Avoid a span_delayed_bug in compute_regions.

By storing error guarantees in `RegionErrors`.

Author: nnethercote

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -1,7 +1,7 @@
 //! Error reporting machinery for lifetime errors.
 
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_errors::{Applicability, DiagnosticBuilder, MultiSpan};
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def::Res::Def;
 use rustc_hir::def_id::DefId;
@@ -73,7 +73,7 @@ impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> {
 ///
 /// Usually we expect this to either be empty or contain a small number of items, so we can avoid
 /// allocation most of the time.
-pub(crate) struct RegionErrors<'tcx>(Vec<RegionErrorKind<'tcx>>, TyCtxt<'tcx>);
+pub(crate) struct RegionErrors<'tcx>(Vec<(RegionErrorKind<'tcx>, ErrorGuaranteed)>, TyCtxt<'tcx>);
 
 impl<'tcx> RegionErrors<'tcx> {
     pub fn new(tcx: TyCtxt<'tcx>) -> Self {
@@ -82,15 +82,18 @@ impl<'tcx> RegionErrors<'tcx> {
     #[track_caller]
     pub fn push(&mut self, val: impl Into<RegionErrorKind<'tcx>>) {
         let val = val.into();
-        self.1.sess.dcx().delayed_bug(format!("{val:?}"));
-        self.0.push(val);
+        let guar = self.1.sess.dcx().delayed_bug(format!("{val:?}"));
+        self.0.push((val, guar));
     }
     pub fn is_empty(&self) -> bool {
         self.0.is_empty()
     }
-    pub fn into_iter(self) -> impl Iterator<Item = RegionErrorKind<'tcx>> {
+    pub fn into_iter(self) -> impl Iterator<Item = (RegionErrorKind<'tcx>, ErrorGuaranteed)> {
         self.0.into_iter()
     }
+    pub fn has_errors(&self) -> Option<ErrorGuaranteed> {
+        self.0.get(0).map(|x| x.1)
+    }
 }
 
 impl std::fmt::Debug for RegionErrors<'_> {
@@ -304,10 +307,11 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         let mut last_unexpected_hidden_region: Option<(Span, Ty<'_>, ty::OpaqueTypeKey<'tcx>)> =
             None;
 
-        for nll_error in nll_errors.into_iter() {
+        for (nll_error, _) in nll_errors.into_iter() {
             match nll_error {
                 RegionErrorKind::TypeTestError { type_test } => {
-                    // Try to convert the lower-bound region into something named we can print for the user.
+                    // Try to convert the lower-bound region into something named we can print for
+                    // the user.
                     let lower_bound_region = self.to_error_region(type_test.lower_bound);
 
                     let type_test_span = type_test.span;

compiler/rustc_borrowck/src/nll.rs

@@ -184,12 +184,9 @@ pub(crate) fn compute_regions<'cx, 'tcx>(
     let (closure_region_requirements, nll_errors) =
         regioncx.solve(infcx, body, polonius_output.clone());
 
-    if !nll_errors.is_empty() {
+    if let Some(guar) = nll_errors.has_errors() {
         // Suppress unhelpful extra errors in `infer_opaque_types`.
-        infcx.set_tainted_by_errors(infcx.dcx().span_delayed_bug(
-            body.span,
-            "`compute_regions` tainted `infcx` with errors but did not emit any errors",
-        ));
+        infcx.set_tainted_by_errors(guar);
     }
 
     let remapped_opaque_tys = regioncx.infer_opaque_types(infcx, opaque_type_values);