overflow errors: change source to a concrete enum

compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -1,4 +1,4 @@
-use crate::traits::error_reporting::TypeErrCtxtExt;
+use crate::traits::error_reporting::{OverflowCause, TypeErrCtxtExt};
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
 use crate::traits::{needs_normalization, BoundVarReplacer, PlaceholderReplacer};
 use rustc_data_structures::stack::ensure_sufficient_stack;
@@ -60,8 +60,12 @@ impl<'tcx> NormalizationFolder<'_, 'tcx> {
         let tcx = infcx.tcx;
         let recursion_limit = tcx.recursion_limit();
         if !recursion_limit.value_within_limit(self.depth) {
+            let ty::Alias(_, data) = *alias_ty.kind() else {
+                unreachable!();
+            };
+
             self.at.infcx.err_ctxt().report_overflow_error(
-                &alias_ty,
+                OverflowCause::DeeplyNormalize(data),
                 self.at.cause.span,
                 true,
                 |_| {},
@@ -118,7 +122,7 @@ impl<'tcx> NormalizationFolder<'_, 'tcx> {
         let recursion_limit = tcx.recursion_limit();
         if !recursion_limit.value_within_limit(self.depth) {
             self.at.infcx.err_ctxt().report_overflow_error(
-                &ty::Const::new_unevaluated(tcx, uv, ty),
+                OverflowCause::DeeplyNormalize(ty::AliasTy::new(tcx, uv.def, uv.args)),
                 self.at.cause.span,
                 true,
                 |_| {},

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -55,25 +55,26 @@ use super::{
 
 pub use rustc_infer::traits::error_reporting::*;
 
+pub enum OverflowCause<'tcx> {
+    DeeplyNormalize(ty::AliasTy<'tcx>),
+    TraitSolver(ty::Predicate<'tcx>),
+}
+
 pub trait TypeErrCtxtExt<'tcx> {
-    fn build_overflow_error<T>(
+    fn build_overflow_error(
         &self,
-        predicate: &T,
+        cause: OverflowCause<'tcx>,
         span: Span,
         suggest_increasing_limit: bool,
-    ) -> DiagnosticBuilder<'tcx>
-    where
-        T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>;
+    ) -> DiagnosticBuilder<'tcx>;
 
-    fn report_overflow_error<T>(
+    fn report_overflow_error(
         &self,
-        predicate: &T,
+        cause: OverflowCause<'tcx>,
         span: Span,
         suggest_increasing_limit: bool,
         mutate: impl FnOnce(&mut Diagnostic),
-    ) -> !
-    where
-        T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>;
+    ) -> !;
 
     fn report_overflow_no_abort(&self, obligation: PredicateObligation<'tcx>) -> ErrorGuaranteed;
 
@@ -241,17 +242,14 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     /// whose result could not be truly determined and thus we can't say
     /// if the program type checks or not -- and they are unusual
     /// occurrences in any case.
-    fn report_overflow_error<T>(
+    fn report_overflow_error(
         &self,
-        predicate: &T,
+        cause: OverflowCause<'tcx>,
         span: Span,
         suggest_increasing_limit: bool,
         mutate: impl FnOnce(&mut Diagnostic),
-    ) -> !
-    where
-        T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>,
-    {
-        let mut err = self.build_overflow_error(predicate, span, suggest_increasing_limit);
+    ) -> ! {
+        let mut err = self.build_overflow_error(cause, span, suggest_increasing_limit);
         mutate(&mut err);
         err.emit();
 
@@ -264,33 +262,52 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         );
     }
 
-    fn build_overflow_error<T>(
+    fn build_overflow_error(
         &self,
-        predicate: &T,
+        cause: OverflowCause<'tcx>,
         span: Span,
         suggest_increasing_limit: bool,
-    ) -> DiagnosticBuilder<'tcx>
-    where
-        T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>,
-    {
-        let predicate = self.resolve_vars_if_possible(predicate.clone());
-        let mut pred_str = predicate.to_string();
-
-        if pred_str.len() > 50 {
-            // We don't need to save the type to a file, we will be talking about this type already
-            // in a separate note when we explain the obligation, so it will be available that way.
-            let mut cx: FmtPrinter<'_, '_> =
-                FmtPrinter::new_with_limit(self.tcx, Namespace::TypeNS, rustc_session::Limit(6));
-            predicate.print(&mut cx).unwrap();
-            pred_str = cx.into_buffer();
+    ) -> DiagnosticBuilder<'tcx> {
+        fn with_short_path<'tcx, T>(tcx: TyCtxt<'tcx>, value: T) -> String
+        where
+            T: fmt::Display + Print<'tcx, FmtPrinter<'tcx, 'tcx>>,
+        {
+            let s = value.to_string();
+            if s.len() > 50 {
+                // We don't need to save the type to a file, we will be talking about this type already
+                // in a separate note when we explain the obligation, so it will be available that way.
+                let mut cx: FmtPrinter<'_, '_> =
+                    FmtPrinter::new_with_limit(tcx, Namespace::TypeNS, rustc_session::Limit(6));
+                value.print(&mut cx).unwrap();
+                cx.into_buffer()
+            } else {
+                s
+            }
         }
-        let mut err = struct_span_code_err!(
-            self.dcx(),
-            span,
-            E0275,
-            "overflow evaluating the requirement `{}`",
-            pred_str,
-        );
+
+        let mut err = match cause {
+            OverflowCause::DeeplyNormalize(alias_ty) => {
+                let alias_ty = self.resolve_vars_if_possible(alias_ty);
+                let kind = alias_ty.opt_kind(self.tcx).map_or("alias", |k| k.descr());
+                let alias_str = with_short_path(self.tcx, alias_ty);
+                struct_span_code_err!(
+                    self.dcx(),
+                    span,
+                    E0275,
+                    "overflow normalizing the {kind} `{alias_str}`",
+                )
+            }
+            OverflowCause::TraitSolver(predicate) => {
+                let predicate = self.resolve_vars_if_possible(predicate);
+                let pred_str = with_short_path(self.tcx, predicate);
+                struct_span_code_err!(
+                    self.dcx(),
+                    span,
+                    E0275,
+                    "overflow evaluating the requirement `{pred_str}`",
+                )
+            }
+        };
 
         if suggest_increasing_limit {
             self.suggest_new_overflow_limit(&mut err);
@@ -316,7 +333,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let predicate = obligation.predicate.clone().to_predicate(self.tcx);
         let predicate = self.resolve_vars_if_possible(predicate);
         self.report_overflow_error(
-            &predicate,
+            OverflowCause::TraitSolver(predicate),
             obligation.cause.span,
             suggest_increasing_limit,
             |err| {
@@ -367,7 +384,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
     fn report_overflow_no_abort(&self, obligation: PredicateObligation<'tcx>) -> ErrorGuaranteed {
         let obligation = self.resolve_vars_if_possible(obligation);
-        let mut err = self.build_overflow_error(&obligation.predicate, obligation.cause.span, true);
+        let mut err = self.build_overflow_error(
+            OverflowCause::TraitSolver(obligation.predicate),
+            obligation.cause.span,
+            true,
+        );
         self.note_obligation_cause(&mut err, &obligation);
         self.point_at_returns_when_relevant(&mut err, &obligation);
         err.emit()

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -435,12 +435,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     .recursion_limit()
                     .value_within_limit(obligation.recursion_depth) =>
                 {
-                    self.selcx.infcx.err_ctxt().report_overflow_error(
-                        &obligation.predicate,
-                        obligation.cause.span,
-                        false,
-                        |_| {},
-                    );
+                    self.selcx.infcx.err_ctxt().report_overflow_obligation(&obligation, false);
                 }
 
                 ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1,6 +1,7 @@
 //! Code for projecting associated types out of trait references.
 
 use super::check_args_compatible;
+use super::error_reporting::OverflowCause;
 use super::specialization_graph;
 use super::translate_args;
 use super::util;
@@ -516,10 +517,7 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
             return ty;
         }
 
-        let (kind, data) = match *ty.kind() {
-            ty::Alias(kind, alias_ty) => (kind, alias_ty),
-            _ => return ty.super_fold_with(self),
-        };
+        let ty::Alias(kind, data) = *ty.kind() else { return ty.super_fold_with(self) };
 
         // We try to be a little clever here as a performance optimization in
         // cases where there are nested projections under binders.
@@ -554,7 +552,7 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
                         let recursion_limit = self.interner().recursion_limit();
                         if !recursion_limit.value_within_limit(self.depth) {
                             self.selcx.infcx.err_ctxt().report_overflow_error(
-                                &ty,
+                                OverflowCause::DeeplyNormalize(data),
                                 self.cause.span,
                                 true,
                                 |_| {},
@@ -664,7 +662,7 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
                 let recursion_limit = self.interner().recursion_limit();
                 if !recursion_limit.value_within_limit(self.depth) {
                     self.selcx.infcx.err_ctxt().report_overflow_error(
-                        &ty,
+                        OverflowCause::DeeplyNormalize(data),
                         self.cause.span,
                         false,
                         |diag| {

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -5,7 +5,7 @@
 use crate::infer::at::At;
 use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::{InferCtxt, InferOk};
-use crate::traits::error_reporting::TypeErrCtxtExt;
+use crate::traits::error_reporting::{OverflowCause, TypeErrCtxtExt};
 use crate::traits::project::{needs_normalization, BoundVarReplacer, PlaceholderReplacer};
 use crate::traits::{ObligationCause, PredicateObligation, Reveal};
 use rustc_data_structures::sso::SsoHashMap;
@@ -233,7 +233,11 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                             let guar = self
                                 .infcx
                                 .err_ctxt()
-                                .build_overflow_error(&ty, self.cause.span, true)
+                                .build_overflow_error(
+                                    OverflowCause::DeeplyNormalize(data),
+                                    self.cause.span,
+                                    true,
+                                )
                                 .delay_as_bug();
                             return Ok(Ty::new_error(self.interner(), guar));
                         }

compiler/rustc_type_ir/src/ty_kind.rs

@@ -105,6 +105,17 @@ pub enum AliasKind {
     Weak,
 }
 
+impl AliasKind {
+    pub fn descr(self) -> &'static str {
+        match self {
+            AliasKind::Projection => "associated type",
+            AliasKind::Inherent => "inherent associated type",
+            AliasKind::Opaque => "opaque type",
+            AliasKind::Weak => "type alias",
+        }
+    }
+}
+
 /// Defines the kinds of types used by the type system.
 ///
 /// Types written by the user start out as `hir::TyKind` and get

tests/ui/infinite/infinite-type-alias-mutual-recursion.feature.stderr

@@ -1,20 +1,20 @@
-error[E0275]: overflow evaluating the requirement `X2`
+error[E0275]: overflow normalizing the type alias `X2`
   --> $DIR/infinite-type-alias-mutual-recursion.rs:6:11
    |
 LL | type X1 = X2;
    |           ^^
    |
    = note: in case this is a recursive type alias, consider using a struct, enum, or union instead
 
-error[E0275]: overflow evaluating the requirement `X3`
+error[E0275]: overflow normalizing the type alias `X3`
   --> $DIR/infinite-type-alias-mutual-recursion.rs:9:11
    |
 LL | type X2 = X3;
    |           ^^
    |
    = note: in case this is a recursive type alias, consider using a struct, enum, or union instead
 
-error[E0275]: overflow evaluating the requirement `X1`
+error[E0275]: overflow normalizing the type alias `X1`
   --> $DIR/infinite-type-alias-mutual-recursion.rs:11:11
    |
 LL | type X3 = X1;

tests/ui/infinite/infinite-type-alias-mutual-recursion.rs

@@ -5,10 +5,10 @@
 
 type X1 = X2;
 //[gated]~^ ERROR cycle detected when expanding type alias `X1`
-//[feature]~^^ ERROR: overflow evaluating the requirement `X2`
+//[feature]~^^ ERROR: overflow normalizing the type alias `X2`
 type X2 = X3;
-//[feature]~^ ERROR: overflow evaluating the requirement `X3`
+//[feature]~^ ERROR: overflow normalizing the type alias `X3`
 type X3 = X1;
-//[feature]~^ ERROR: overflow evaluating the requirement `X1`
+//[feature]~^ ERROR: overflow normalizing the type alias `X1`
 
 fn main() {}

tests/ui/infinite/infinite-vec-type-recursion.feature.stderr

@@ -1,4 +1,4 @@
-error[E0275]: overflow evaluating the requirement `X`
+error[E0275]: overflow normalizing the type alias `X`
   --> $DIR/infinite-vec-type-recursion.rs:6:10
    |
 LL | type X = Vec<X>;

tests/ui/infinite/infinite-vec-type-recursion.rs

@@ -5,7 +5,7 @@
 
 type X = Vec<X>;
 //[gated]~^ ERROR cycle detected
-//[feature]~^^ ERROR: overflow evaluating the requirement `X`
+//[feature]~^^ ERROR: overflow normalizing the type alias `X`
 
 #[rustfmt::skip]
 fn main() { let b: X = Vec::new(); }