Auto merge of #115045 - RalfJung:unwind-terminate-reason, r=davidtwco

when terminating during unwinding, show the reason why

With this, the output on double-panic becomes something like that:
```
thread 'main' panicked at src/tools/miri/tests/fail/panic/double_panic.rs:15:5:
first
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at src/tools/miri/tests/fail/panic/double_panic.rs:10:9:
second
stack backtrace:
   0:           0xbe273a - std::backtrace_rs::backtrace::miri::trace_unsynchronized::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
                               at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:99:5
   1:           0xbe22e6 - std::backtrace_rs::backtrace::miri::trace::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
                               at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:62:14
   2:           0xbe1086 - std::backtrace_rs::backtrace::trace_unsynchronized::<[closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
                               at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   3:           0xba3afd - std::sys_common::backtrace::_print_fmt
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:67:5
   4:           0xba2471 - <std::sys_common::backtrace::_print::DisplayBacktrace as std::fmt::Display>::fmt
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:44:22
   5:           0xbcf754 - core::fmt::rt::Argument::<'_>::fmt
                               at /home/r/src/rust/rustc.3/library/core/src/fmt/rt.rs:138:9
   6:           0x9b8f81 - std::fmt::write
                               at /home/r/src/rust/rustc.3/library/core/src/fmt/mod.rs:1094:17
   7:           0x21391d - <std::sys::unix::stdio::Stderr as std::io::Write>::write_fmt
                               at /home/r/src/rust/rustc.3/library/std/src/io/mod.rs:1714:15
   8:           0xba37b1 - std::sys_common::backtrace::_print
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:47:5
   9:           0xba365b - std::sys_common::backtrace::print
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:34:9
  10:           0x143c67 - std::panic_hook_with_disk_dump::{closure#1}
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:278:22
  11:           0x144187 - std::panic_hook_with_disk_dump
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:312:9
  12:           0x143659 - std::panicking::default_hook
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:239:5
  13:           0x1482a7 - std::panicking::rust_panic_with_hook
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:729:13
  14:           0x1475d5 - std::rt::begin_panic::<&str>::{closure#0}
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:650:9
  15:           0xba496a - std::sys_common::backtrace::__rust_end_short_backtrace::<[closure@std::rt::begin_panic<&str>::{closure#0}], !>
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:170:18
  16:           0x147599 - std::rt::begin_panic::<&str>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:649:12
  17:            0x31916 - <Foo as std::ops::Drop>::drop
                               at src/tools/miri/tests/fail/panic/double_panic.rs:10:9
  18:           0x1a2b5e - std::ptr::drop_in_place::<Foo> - shim(Some(Foo))
                               at /home/r/src/rust/rustc.3/library/core/src/ptr/mod.rs:497:1
  19:            0x202bf - main
                               at src/tools/miri/tests/fail/panic/double_panic.rs:16:1
  20:            0xcc6a8 - <fn() as std::ops::FnOnce<()>>::call_once - shim(fn())
                               at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:250:5
  21:           0xba47d9 - std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:154:18
  22:           0x141a6a - std::rt::lang_start::<()>::{closure#0}
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:166:18
  23:            0xcca18 - std::ops::function::impls::<impl std::ops::FnOnce<()> for &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>::call_once
                               at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:284:13
  24:           0x146469 - std::panicking::try::do_call::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
  25:           0x145e09 - std::panicking::try::<i32, &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
  26:            0x7b0ac - std::panic::catch_unwind::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
                               at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
  27:           0x14189b - std::rt::lang_start_internal::{closure#2}
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:48
  28:           0x146481 - std::panicking::try::do_call::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
  29:           0x145e2c - std::panicking::try::<isize, [closure@std::rt::lang_start_internal::{closure#2}]>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
  30:            0x7b0d5 - std::panic::catch_unwind::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
                               at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
  31:           0x1418b0 - std::rt::lang_start_internal
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:20
  32:           0x141a97 - std::rt::lang_start::<()>
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:165:17
thread 'main' panicked at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:126:5:
panic in a destructor during cleanup
stack backtrace:
   0:           0xe9f6d7 - std::backtrace_rs::backtrace::miri::trace_unsynchronized::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
                               at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:99:5
   1:           0xe9f27d - std::backtrace_rs::backtrace::miri::trace::<&mut [closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
                               at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/miri.rs:62:14
   2:           0xe9e016 - std::backtrace_rs::backtrace::trace_unsynchronized::<[closure@std::sys_common::backtrace::_print_fmt::{closure#1}]>
                               at /home/r/src/rust/rustc.3/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   3:           0xba3afd - std::sys_common::backtrace::_print_fmt
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:67:5
   4:           0xba2471 - <std::sys_common::backtrace::_print::DisplayBacktrace as std::fmt::Display>::fmt
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:44:22
   5:           0xbcf754 - core::fmt::rt::Argument::<'_>::fmt
                               at /home/r/src/rust/rustc.3/library/core/src/fmt/rt.rs:138:9
   6:           0x9b8f81 - std::fmt::write
                               at /home/r/src/rust/rustc.3/library/core/src/fmt/mod.rs:1094:17
   7:           0x4d0895 - <std::sys::unix::stdio::Stderr as std::io::Write>::write_fmt
                               at /home/r/src/rust/rustc.3/library/std/src/io/mod.rs:1714:15
   8:           0xba37b1 - std::sys_common::backtrace::_print
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:47:5
   9:           0xba365b - std::sys_common::backtrace::print
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:34:9
  10:           0x400bd4 - std::panic_hook_with_disk_dump::{closure#1}
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:278:22
  11:           0x144187 - std::panic_hook_with_disk_dump
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:312:9
  12:           0x143659 - std::panicking::default_hook
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:239:5
  13:           0x1482a7 - std::panicking::rust_panic_with_hook
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:729:13
  14:           0x40403b - std::panicking::begin_panic_handler::{closure#0}
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:619:13
  15:           0xe618b3 - std::sys_common::backtrace::__rust_end_short_backtrace::<[closure@std::panicking::begin_panic_handler::{closure#0}], !>
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:170:18
  16:           0x403fc8 - std::panicking::begin_panic_handler
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:617:5
  17:           0xee23e9 - core::panicking::panic_nounwind_fmt
                               at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:96:14
  18:           0xee29e6 - core::panicking::panic_nounwind
                               at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:126:5
  19:           0xee365e - core::panicking::panic_in_cleanup
                               at /home/r/src/rust/rustc.3/library/core/src/panicking.rs:206:5
  20:            0x2028a - main
                               at src/tools/miri/tests/fail/panic/double_panic.rs:13:1
  21:           0x3895ee - <fn() as std::ops::FnOnce<()>>::call_once - shim(fn())
                               at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:250:5
  22:           0xe61725 - std::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
                               at /home/r/src/rust/rustc.3/library/std/src/sys_common/backtrace.rs:154:18
  23:           0x3fe9aa - std::rt::lang_start::<()>::{closure#0}
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:166:18
  24:           0x389962 - std::ops::function::impls::<impl std::ops::FnOnce<()> for &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>::call_once
                               at /home/r/src/rust/rustc.3/library/core/src/ops/function.rs:284:13
  25:           0x4033b9 - std::panicking::try::do_call::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
  26:           0x402d58 - std::panicking::try::<i32, &dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
  27:           0x337ff7 - std::panic::catch_unwind::<&dyn std::ops::Fn() -> i32 + std::marker::Sync + std::panic::RefUnwindSafe, i32>
                               at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
  28:           0x3fe7e7 - std::rt::lang_start_internal::{closure#2}
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:48
  29:           0x4033d6 - std::panicking::try::do_call::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:524:40
  30:           0x402d7f - std::panicking::try::<isize, [closure@std::rt::lang_start_internal::{closure#2}]>
                               at /home/r/src/rust/rustc.3/library/std/src/panicking.rs:488:19
  31:           0x338028 - std::panic::catch_unwind::<[closure@std::rt::lang_start_internal::{closure#2}], isize>
                               at /home/r/src/rust/rustc.3/library/std/src/panic.rs:142:14
  32:           0x1418b0 - std::rt::lang_start_internal
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:148:20
  33:           0x3fe9dc - std::rt::lang_start::<()>
                               at /home/r/src/rust/rustc.3/library/std/src/rt.rs:165:17
thread caused non-unwinding panic. aborting.
```
If we also land https://github.com/rust-lang/rust/pull/115020, the 2nd backtrace disappears, hopefully making the "panic in a destructor during cleanup" easier to see.

Fixes https://github.com/rust-lang/rust/issues/114954.

6 files changed, 30 insertions, 13 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index 61d3de5c405..90848dbfbc7 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -756,6 +756,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ///
     /// If `target` is `UnwindAction::Unreachable`, that indicates the function does not allow
     /// unwinding, and doing so is UB.
+    #[cold] // usually we have normal returns, not unwinding
     pub fn unwind_to_block(&mut self, target: mir::UnwindAction) -> InterpResult<'tcx> {
         self.frame_mut().loc = match target {
             mir::UnwindAction::Cleanup(block) => Left(mir::Location { block, statement_index: 0 }),
@@ -763,9 +764,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             mir::UnwindAction::Unreachable => {
                 throw_ub_custom!(fluent::const_eval_unreachable_unwind);
             }
-            mir::UnwindAction::Terminate => {
+            mir::UnwindAction::Terminate(reason) => {
                 self.frame_mut().loc = Right(self.frame_mut().body.span);
-                M::unwind_terminate(self)?;
+                M::unwind_terminate(self, reason)?;
                 // This might have pushed a new stack frame, or it terminated execution.
                 // Either way, `loc` will not be updated.
                 return Ok(());
diff --git a/compiler/rustc_const_eval/src/interpret/machine.rs b/compiler/rustc_const_eval/src/interpret/machine.rs
index d3c73b896c0..6be2e406917 100644
--- a/compiler/rustc_const_eval/src/interpret/machine.rs
+++ b/compiler/rustc_const_eval/src/interpret/machine.rs
@@ -222,7 +222,10 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
     fn panic_nounwind(_ecx: &mut InterpCx<'mir, 'tcx, Self>, msg: &str) -> InterpResult<'tcx>;
 
     /// Called when unwinding reached a state where execution should be terminated.
-    fn unwind_terminate(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx>;
+    fn unwind_terminate(
+        ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        reason: mir::UnwindTerminateReason,
+    ) -> InterpResult<'tcx>;
 
     /// Called for all binary operations where the LHS has pointer type.
     ///
@@ -462,6 +465,7 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
 
     /// Called immediately after a stack frame got popped, but before jumping back to the caller.
     /// The `locals` have already been destroyed!
+    #[inline(always)]
     fn after_stack_pop(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         _frame: Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>,
@@ -501,7 +505,10 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     }
 
     #[inline(always)]
-    fn unwind_terminate(_ecx: &mut InterpCx<$mir, $tcx, Self>) -> InterpResult<$tcx> {
+    fn unwind_terminate(
+        _ecx: &mut InterpCx<$mir, $tcx, Self>,
+        _reason: mir::UnwindTerminateReason,
+    ) -> InterpResult<$tcx> {
         unreachable!("unwinding cannot happen during compile-time evaluation")
     }
 
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs
index b2ebcceceb3..ca7c484ea31 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -196,8 +196,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 }
             }
 
-            UnwindTerminate => {
-                M::unwind_terminate(self)?;
+            UnwindTerminate(reason) => {
+                M::unwind_terminate(self, reason)?;
             }
 
             // When we encounter Resume, we've finished unwinding
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index e67098a3ac3..f288ddc25d3 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -1037,7 +1037,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 self.check_op(ops::Generator(hir::GeneratorKind::Gen))
             }
 
-            TerminatorKind::UnwindTerminate => {
+            TerminatorKind::UnwindTerminate(_) => {
                 // Cleanup blocks are skipped for const checking (see `visit_basic_block_data`).
                 span_bug!(self.span, "`Terminate` terminator outside of cleanup block")
             }
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs b/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
index a8c61d2c8fd..fd6bc2ee9af 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/post_drop_elaboration.rs
@@ -106,7 +106,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
                 }
             }
 
-            mir::TerminatorKind::UnwindTerminate
+            mir::TerminatorKind::UnwindTerminate(_)
             | mir::TerminatorKind::Call { .. }
             | mir::TerminatorKind::Assert { .. }
             | mir::TerminatorKind::FalseEdge { .. }
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 0dfbbf73dce..b829f24ab7a 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -10,8 +10,8 @@ use rustc_middle::mir::{
     traversal, BasicBlock, BinOp, Body, BorrowKind, CastKind, CopyNonOverlapping, Local, Location,
     MirPass, MirPhase, NonDivergingIntrinsic, NullOp, Operand, Place, PlaceElem, PlaceRef,
     ProjectionElem, RetagKind, RuntimePhase, Rvalue, SourceScope, Statement, StatementKind,
-    Terminator, TerminatorKind, UnOp, UnwindAction, VarDebugInfo, VarDebugInfoContents,
-    START_BLOCK,
+    Terminator, TerminatorKind, UnOp, UnwindAction, UnwindTerminateReason, VarDebugInfo,
+    VarDebugInfoContents, START_BLOCK,
 };
 use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeVisitableExt};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
@@ -274,7 +274,16 @@ impl<'a, 'tcx> CfgChecker<'a, 'tcx> {
                     self.fail(location, "`UnwindAction::Continue` in no-unwind function");
                 }
             }
-            UnwindAction::Unreachable | UnwindAction::Terminate => (),
+            UnwindAction::Terminate(UnwindTerminateReason::InCleanup) => {
+                if !is_cleanup {
+                    self.fail(
+                        location,
+                        "`UnwindAction::Terminate(InCleanup)` in a non-cleanup block",
+                    );
+                }
+            }
+            // These are allowed everywhere.
+            UnwindAction::Unreachable | UnwindAction::Terminate(UnwindTerminateReason::Abi) => (),
         }
     }
 }
@@ -501,7 +510,7 @@ impl<'a, 'tcx> Visitor<'tcx> for CfgChecker<'a, 'tcx> {
                     self.fail(location, "Cannot `UnwindResume` in a function that cannot unwind")
                 }
             }
-            TerminatorKind::UnwindTerminate => {
+            TerminatorKind::UnwindTerminate(_) => {
                 let bb = location.block;
                 if !self.body.basic_blocks[bb].is_cleanup {
                     self.fail(location, "Cannot `UnwindTerminate` from non-cleanup basic block")
@@ -1233,7 +1242,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
             | TerminatorKind::InlineAsm { .. }
             | TerminatorKind::GeneratorDrop
             | TerminatorKind::UnwindResume
-            | TerminatorKind::UnwindTerminate
+            | TerminatorKind::UnwindTerminate(_)
             | TerminatorKind::Return
             | TerminatorKind::Unreachable => {}
         }