Rollup merge of #115272 - RalfJung:miri-error-print, r=saethlin

miri/diagnostics: don't forget to print_backtrace when ICEing on unexpected errors

This should fix the missing output encountered [here](https://github.com/rust-lang/rust/issues/115145#issuecomment-1694334410).

r? `@saethlin`

1 files changed, 27 insertions, 38 deletions

diff --git a/src/tools/miri/src/diagnostics.rs b/src/tools/miri/src/diagnostics.rs
index f3285ccf917..799a9a8e4be 100644
--- a/src/tools/miri/src/diagnostics.rs
+++ b/src/tools/miri/src/diagnostics.rs
@@ -1,9 +1,8 @@
-use std::fmt;
+use std::fmt::{self, Write};
 use std::num::NonZeroU64;
 
 use log::trace;
 
-use rustc_const_eval::ReportErrorExt;
 use rustc_errors::DiagnosticMessage;
 use rustc_span::{source_map::DUMMY_SP, SpanData, Symbol};
 use rustc_target::abi::{Align, Size};
@@ -271,10 +270,13 @@ pub fn report_error<'tcx, 'mir>(
         };
         (title, helps)
     } else {
-        #[rustfmt::skip]
         let title = match e.kind() {
-            UndefinedBehavior(UndefinedBehaviorInfo::ValidationError(e)) if matches!(e.kind, ValidationErrorKind::PointerAsInt { .. } | ValidationErrorKind::PartialPointer) =>
-                bug!("This validation error should be impossible in Miri: {:?}", e.kind),
+            UndefinedBehavior(UndefinedBehaviorInfo::ValidationError(validation_err))
+                if matches!(validation_err.kind, ValidationErrorKind::PointerAsInt { .. } | ValidationErrorKind::PartialPointer) =>
+            {
+                ecx.handle_ice(); // print interpreter backtrace
+                bug!("This validation error should be impossible in Miri: {}", ecx.format_error(e));
+            }
             UndefinedBehavior(_) =>
                 "Undefined Behavior",
             ResourceExhaustion(_) =>
@@ -290,8 +292,10 @@ pub fn report_error<'tcx, 'mir>(
                 InvalidProgramInfo::Layout(..)
             ) =>
                 "post-monomorphization error",
-            kind =>
-                bug!("This error should be impossible in Miri: {kind:?}"),
+            _ => {
+                ecx.handle_ice(); // print interpreter backtrace
+                bug!("This error should be impossible in Miri: {}", ecx.format_error(e));
+            }
         };
         #[rustfmt::skip]
         let helps = match e.kind() {
@@ -333,30 +337,22 @@ pub fn report_error<'tcx, 'mir>(
 
     let stacktrace = ecx.generate_stacktrace();
     let (stacktrace, was_pruned) = prune_stacktrace(stacktrace, &ecx.machine);
-    let (e, backtrace) = e.into_parts();
-    backtrace.print_backtrace();
-
-    // We want to dump the allocation if this is `InvalidUninitBytes`. Since `add_args` consumes
-    // the `InterpError`, we extract the variables it before that.
-    let extra = match e {
-        UndefinedBehavior(UndefinedBehaviorInfo::InvalidUninitBytes(Some((alloc_id, access)))) =>
-            Some((alloc_id, access)),
-        _ => None,
-    };
 
-    // FIXME(fee1-dead), HACK: we want to use the error as title therefore we can just extract the
-    // label and arguments from the InterpError.
-    let e = {
-        let handler = &ecx.tcx.sess.parse_sess.span_diagnostic;
-        let mut diag = ecx.tcx.sess.struct_allow("");
-        let msg = e.diagnostic_message();
-        e.add_args(handler, &mut diag);
-        let s = handler.eagerly_translate_to_string(msg, diag.args());
-        diag.cancel();
-        s
-    };
+    // We want to dump the allocation if this is `InvalidUninitBytes`. Since `format_error` consumes `e`, we compute the outut early.
+    let mut extra = String::new();
+    match e.kind() {
+        UndefinedBehavior(UndefinedBehaviorInfo::InvalidUninitBytes(Some((alloc_id, access)))) => {
+            writeln!(
+                extra,
+                "Uninitialized memory occurred at {alloc_id:?}{range:?}, in this allocation:",
+                range = access.bad,
+            ).unwrap();
+            writeln!(extra, "{:?}", ecx.dump_alloc(*alloc_id)).unwrap();
+        }
+        _ => {}
+    }
 
-    msg.insert(0, e);
+    msg.insert(0, ecx.format_error(e));
 
     report_msg(
         DiagLevel::Error,
@@ -375,6 +371,8 @@ pub fn report_error<'tcx, 'mir>(
         );
     }
 
+    eprint!("{extra}"); // newlines are already in the string
+
     // Debug-dump all locals.
     for (i, frame) in ecx.active_thread_stack().iter().enumerate() {
         trace!("-------------------");
@@ -385,15 +383,6 @@ pub fn report_error<'tcx, 'mir>(
         }
     }
 
-    // Extra output to help debug specific issues.
-    if let Some((alloc_id, access)) = extra {
-        eprintln!(
-            "Uninitialized memory occurred at {alloc_id:?}{range:?}, in this allocation:",
-            range = access.bad,
-        );
-        eprintln!("{:?}", ecx.dump_alloc(alloc_id));
-    }
-
     None
 }