring that only the panic message will have its own lines.

Before:
```
thread 'thread 'thread 'thread 'thread '<unnamed>thread 'thread 'thread 'thread '<unnamed><unnamed>thread '<unnamed>' panicked at ' panicked at <unnamed><unnamed><unnamed><unnamed><unnamed>' panicked at <unnamed>' panicked at src\heap.rssrc\heap.rs'
panicked at ' panicked at ' panicked at ' panicked at ' panicked at src\heap.rs' panicked at src\heap.rs::src\heap.rssrc\heap.rssrc\heap.rssrc\heap.rssrc\heap.rs:src\heap.rs:455455:::::455:455::455455455455455:455:99:::::9:9:
:
999:
999:
assertion failed: size <= (*queue).block_size:
:
assertion failed: size <= (*queue).block_size:
assertion failed: size <= (*queue).block_size:
:
:
assertion failed: size <= (*queue).block_sizeassertion failed: size <= (*queue).block_sizeassertion failed: size <= (*queue).block_size

assertion failed: size <= (*queue).block_size
assertion failed: size <= (*queue).block_sizeassertion failed: size <= (*queue).block_sizeerror: process didn't exit successfully: `target\debug\direct_test.exe` (exit code: 0xc0000409, STATUS_STACK_BUFFER_OVERRUN)
```
After:
```

thread '<unnamed>' panicked at src\heap.rs:455:9:
assertion failed: size <= (*queue).block_size

thread '<unnamed>' panicked at src\heap.rs:455:9:
assertion failed: size <= (*queue).block_size

thread '<unnamed>' panicked at src\heap.rs:455:9:
assertion failed: size <= (*queue).block_size

error: process didn't exit successfully: `target\debug\direct_test.exe` (exit code: 0xc0000409, STATUS_STACK_BUFFER_OVERRUN)
```

---

try-jobs: x86_64-gnu-llvm-18

Author: bors

tests/fail/function_calls/exported_symbol_bad_unwind1.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind1.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/function_calls/exported_symbol_bad_unwind2.both.stderr

@@ -1,7 +1,9 @@
+
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

tests/fail/function_calls/exported_symbol_bad_unwind2.definition.stderr

@@ -1,7 +1,9 @@
+
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

tests/fail/function_calls/exported_symbol_bad_unwind2.extern_block.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/function_calls/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/function_calls/return_pointer_on_unwind.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/function_calls/return_pointer_on_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/intrinsics/uninit_uninhabited_type.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 aborted execution: attempted to instantiate uninhabited type `!`
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/intrinsics/zero_fn_ptr.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 aborted execution: attempted to zero-initialize type `fn()`, which is invalid
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/panic/abort_unwind.stderr

@@ -1,7 +1,9 @@
+
 thread 'main' panicked at tests/fail/panic/abort_unwind.rs:LL:CC:
 PANIC!!!
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

tests/fail/panic/bad_unwind.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/panic/bad_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/panic/double_panic.stderr

@@ -1,10 +1,13 @@
+
 thread 'main' panicked at tests/fail/panic/double_panic.rs:LL:CC:
 first
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at tests/fail/panic/double_panic.rs:LL:CC:
 second
 stack backtrace:
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a destructor during cleanup
 thread caused non-unwinding panic. aborting.

tests/fail/panic/panic_abort1.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/panic/panic_abort1.rs:LL:CC:
 panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/panic/panic_abort2.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/panic/panic_abort2.rs:LL:CC:
 42-panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/panic/panic_abort3.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/panic/panic_abort3.rs:LL:CC:
 panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/panic/panic_abort4.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/fail/panic/panic_abort4.rs:LL:CC:
 42-panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/panic/tls_macro_const_drop_panic.stderr

@@ -1,3 +1,4 @@
+
 thread $NAME panicked at tests/fail/panic/tls_macro_const_drop_panic.rs:LL:CC:
 ow
 fatal runtime error: thread local panicked on drop

tests/fail/panic/tls_macro_drop_panic.stderr

@@ -1,3 +1,4 @@
+
 thread $NAME panicked at tests/fail/panic/tls_macro_drop_panic.rs:LL:CC:
 ow
 fatal runtime error: thread local panicked on drop

tests/fail/terminate-terminator.stderr

@@ -1,9 +1,11 @@
 warning: You have explicitly enabled MIR optimizations, overriding Miri's default which is to completely disable them. Any optimizations may hide UB that Miri would otherwise detect, and it is not necessarily possible to predict what kind of UB will be missed. If you are enabling optimizations to make Miri run faster, we advise using cfg(miri) to shrink your workload instead. The performance benefit of enabling MIR optimizations is usually marginal at best.
 
+
 thread 'main' panicked at tests/fail/terminate-terminator.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

tests/fail/unwind-action-terminate.stderr

@@ -1,7 +1,9 @@
+
 thread 'main' panicked at tests/fail/unwind-action-terminate.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

tests/panic/alloc_error_handler_hook.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/alloc_error_handler_hook.rs:LL:CC:
 alloc error hook called
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/alloc_error_handler_panic.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at RUSTLIB/std/src/alloc.rs:LL:CC:
 memory allocation of 4 bytes failed
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/div-by-zero-2.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/div-by-zero-2.rs:LL:CC:
 attempt to divide by zero
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/function_calls/exported_symbol_good_unwind.stderr

@@ -1,8 +1,11 @@
+
 thread 'main' panicked at tests/panic/function_calls/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at tests/panic/function_calls/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic
+
 thread 'main' panicked at tests/panic/function_calls/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic

tests/panic/mir-validation.stderr

@@ -1,3 +1,4 @@
+
 thread 'rustc' panicked at compiler/rustc_mir_transform/src/validate.rs:LL:CC:
 broken MIR in Item(DefId) (after phase change to runtime-optimized) at bb0[1]:
 place (*(_2.0: *mut i32)) has deref as a later projection (it is only permitted as the first projection)

tests/panic/oob_subslice.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/oob_subslice.rs:LL:CC:
 range end index 5 out of range for slice of length 4
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/overflowing-lsh-neg.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/overflowing-lsh-neg.rs:LL:CC:
 attempt to shift left with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/overflowing-rsh-1.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/overflowing-rsh-1.rs:LL:CC:
 attempt to shift right with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/overflowing-rsh-2.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/overflowing-rsh-2.rs:LL:CC:
 attempt to shift right with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/panic1.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/panic1.rs:LL:CC:
 panicking from libstd
 stack backtrace:

tests/panic/panic2.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/panic2.rs:LL:CC:
 42-panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/panic3.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/panic3.rs:LL:CC:
 panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/panic4.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/panic4.rs:LL:CC:
 42-panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/panic/transmute_fat2.stderr

@@ -1,3 +1,4 @@
+
 thread 'main' panicked at tests/panic/transmute_fat2.rs:LL:CC:
 index out of bounds: the len is 0 but the index is 0
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/pass/panic/catch_panic.stderr

@@ -1,35 +1,46 @@
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from std::panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 Caught panic message (&str): Hello from std::panic
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from std::panic: 1
 Caught panic message (String): Hello from std::panic: 1
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from std::panic_any: 2
 Caught panic message (String): Hello from std::panic_any: 2
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Box<dyn Any>
 Failed to get caught panic message.
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from core::panic
 Caught panic message (&str): Hello from core::panic
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 Hello from core::panic: 5
 Caught panic message (String): Hello from core::panic: 5
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 index out of bounds: the len is 3 but the index is 4
 Caught panic message (String): index out of bounds: the len is 3 but the index is 4
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 attempt to divide by zero
 Caught panic message (&str): attempt to divide by zero
+
 thread 'main' panicked at RUSTLIB/core/src/ptr/const_ptr.rs:LL:CC:
 align_offset: align is not a power-of-two
 Caught panic message (&str): align_offset: align is not a power-of-two
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 assertion failed: false
 Caught panic message (&str): assertion failed: false
+
 thread 'main' panicked at tests/pass/panic/catch_panic.rs:LL:CC:
 assertion failed: false
 Caught panic message (&str): assertion failed: false

tests/pass/panic/concurrent-panic.stderr

@@ -1,12 +1,14 @@
 Thread 1 starting, will block on mutex
 Thread 1 reported it has started
+
 thread '<unnamed>' panicked at tests/pass/panic/concurrent-panic.rs:LL:CC:
 panic in thread 2
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 Thread 2 blocking on thread 1
 Thread 2 reported it has started
 Unlocking mutex
+
 thread '<unnamed>' panicked at tests/pass/panic/concurrent-panic.rs:LL:CC:
 panic in thread 1
 Thread 1 has exited

tests/pass/panic/nested_panic_caught.stderr

@@ -1,7 +1,9 @@
+
 thread 'main' panicked at tests/pass/panic/nested_panic_caught.rs:LL:CC:
 once
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'main' panicked at tests/pass/panic/nested_panic_caught.rs:LL:CC:
 twice
 stack backtrace:

tests/pass/panic/thread_panic.stderr

@@ -1,6 +1,8 @@
+
 thread '<unnamed>' panicked at tests/pass/panic/thread_panic.rs:LL:CC:
 Hello!
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
+
 thread 'childthread' panicked at tests/pass/panic/thread_panic.rs:LL:CC:
 Hello, world!