Rollup merge of #106321 - compiler-errors:delayed-bug-backtrace, r=Nilstrieb

Collect and emit proper backtraces for `delay_span_bug`s

This is a follow-up to #106317, which addresses this comment (https://github.com/rust-lang/rust/issues/106267#issuecomment-1367507507) which notes that `delay_span_bug`s' backtraces are nonsense.

Captures and emits the backtrace of the delayed span bug when it's *created*, rather than using the backtrace of the place where delayed bugs are flushed.

---

To test, I delayed a span bug during HIR typeck, specifically in `typeck_with_fallback`...

Before, note `flush_delayed` on frame 18. This is at the end of the compilation session, far from where the bug is being delayed.

```
error: internal compiler error: test
 --> /home/ubuntu/test.rs:1:1
  |
1 | fn main() {}
  | ^^^^^^^^^
  |
  = note: delayed at compiler/rustc_hir_typeck/src/lib.rs:196:14

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1634:13
stack backtrace:
   0:     0x7f9c3ec69dd1 - std::backtrace_rs::backtrace::libunwind::trace::h26056f81198c6594
                               at /home/ubuntu/rust2/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f9c3ec69dd1 - std::backtrace_rs::backtrace::trace_unsynchronized::hacfb345a0c6d5bb1
                               at /home/ubuntu/rust2/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f9c3ec69dd1 - std::sys_common::backtrace::_print_fmt::h18ea6016ac8030f3
                               at /home/ubuntu/rust2/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f9c3ec69dd1 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::he35dde201d0c2d09
                               at /home/ubuntu/rust2/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f9c3ecee308 - core::fmt::write::h094ad263467a053c
                               at /home/ubuntu/rust2/library/core/src/fmt/mod.rs:1208:17
   5:     0x7f9c3ec8aaf1 - std::io::Write::write_fmt::hd47b4e2324b4d9b7
                               at /home/ubuntu/rust2/library/std/src/io/mod.rs:1682:15
   6:     0x7f9c3ec69bfa - std::sys_common::backtrace::_print::h43044162653a17fc
                               at /home/ubuntu/rust2/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f9c3ec69bfa - std::sys_common::backtrace::print::hc8605da258fa5aeb
                               at /home/ubuntu/rust2/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f9c3ec4db87 - std::panicking::default_hook::{{closure}}::h9e37f23f75122a15
   9:     0x7f9c3ec4d97b - std::panicking::default_hook::h602873a063f84da2
                               at /home/ubuntu/rust2/library/std/src/panicking.rs:286:9
  10:     0x7f9c3f6672b2 - <alloc[48d7b30605060536]::boxed::Box<dyn for<'a, 'b> core[672e3947e150d6c6]::ops::function::Fn<(&'a core[672e3947e150d6c6]::panic::panic_info::PanicInfo<'b>,), Output = ()> + core[672e3947e150d6c6]::marker::Send + core[672e3947e150d6c6]::marker::Sync> as core[672e3947e150d6c6]::ops::function::Fn<(&core[672e3947e150d6c6]::panic::panic_info::PanicInfo,)>>::call
                               at /home/ubuntu/rust2/library/alloc/src/boxed.rs:2002:9
  11:     0x7f9c3f6672b2 - rustc_driver[f5b6d32d8905ecdd]::DEFAULT_HOOK::{closure#0}::{closure#0}
                               at /home/ubuntu/rust2/compiler/rustc_driver/src/lib.rs:1204:17
  12:     0x7f9c3ec4e0d3 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hfd13333ca953ae8e
                               at /home/ubuntu/rust2/library/alloc/src/boxed.rs:2002:9
  13:     0x7f9c3ec4e0d3 - std::panicking::rust_panic_with_hook::h45753e10264ebe7e
                               at /home/ubuntu/rust2/library/std/src/panicking.rs:692:13
  14:     0x7f9c422a1aa3 - std[3330b4673efabfce]::panicking::begin_panic::<rustc_errors[1b15f4e7e49d1fd5]::ExplicitBug>::{closure#0}
                               at /home/ubuntu/rust2/library/std/src/panicking.rs:608:9
  15:     0x7f9c422a1a46 - std[3330b4673efabfce]::sys_common::backtrace::__rust_end_short_backtrace::<std[3330b4673efabfce]::panicking::begin_panic<rustc_errors[1b15f4e7e49d1fd5]::ExplicitBug>::{closure#0}, !>
                               at /home/ubuntu/rust2/library/std/src/sys_common/backtrace.rs:137:18
  16:     0x7f9c3f63a996 - std[3330b4673efabfce]::panicking::begin_panic::<rustc_errors[1b15f4e7e49d1fd5]::ExplicitBug>
                               at /home/ubuntu/rust2/library/std/src/panicking.rs:607:12
  17:     0x7f9c4227a496 - std[3330b4673efabfce]::panic::panic_any::<rustc_errors[1b15f4e7e49d1fd5]::ExplicitBug>
                               at /home/ubuntu/rust2/library/std/src/panic.rs:61:5
  18:     0x7f9c4227cdf7 - <rustc_errors[1b15f4e7e49d1fd5]::HandlerInner>::flush_delayed::<alloc[48d7b30605060536]::vec::Vec<rustc_errors[1b15f4e7e49d1fd5]::diagnostic::Diagnostic>, &str, rustc_errors[1b15f4e7e49d1fd5]::ExplicitBug>
                               at /home/ubuntu/rust2/compiler/rustc_errors/src/lib.rs:1634:13
  19:     0x7f9c422498cf - <rustc_errors[1b15f4e7e49d1fd5]::Handler>::flush_delayed
                               at /home/ubuntu/rust2/compiler/rustc_errors/src/lib.rs:1225:9

[ FRAMES INTENTIONALLY OMITTED ]

  44:     0x7f9c3f6f3584 - <std[3330b4673efabfce]::thread::Builder>::spawn_unchecked_::<rustc_interface[947706ead88047d0]::util::run_in_thread_pool_with_globals<rustc_interface[947706ead88047d0]::interface::run_compiler<core[672e3947e150d6c6]::result::Result<(), rustc_errors[1b15f4e7e49d1fd5]::ErrorGuaranteed>, rustc_driver[f5b6d32d8905ecdd]::run_compiler::{closure#1}>::{closure#0}, core[672e3947e150d6c6]::result::Result<(), rustc_errors[1b15f4e7e49d1fd5]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[672e3947e150d6c6]::result::Result<(), rustc_errors[1b15f4e7e49d1fd5]::ErrorGuaranteed>>::{closure#1}
                               at /home/ubuntu/rust2/library/std/src/thread/mod.rs:549:30
  45:     0x7f9c3f6f3584 - <<std[3330b4673efabfce]::thread::Builder>::spawn_unchecked_<rustc_interface[947706ead88047d0]::util::run_in_thread_pool_with_globals<rustc_interface[947706ead88047d0]::interface::run_compiler<core[672e3947e150d6c6]::result::Result<(), rustc_errors[1b15f4e7e49d1fd5]::ErrorGuaranteed>, rustc_driver[f5b6d32d8905ecdd]::run_compiler::{closure#1}>::{closure#0}, core[672e3947e150d6c6]::result::Result<(), rustc_errors[1b15f4e7e49d1fd5]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[672e3947e150d6c6]::result::Result<(), rustc_errors[1b15f4e7e49d1fd5]::ErrorGuaranteed>>::{closure#1} as core[672e3947e150d6c6]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
                               at /home/ubuntu/rust2/library/core/src/ops/function.rs:250:5
  46:     0x7f9c3ec81968 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::he8b26fc22c6f51ec
                               at /home/ubuntu/rust2/library/alloc/src/boxed.rs:1988:9
  47:     0x7f9c3ec81968 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h5cf9cbe75a8c3ddc
                               at /home/ubuntu/rust2/library/alloc/src/boxed.rs:1988:9
  48:     0x7f9c3ec5f99c - std::sys::unix::thread::Thread::new::thread_start::h2d6dd4455e97d031
                               at /home/ubuntu/rust2/library/std/src/sys/unix/thread.rs:108:17
  49:     0x7f9c37c69609 - start_thread
  50:     0x7f9c3ead0133 - clone
  51:                0x0 - <unknown>
```

After, note `typeck_with_fallback` on the 5th frame, that's where we *actually* need to be pointed to:

```
error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: test
 --> /home/ubuntu/test.rs:1:1
  |
1 | fn main() {}
  | ^^^^^^^^^
  |
  = note: delayed at    0: <rustc_errors::HandlerInner>::emit_diagnostic
                       at ./compiler/rustc_errors/src/lib.rs:1279:29
             1: <rustc_errors::HandlerInner>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
                       at ./compiler/rustc_errors/src/lib.rs:1553:9
             2: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
                       at ./compiler/rustc_errors/src/lib.rs:995:9
             3: <rustc_session::session::Session>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
                       at ./compiler/rustc_session/src/session.rs:600:9
             4: rustc_hir_typeck::typeck_with_fallback::<rustc_hir_typeck::typeck::{closure#0}>::{closure#0}
                       at ./compiler/rustc_hir_typeck/src/lib.rs:196:5
             5: rustc_hir_typeck::typeck_with_fallback::<rustc_hir_typeck::typeck::{closure#0}>
                       at ./compiler/rustc_hir_typeck/src/lib.rs:185:36
             6: rustc_hir_typeck::typeck
                       at ./compiler/rustc_hir_typeck/src/lib.rs:166:9

[ FRAMES INTENTIONALLY OMITTED ]

           108: std::panicking::try::<core::result::Result<(), rustc_errors::ErrorGuaranteed>, core::panic::unwind_safe::AssertUnwindSafe<<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#1}::{closure#0}>>
                       at ./library/std/src/panicking.rs:447:19
           109: std::panic::catch_unwind::<core::panic::unwind_safe::AssertUnwindSafe<<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#1}::{closure#0}>, core::result::Result<(), rustc_errors::ErrorGuaranteed>>
                       at ./library/std/src/panic.rs:140:14
           110: <std::thread::Builder>::spawn_unchecked_::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#1}
                       at ./library/std/src/thread/mod.rs:549:30
           111: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorGuaranteed>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
                       at ./library/core/src/ops/function.rs:250:5
           112: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at ./library/alloc/src/boxed.rs:1988:9
           113: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at ./library/alloc/src/boxed.rs:1988:9
           114: std::sys::unix::thread::Thread::new::thread_start
                       at ./library/std/src/sys/unix/thread.rs:108:17
           115: start_thread
           116: clone
```

1 files changed, 15 insertions, 23 deletions

diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index b4d23e96f8f..66e5c41f56c 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -40,7 +40,6 @@ use rustc_span::source_map::SourceMap;
 use rustc_span::HashStableContext;
 use rustc_span::{Loc, Span};
 
-use std::any::Any;
 use std::borrow::Cow;
 use std::fmt;
 use std::hash::Hash;
@@ -364,9 +363,9 @@ pub use rustc_span::fatal_error::{FatalError, FatalErrorMarker};
 /// or `.span_bug` rather than a failed assertion, etc.
 pub struct ExplicitBug;
 
-/// Signifies that the compiler died with an explicit call to `.delay_good_path_bug`
+/// Signifies that the compiler died with an explicit call to `.delay_*_bug`
 /// rather than a failed assertion, etc.
-pub struct GoodPathBug;
+pub struct DelayedBugPanic;
 
 pub use diagnostic::{
     AddToDiagnostic, DecorateLint, Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId,
@@ -399,7 +398,7 @@ struct HandlerInner {
     warn_count: usize,
     deduplicated_err_count: usize,
     emitter: Box<dyn Emitter + sync::Send>,
-    delayed_span_bugs: Vec<Diagnostic>,
+    delayed_span_bugs: Vec<DelayedDiagnostic>,
     delayed_good_path_bugs: Vec<DelayedDiagnostic>,
     /// This flag indicates that an expected diagnostic was emitted and suppressed.
     /// This is used for the `delayed_good_path_bugs` check.
@@ -505,11 +504,7 @@ impl Drop for HandlerInner {
 
         if !self.has_errors() {
             let bugs = std::mem::replace(&mut self.delayed_span_bugs, Vec::new());
-            self.flush_delayed(
-                bugs,
-                "no errors encountered even though `delay_span_bug` issued",
-                ExplicitBug,
-            );
+            self.flush_delayed(bugs, "no errors encountered even though `delay_span_bug` issued");
         }
 
         // FIXME(eddyb) this explains what `delayed_good_path_bugs` are!
@@ -520,9 +515,8 @@ impl Drop for HandlerInner {
         if !self.has_any_message() && !self.suppressed_expected_diag {
             let bugs = std::mem::replace(&mut self.delayed_good_path_bugs, Vec::new());
             self.flush_delayed(
-                bugs.into_iter().map(DelayedDiagnostic::decorate),
+                bugs,
                 "no warnings or errors encountered even though `delayed_good_path_bugs` issued",
-                GoodPathBug,
             );
         }
 
@@ -1223,11 +1217,7 @@ impl Handler {
     pub fn flush_delayed(&self) {
         let mut inner = self.inner.lock();
         let bugs = std::mem::replace(&mut inner.delayed_span_bugs, Vec::new());
-        inner.flush_delayed(
-            bugs,
-            "no errors encountered even though `delay_span_bug` issued",
-            ExplicitBug,
-        );
+        inner.flush_delayed(bugs, "no errors encountered even though `delay_span_bug` issued");
     }
 }
 
@@ -1287,7 +1277,9 @@ impl HandlerInner {
             // once *any* errors were emitted (and truncate `delayed_span_bugs`
             // when an error is first emitted, also), but maybe there's a case
             // in which that's not sound? otherwise this is really inefficient.
-            self.delayed_span_bugs.push(diagnostic.clone());
+            let backtrace = std::backtrace::Backtrace::force_capture();
+            self.delayed_span_bugs
+                .push(DelayedDiagnostic::with_backtrace(diagnostic.clone(), backtrace));
 
             if !self.flags.report_delayed_bugs {
                 return Some(ErrorGuaranteed::unchecked_claim_error_was_emitted());
@@ -1562,7 +1554,6 @@ impl HandlerInner {
         }
         let mut diagnostic = Diagnostic::new(Level::DelayedBug, msg);
         diagnostic.set_span(sp.into());
-        diagnostic.note(&format!("delayed at {}", std::panic::Location::caller()));
         self.emit_diagnostic(&mut diagnostic).unwrap()
     }
 
@@ -1605,12 +1596,13 @@ impl HandlerInner {
 
     fn flush_delayed(
         &mut self,
-        bugs: impl IntoIterator<Item = Diagnostic>,
+        bugs: impl IntoIterator<Item = DelayedDiagnostic>,
         explanation: impl Into<DiagnosticMessage> + Copy,
-        panic_with: impl Any + Send + 'static,
     ) {
         let mut no_bugs = true;
-        for mut bug in bugs {
+        for bug in bugs {
+            let mut bug = bug.decorate();
+
             if no_bugs {
                 // Put the overall explanation before the `DelayedBug`s, to
                 // frame them better (e.g. separate warnings from them).
@@ -1633,9 +1625,9 @@ impl HandlerInner {
             self.emit_diagnostic(&mut bug);
         }
 
-        // Panic with `ExplicitBug` to avoid "unexpected panic" messages.
+        // Panic with `DelayedBugPanic` to avoid "unexpected panic" messages.
         if !no_bugs {
-            panic::panic_any(panic_with);
+            panic::panic_any(DelayedBugPanic);
         }
     }