attempt to clarify what the backtrace belongs to when there could be ambiguity

Author: RalfJung

src/tools/miri/src/diagnostics.rs

@@ -362,23 +362,26 @@ fn report_msg<'tcx>(
     }
 
     // Show note and help messages.
+    let mut extra_span = false;
     for (span_data, note) in &notes {
         if let Some(span_data) = span_data {
             err.span_note(span_data.span(), note);
+            extra_span = true;
         } else {
             err.note(note);
         }
     }
     for (span_data, help) in &helps {
         if let Some(span_data) = span_data {
             err.span_help(span_data.span(), help);
+            extra_span = true;
         } else {
             err.help(help);
         }
     }
     if notes.len() + helps.len() > 0 {
         // Add visual separator before backtrace.
-        err.note("BACKTRACE:");
+        err.note(if extra_span { "BACKTRACE (of the first span):" } else { "BACKTRACE:" });
     }
     // Add backtrace
     for (idx, frame_info) in stacktrace.iter().enumerate() {

src/tools/miri/tests/fail/box-cell-alias.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x1] by a Unique retag
    |
 LL |     let res = helper(val, ptr);
    |                      ^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `helper` at $DIR/box-cell-alias.rs:LL:CC
 note: inside `main`
   --> $DIR/box-cell-alias.rs:LL:CC

src/tools/miri/tests/fail/data_race/alloc_read_race.stderr

@@ -11,7 +11,7 @@ LL |             pointer.store(Box::into_raw(Box::new_uninit()), Ordering::Relax
    |                                         ^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/alloc_read_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/alloc_write_race.stderr

@@ -11,7 +11,7 @@ LL |                 .store(Box::into_raw(Box::<usize>::new_uninit()) as *mut us
    |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/alloc_write_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/atomic_read_na_write_race1.stderr

@@ -11,7 +11,7 @@ LL |             *(c.0 as *mut usize) = 32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/atomic_read_na_write_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/atomic_read_na_write_race2.stderr

@@ -11,7 +11,7 @@ LL |             atomic_ref.load(Ordering::SeqCst)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/atomic_read_na_write_race2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/atomic_write_na_read_race1.stderr

@@ -11,7 +11,7 @@ LL |             atomic_ref.store(32, Ordering::SeqCst)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/atomic_write_na_read_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/atomic_write_na_read_race2.stderr

@@ -11,7 +11,7 @@ LL |             let _val = *(c.0 as *mut usize);
    |                        ^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/atomic_write_na_read_race2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/atomic_write_na_write_race1.stderr

@@ -11,7 +11,7 @@ LL |             *(c.0 as *mut usize) = 32;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/atomic_write_na_write_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/atomic_write_na_write_race2.stderr

@@ -11,7 +11,7 @@ LL |             atomic_ref.store(64, Ordering::SeqCst);
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/atomic_write_na_write_race2.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/dangling_thread_async_race.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/dangling_thread_async_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/dangling_thread_race.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/dangling_thread_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/dealloc_read_race1.stderr

@@ -16,7 +16,7 @@ LL |             let _val = *ptr.0;
    |                        ^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/dealloc_read_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/dealloc_read_race_stack.stderr

@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/dealloc_read_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/dealloc_write_race1.stderr

@@ -16,7 +16,7 @@ LL |             *ptr.0 = 2;
    |             ^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/dealloc_write_race1.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/dealloc_write_race_stack.stderr

@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire) = 3;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/dealloc_write_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/enable_after_join_to_main.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/enable_after_join_to_main.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/fence_after_load.stderr

@@ -11,7 +11,7 @@ LL |         unsafe { V = 1 }
    |                  ^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/fence_after_load.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/read_write_race.stderr

@@ -11,7 +11,7 @@ LL |             let _val = *c.0;
    |                        ^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/read_write_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/read_write_race_stack.stderr

@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire) = 3;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/read_write_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/relax_acquire_race.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/relax_acquire_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/release_seq_race.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/release_seq_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/release_seq_race_same_thread.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/release_seq_race_same_thread.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/rmw_race.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 1;
    |             ^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/rmw_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/stack_pop_race.stderr

@@ -11,7 +11,7 @@ LL |         let _val = unsafe { *ptr.0 };
    |                             ^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `race` at $DIR/stack_pop_race.rs:LL:CC
 note: inside `main`
   --> $DIR/stack_pop_race.rs:LL:CC

src/tools/miri/tests/fail/data_race/write_write_race.stderr

@@ -11,7 +11,7 @@ LL |             *c.0 = 32;
    |             ^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/write_write_race.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/data_race/write_write_race_stack.stderr

@@ -11,7 +11,7 @@ LL |             *pointer.load(Ordering::Acquire) = 3;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside closure at $DIR/write_write_race_stack.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/function_calls/exported_symbol_clashing.stderr

@@ -14,7 +14,7 @@ help: then it's defined here again, in crate `exported_symbol_clashing`
    |
 LL | fn bar() {}
    | ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/exported_symbol_clashing.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/function_calls/exported_symbol_shim_clashing.stderr

@@ -12,7 +12,7 @@ LL | |
 LL | |     unreachable!()
 LL | | }
    | |_^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/exported_symbol_shim_clashing.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/stacked_borrows/alias_through_mutation.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     *target = 13;
    |     ^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/alias_through_mutation.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/stacked_borrows/aliasing_mut1.stderr

@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | pub fn safe(_x: &mut i32, _y: &mut i32) {}
    |             ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut1.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut1.rs:LL:CC

src/tools/miri/tests/fail/stacked_borrows/aliasing_mut2.stderr

@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | pub fn safe(_x: &i32, _y: &mut i32) {}
    |             ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut2.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut2.rs:LL:CC

src/tools/miri/tests/fail/stacked_borrows/aliasing_mut3.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique FnEntry reta
    |
 LL |     safe_raw(xraw, xshr);
    |     ^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut3.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut3.rs:LL:CC

src/tools/miri/tests/fail/stacked_borrows/aliasing_mut4.stderr

@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | pub fn safe(_x: &i32, _y: &mut Cell<i32>) {}
    |             ^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `safe` at $DIR/aliasing_mut4.rs:LL:CC
 note: inside `main`
   --> $DIR/aliasing_mut4.rs:LL:CC

src/tools/miri/tests/fail/stacked_borrows/box_exclusive_violation1.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |     *our = 5;
    |     ^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `unknown_code_2` at $DIR/box_exclusive_violation1.rs:LL:CC
 note: inside `demo_box_advanced_unique`
   --> $DIR/box_exclusive_violation1.rs:LL:CC

src/tools/miri/tests/fail/stacked_borrows/box_noalias_violation.stderr

@@ -16,7 +16,7 @@ help: <TAG> is this argument
    |
 LL | unsafe fn test(mut x: Box<i32>, y: *const i32) -> i32 {
    |                ^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `test` at $DIR/box_noalias_violation.rs:LL:CC
 note: inside `main`
   --> $DIR/box_noalias_violation.rs:LL:CC

src/tools/miri/tests/fail/stacked_borrows/buggy_as_mut_slice.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0xc] by a Unique retag
    |
 LL |         unsafe { from_raw_parts_mut(self_.as_ptr() as *mut T, self_.len()) }
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/buggy_as_mut_slice.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/stacked_borrows/buggy_split_at_mut.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x10] by a Unique retag
    |
 LL |                 from_raw_parts_mut(ptr.offset(mid as isize), len - mid),
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/buggy_split_at_mut.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/stacked_borrows/disable_mut_does_not_merge_srw.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
    |
 LL |         *base = 1;
    |         ^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/disable_mut_does_not_merge_srw.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

src/tools/miri/tests/fail/stacked_borrows/fnentry_invalidation.stderr

@@ -19,7 +19,7 @@ help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique FnEntry reta
    |
 LL |     x.do_bad();
    |     ^^^^^^^^^^
-   = note: BACKTRACE:
+   = note: BACKTRACE (of the first span):
    = note: inside `main` at $DIR/fnentry_invalidation.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace