defer opaque type errors, generally greatly reduce tainting

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -51,7 +51,7 @@ mod conflict_errors;
 mod explain_borrow;
 mod move_errors;
 mod mutability_errors;
-mod opaque_suggestions;
+mod opaque_types;
 mod region_errors;
 
 pub(crate) use bound_region_errors::{ToUniverseInfo, UniverseInfo};

compiler/rustc_borrowck/src/diagnostics/opaque_suggestions.rs → compiler/rustc_borrowck/src/diagnostics/opaque_types.rs

@@ -18,9 +18,28 @@ use rustc_trait_selection::errors::impl_trait_overcapture_suggestion;
 use crate::MirBorrowckCtxt;
 use crate::borrow_set::BorrowData;
 use crate::consumers::RegionInferenceContext;
+use crate::region_infer::opaque_types::DeferredOpaqueTypeError;
 use crate::type_check::Locations;
 
 impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
+    pub(crate) fn report_opaque_type_errors(&mut self, errors: Vec<DeferredOpaqueTypeError<'tcx>>) {
+        if errors.is_empty() {
+            return;
+        }
+        let mut guar = None;
+        for error in errors {
+            guar = Some(match error {
+                DeferredOpaqueTypeError::InvalidOpaqueTypeArgs(err) => err.report(self.infcx),
+                DeferredOpaqueTypeError::LifetimeMismatchOpaqueParam(err) => {
+                    self.infcx.dcx().emit_err(err)
+                }
+            });
+        }
+        let guar = guar.unwrap();
+        self.root_cx.set_tainted_by_errors(guar);
+        self.infcx.set_tainted_by_errors(guar);
+    }
+
     /// Try to note when an opaque is involved in a borrowck error and that
     /// opaque captures lifetimes due to edition 2024.
     // FIXME: This code is otherwise somewhat general, and could easily be adapted

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -92,9 +92,6 @@ impl<'tcx> RegionErrors<'tcx> {
     ) -> impl Iterator<Item = (RegionErrorKind<'tcx>, ErrorGuaranteed)> {
         self.0.into_iter()
     }
-    pub(crate) fn has_errors(&self) -> Option<ErrorGuaranteed> {
-        self.0.get(0).map(|x| x.1)
-    }
 }
 
 impl std::fmt::Debug for RegionErrors<'_> {

compiler/rustc_borrowck/src/handle_placeholders.rs

@@ -216,22 +216,11 @@ pub(crate) fn compute_sccs_applying_placeholder_outlives_constraints<'tcx>(
         placeholder_index_to_region: _,
         liveness_constraints,
         mut outlives_constraints,
-        mut member_constraints,
+        member_constraints,
         universe_causes,
         type_tests,
     } = constraints;
 
-    if let Some(guar) = universal_regions.tainted_by_errors() {
-        debug!("Universal regions tainted by errors; removing constraints!");
-        // Suppress unhelpful extra errors in `infer_opaque_types` by clearing out all
-        // outlives bounds that we may end up checking.
-        outlives_constraints = Default::default();
-        member_constraints = Default::default();
-
-        // Also taint the entire scope.
-        infcx.set_tainted_by_errors(guar);
-    }
-
     let fr_static = universal_regions.fr_static;
     let compute_sccs =
         |constraints: &OutlivesConstraintSet<'tcx>,

compiler/rustc_borrowck/src/lib.rs

@@ -375,7 +375,7 @@ fn do_mir_borrowck<'tcx>(
         polonius_context,
     );
 
-    regioncx.infer_opaque_types(root_cx, &infcx, opaque_type_values);
+    let opaque_type_errors = regioncx.infer_opaque_types(root_cx, &infcx, opaque_type_values);
 
     // Dump MIR results into a file, if that is enabled. This lets us
     // write unit-tests, as well as helping with debugging.
@@ -471,7 +471,11 @@ fn do_mir_borrowck<'tcx>(
     };
 
     // Compute and report region errors, if any.
-    mbcx.report_region_errors(nll_errors);
+    if nll_errors.is_empty() {
+        mbcx.report_opaque_type_errors(opaque_type_errors);
+    } else {
+        mbcx.report_region_errors(nll_errors);
+    }
 
     let (mut flow_analysis, flow_entry_states) =
         get_flow_results(tcx, body, &move_data, &borrow_set, &regioncx);

compiler/rustc_borrowck/src/nll.rs

@@ -148,11 +148,6 @@ pub(crate) fn compute_regions<'tcx>(
     let (closure_region_requirements, nll_errors) =
         regioncx.solve(infcx, body, polonius_output.clone());
 
-    if let Some(guar) = nll_errors.has_errors() {
-        // Suppress unhelpful extra errors in `infer_opaque_types`.
-        infcx.set_tainted_by_errors(guar);
-    }
-
     NllOutput {
         regioncx,
         polonius_input: polonius_facts.map(Box::new),

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -44,7 +44,7 @@ use crate::{
 
 mod dump_mir;
 mod graphviz;
-mod opaque_types;
+pub(crate) mod opaque_types;
 mod reverse_sccs;
 
 pub(crate) mod values;

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -6,14 +6,21 @@ use rustc_middle::ty::{
     TypeVisitableExt, fold_regions,
 };
 use rustc_span::Span;
-use rustc_trait_selection::opaque_types::check_opaque_type_parameter_valid;
+use rustc_trait_selection::opaque_types::{
+    InvalidOpaqueTypeArgs, check_opaque_type_parameter_valid,
+};
 use tracing::{debug, instrument};
 
 use super::RegionInferenceContext;
 use crate::BorrowCheckRootCtxt;
 use crate::session_diagnostics::LifetimeMismatchOpaqueParam;
 use crate::universal_regions::RegionClassification;
 
+pub(crate) enum DeferredOpaqueTypeError<'tcx> {
+    InvalidOpaqueTypeArgs(InvalidOpaqueTypeArgs<'tcx>),
+    LifetimeMismatchOpaqueParam(LifetimeMismatchOpaqueParam<'tcx>),
+}
+
 impl<'tcx> RegionInferenceContext<'tcx> {
     /// Resolve any opaque types that were encountered while borrow checking
     /// this item. This is then used to get the type in the `type_of` query.
@@ -58,13 +65,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ///
     /// [rustc-dev-guide chapter]:
     /// https://rustc-dev-guide.rust-lang.org/opaque-types-region-infer-restrictions.html
-    #[instrument(level = "debug", skip(self, root_cx, infcx), ret)]
+    #[instrument(level = "debug", skip(self, root_cx, infcx))]
     pub(crate) fn infer_opaque_types(
         &self,
         root_cx: &mut BorrowCheckRootCtxt<'tcx>,
         infcx: &InferCtxt<'tcx>,
         opaque_ty_decls: FxIndexMap<OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>>,
-    ) {
+    ) -> Vec<DeferredOpaqueTypeError<'tcx>> {
+        let mut errors = Vec::new();
         let mut decls_modulo_regions: FxIndexMap<OpaqueTypeKey<'tcx>, (OpaqueTypeKey<'tcx>, Span)> =
             FxIndexMap::default();
 
@@ -124,8 +132,15 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             });
             debug!(?concrete_type);
 
-            let ty =
-                infcx.infer_opaque_definition_from_instantiation(opaque_type_key, concrete_type);
+            let ty = match infcx
+                .infer_opaque_definition_from_instantiation(opaque_type_key, concrete_type)
+            {
+                Ok(ty) => ty,
+                Err(err) => {
+                    errors.push(DeferredOpaqueTypeError::InvalidOpaqueTypeArgs(err));
+                    continue;
+                }
+            };
 
             // Sometimes, when the hidden type is an inference variable, it can happen that
             // the hidden type becomes the opaque type itself. In this case, this was an opaque
@@ -149,25 +164,27 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             // non-region parameters. This is necessary because within the new solver we perform
             // various query operations modulo regions, and thus could unsoundly select some impls
             // that don't hold.
-            if !ty.references_error()
-                && let Some((prev_decl_key, prev_span)) = decls_modulo_regions.insert(
-                    infcx.tcx.erase_regions(opaque_type_key),
-                    (opaque_type_key, concrete_type.span),
-                )
-                && let Some((arg1, arg2)) = std::iter::zip(
-                    prev_decl_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
-                    opaque_type_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
-                )
-                .find(|(arg1, arg2)| arg1 != arg2)
+            if let Some((prev_decl_key, prev_span)) = decls_modulo_regions.insert(
+                infcx.tcx.erase_regions(opaque_type_key),
+                (opaque_type_key, concrete_type.span),
+            ) && let Some((arg1, arg2)) = std::iter::zip(
+                prev_decl_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
+                opaque_type_key.iter_captured_args(infcx.tcx).map(|(_, arg)| arg),
+            )
+            .find(|(arg1, arg2)| arg1 != arg2)
             {
-                infcx.dcx().emit_err(LifetimeMismatchOpaqueParam {
-                    arg: arg1,
-                    prev: arg2,
-                    span: prev_span,
-                    prev_span: concrete_type.span,
-                });
+                errors.push(DeferredOpaqueTypeError::LifetimeMismatchOpaqueParam(
+                    LifetimeMismatchOpaqueParam {
+                        arg: arg1,
+                        prev: arg2,
+                        span: prev_span,
+                        prev_span: concrete_type.span,
+                    },
+                ));
             }
         }
+
+        errors
     }
 
     /// Map the regions in the type to named regions. This is similar to what
@@ -260,19 +277,13 @@ impl<'tcx> InferCtxt<'tcx> {
         &self,
         opaque_type_key: OpaqueTypeKey<'tcx>,
         instantiated_ty: OpaqueHiddenType<'tcx>,
-    ) -> Ty<'tcx> {
-        if let Some(e) = self.tainted_by_errors() {
-            return Ty::new_error(self.tcx, e);
-        }
-
-        if let Err(err) = check_opaque_type_parameter_valid(
+    ) -> Result<Ty<'tcx>, InvalidOpaqueTypeArgs<'tcx>> {
+        check_opaque_type_parameter_valid(
             self,
             opaque_type_key,
             instantiated_ty.span,
             DefiningScopeKind::MirBorrowck,
-        ) {
-            return Ty::new_error(self.tcx, err.report(self));
-        }
+        )?;
 
         let definition_ty = instantiated_ty
             .remap_generic_params_to_declaration_params(
@@ -282,10 +293,7 @@ impl<'tcx> InferCtxt<'tcx> {
             )
             .ty;
 
-        if let Err(e) = definition_ty.error_reported() {
-            return Ty::new_error(self.tcx, e);
-        }
-
-        definition_ty
+        definition_ty.error_reported()?;
+        Ok(definition_ty)
     }
 }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -182,6 +182,17 @@ pub(crate) fn type_check<'tcx>(
         )
     });
 
+    // In case type check encountered an error region, we suppress unhelpful extra
+    // errors in by clearing out all outlives bounds that we may end up checking.
+    if let Some(guar) = universal_region_relations.universal_regions.encountered_re_error() {
+        debug!("encountered an error region; removing constraints!");
+        constraints.outlives_constraints = Default::default();
+        constraints.member_constraints = Default::default();
+        constraints.type_tests = Default::default();
+        root_cx.set_tainted_by_errors(guar);
+        infcx.set_tainted_by_errors(guar);
+    }
+
     MirTypeckResults {
         constraints,
         universal_region_relations,

compiler/rustc_borrowck/src/universal_regions.rs

@@ -217,7 +217,7 @@ struct UniversalRegionIndices<'tcx> {
 
     /// Whether we've encountered an error region. If we have, cancel all
     /// outlives errors, as they are likely bogus.
-    pub tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
+    pub encountered_re_error: Cell<Option<ErrorGuaranteed>>,
 }
 
 #[derive(Debug, PartialEq)]
@@ -442,8 +442,8 @@ impl<'tcx> UniversalRegions<'tcx> {
         self.fr_fn_body
     }
 
-    pub(crate) fn tainted_by_errors(&self) -> Option<ErrorGuaranteed> {
-        self.indices.tainted_by_errors.get()
+    pub(crate) fn encountered_re_error(&self) -> Option<ErrorGuaranteed> {
+        self.indices.encountered_re_error.get()
     }
 }
 
@@ -706,7 +706,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
         UniversalRegionIndices {
             indices: global_mapping.chain(arg_mapping).collect(),
             fr_static,
-            tainted_by_errors: Cell::new(None),
+            encountered_re_error: Cell::new(None),
         }
     }
 
@@ -916,7 +916,7 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
         match r.kind() {
             ty::ReVar(..) => r.as_var(),
             ty::ReError(guar) => {
-                self.tainted_by_errors.set(Some(guar));
+                self.encountered_re_error.set(Some(guar));
                 // We use the `'static` `RegionVid` because `ReError` doesn't actually exist in the
                 // `UniversalRegionIndices`. This is fine because 1) it is a fallback only used if
                 // errors are being emitted and 2) it leaves the happy path unaffected.

tests/ui/impl-trait/issues/type-error-post-normalization-test.rs

@@ -0,0 +1,24 @@
+//@ compile-flags: -Zvalidate-mir -Zinline-mir=yes
+
+// This previously introduced a `{type_error}`` in the MIR body
+// during the `PostAnalysisNormalize` pass. While the underlying issue
+// #135528 did not get fixed, this reproducer no longer ICEs.
+
+#![feature(type_alias_impl_trait)]
+type Tait = impl Copy;
+
+fn set(x: &isize) -> isize {
+    *x
+}
+
+#[define_opaque(Tait)]
+fn d(x: Tait) {
+    set(x);
+}
+
+#[define_opaque(Tait)]
+fn other_define() -> Tait {
+    () //~^ ERROR concrete type differs from previous defining opaque type use
+}
+
+fn main() {}

tests/ui/impl-trait/issues/type-error-post-normalization-test.stderr

@@ -0,0 +1,14 @@
+error: concrete type differs from previous defining opaque type use
+  --> $DIR/type-error-post-normalization-test.rs:20:22
+   |
+LL | fn other_define() -> Tait {
+   |                      ^^^^ expected `&isize`, got `()`
+   |
+note: previous use here
+  --> $DIR/type-error-post-normalization-test.rs:16:9
+   |
+LL |     set(x);
+   |         ^
+
+error: aborting due to 1 previous error
+

tests/ui/rfcs/type-alias-impl-trait/higher-ranked-regions-basic.rs

@@ -41,6 +41,7 @@ mod capture_tait_complex_pass {
     #[define_opaque(Opq2)]
     fn test() -> Opq2 {}
     //~^ ERROR: expected generic lifetime parameter, found `'a`
+    //~| ERROR: expected generic lifetime parameter, found `'b`
 }
 
 // Same as the above, but make sure that different placeholder regions are not equal.
@@ -80,6 +81,7 @@ mod constrain_pass {
     #[define_opaque(Opq2)]
     fn test() -> Opq2 {}
     //~^ ERROR: expected generic lifetime parameter, found `'a`
+    //~| ERROR: expected generic lifetime parameter, found `'a`
 }
 
 fn main() {}