Auto merge of #93691 - compiler-errors:mir-tainted-by-errors, r=oli-obk

Implement `tainted_by_errors` in MIR borrowck, use it to skip CTFE

Putting this up for initial review. The issue that I found is when we're evaluating a const, we're doing borrowck, but doing nothing with the fact that borrowck fails.

This implements a `tainted_by_errors` field for MIR borrowck like we have in infcx, so we can use that information to return an `Err` during const eval if our const fails to borrowck.

This PR needs some cleaning up. I should probably just use `Result` in more places, instead of `.expect`ing in the places I am, but I just wanted it to compile so I could see if it worked!

Fixes #93646

r? `@oli-obk`
feel free to reassign

compiler/rustc_borrowck/src/borrowck_errors.rs

@@ -327,7 +327,7 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         verb: &str,
         optional_adverb_for_moved: &str,
         moved_path: Option<String>,
-    ) -> DiagnosticBuilder<'cx> {
+    ) -> DiagnosticBuilder<'tcx> {
         let moved_path = moved_path.map(|mp| format!(": `{}`", mp)).unwrap_or_default();
 
         struct_span_err!(

compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -55,7 +55,7 @@ impl<'tcx> UniverseInfo<'tcx> {
                     found,
                     TypeError::RegionsPlaceholderMismatch,
                 );
-                err.buffer(&mut mbcx.errors_buffer);
+                mbcx.buffer_error(err);
             }
             UniverseInfoInner::TypeOp(ref type_op_info) => {
                 type_op_info.report_error(mbcx, placeholder, error_element, cause);
@@ -64,11 +64,9 @@ impl<'tcx> UniverseInfo<'tcx> {
                 // FIXME: This error message isn't great, but it doesn't show
                 // up in the existing UI tests. Consider investigating this
                 // some more.
-                mbcx.infcx
-                    .tcx
-                    .sess
-                    .struct_span_err(cause.span, "higher-ranked subtype error")
-                    .buffer(&mut mbcx.errors_buffer);
+                mbcx.buffer_error(
+                    mbcx.infcx.tcx.sess.struct_span_err(cause.span, "higher-ranked subtype error"),
+                );
             }
         }
     }
@@ -149,7 +147,7 @@ trait TypeOpInfo<'tcx> {
         {
             adjusted
         } else {
-            self.fallback_error(tcx, cause.span).buffer(&mut mbcx.errors_buffer);
+            mbcx.buffer_error(self.fallback_error(tcx, cause.span));
             return;
         };
 
@@ -178,9 +176,9 @@ trait TypeOpInfo<'tcx> {
         let nice_error = self.nice_error(tcx, cause, placeholder_region, error_region);
 
         if let Some(nice_error) = nice_error {
-            nice_error.buffer(&mut mbcx.errors_buffer);
+            mbcx.buffer_error(nice_error);
         } else {
-            self.fallback_error(tcx, span).buffer(&mut mbcx.errors_buffer);
+            mbcx.buffer_error(self.fallback_error(tcx, span));
         }
     }
 }

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -104,9 +104,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
             );
 
-            err.buffer(&mut self.errors_buffer);
+            self.buffer_error(err);
         } else {
-            if let Some((reported_place, _)) = self.move_error_reported.get(&move_out_indices) {
+            if let Some((reported_place, _)) = self.has_move_error(&move_out_indices) {
                 if self.prefixes(*reported_place, PrefixSet::All).any(|p| p == used_place) {
                     debug!(
                         "report_use_of_moved_or_uninitialized place: error suppressed \
@@ -449,12 +449,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
             }
 
-            if let Some((_, mut old_err)) =
-                self.move_error_reported.insert(move_out_indices, (used_place, err))
-            {
-                // Cancel the old error so it doesn't ICE.
-                old_err.cancel();
-            }
+            self.buffer_move_error(move_out_indices, (used_place, err));
         }
     }
 
@@ -503,7 +498,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 Some(borrow_span),
                 None,
             );
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     pub(crate) fn report_use_while_mutably_borrowed(
@@ -1021,7 +1016,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         if self.body.local_decls[borrowed_local].is_ref_to_thread_local() {
             let err =
                 self.report_thread_local_value_does_not_live_long_enough(drop_span, borrow_span);
-            err.buffer(&mut self.errors_buffer);
+            self.buffer_error(err);
             return;
         }
 
@@ -1113,7 +1108,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             ),
         };
 
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     fn report_local_value_does_not_live_long_enough(
@@ -1295,7 +1290,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             None,
         );
 
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     fn report_thread_local_value_does_not_live_long_enough(
@@ -1810,7 +1805,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     loan.kind.describe_mutability(),
                 );
 
-                err.buffer(&mut self.errors_buffer);
+                self.buffer_error(err);
 
                 return;
             }
@@ -1836,7 +1831,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
 
         self.explain_deref_coercion(loan, &mut err);
 
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     fn explain_deref_coercion(&mut self, loan: &BorrowData<'tcx>, err: &mut DiagnosticBuilder<'_>) {
@@ -1938,7 +1933,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             }
         }
         err.span_label(span, msg);
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     fn classify_drop_access_kind(&self, place: PlaceRef<'tcx>) -> StorageDeadOrDrop<'tcx> {

compiler/rustc_borrowck/src/diagnostics/move_errors.rs

@@ -264,7 +264,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         };
 
         self.add_move_hints(error, &mut err, err_span);
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     fn report_cannot_move_from_static(

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -626,7 +626,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             }
         }
 
-        err.buffer(&mut self.errors_buffer);
+        self.buffer_error(err);
     }
 
     /// User cannot make signature of a trait mutable without changing the

compiler/rustc_borrowck/src/diagnostics/outlives_suggestion.rs

@@ -256,6 +256,6 @@ impl OutlivesSuggestionBuilder {
         diag.sort_span = mir_span.shrink_to_hi();
 
         // Buffer the diagnostic
-        diag.buffer(&mut mbcx.errors_buffer);
+        mbcx.buffer_error(diag);
     }
 }

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -168,14 +168,12 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     let type_test_span = type_test.locations.span(&self.body);
 
                     if let Some(lower_bound_region) = lower_bound_region {
-                        self.infcx
-                            .construct_generic_bound_failure(
-                                type_test_span,
-                                None,
-                                type_test.generic_kind,
-                                lower_bound_region,
-                            )
-                            .buffer(&mut self.errors_buffer);
+                        self.buffer_error(self.infcx.construct_generic_bound_failure(
+                            type_test_span,
+                            None,
+                            type_test.generic_kind,
+                            lower_bound_region,
+                        ));
                     } else {
                         // FIXME. We should handle this case better. It
                         // indicates that we have e.g., some region variable
@@ -186,27 +184,22 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         // to report it; we could probably handle it by
                         // iterating over the universal regions and reporting
                         // an error that multiple bounds are required.
-                        self.infcx
-                            .tcx
-                            .sess
-                            .struct_span_err(
-                                type_test_span,
-                                &format!("`{}` does not live long enough", type_test.generic_kind),
-                            )
-                            .buffer(&mut self.errors_buffer);
+                        self.buffer_error(self.infcx.tcx.sess.struct_span_err(
+                            type_test_span,
+                            &format!("`{}` does not live long enough", type_test.generic_kind),
+                        ));
                     }
                 }
 
                 RegionErrorKind::UnexpectedHiddenRegion { span, hidden_ty, member_region } => {
                     let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty);
                     let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region);
-                    unexpected_hidden_region_diagnostic(
+                    self.buffer_error(unexpected_hidden_region_diagnostic(
                         self.infcx.tcx,
                         span,
                         named_ty,
                         named_region,
-                    )
-                    .buffer(&mut self.errors_buffer);
+                    ));
                 }
 
                 RegionErrorKind::BoundUniversalRegionError {
@@ -285,7 +278,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         if let (Some(f), Some(o)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) {
             let nice = NiceRegionError::new_from_span(self.infcx, cause.span, o, f);
             if let Some(diag) = nice.try_report_from_nll() {
-                diag.buffer(&mut self.errors_buffer);
+                self.buffer_error(diag);
                 return;
             }
         }
@@ -375,7 +368,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             }
         }
 
-        diag.buffer(&mut self.errors_buffer);
+        self.buffer_error(diag);
     }
 
     /// Report a specialized error when `FnMut` closures return a reference to a captured variable.