[experiment] Test perf when unconditionally EvaluatedToUnknown on inductive cycles

compiler/rustc_middle/src/ty/mod.rs

@@ -238,7 +238,7 @@ pub struct ImplHeader<'tcx> {
     pub impl_def_id: DefId,
     pub self_ty: Ty<'tcx>,
     pub trait_ref: Option<TraitRef<'tcx>>,
-    pub predicates: Vec<(Predicate<'tcx>, Span)>,
+    pub predicates: Vec<Predicate<'tcx>>,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TypeFoldable, TypeVisitable)]

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -24,7 +24,6 @@ use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitor};
-use rustc_session::lint::builtin::COINDUCTIVE_OVERLAP_IN_COHERENCE;
 use rustc_span::symbol::sym;
 use rustc_span::DUMMY_SP;
 use std::fmt::Debug;
@@ -152,16 +151,14 @@ fn with_fresh_ty_vars<'cx, 'tcx>(
             .predicates_of(impl_def_id)
             .instantiate(tcx, impl_args)
             .iter()
-            .map(|(c, s)| (c.as_predicate(), s))
+            .map(|(c, _)| c.as_predicate())
             .collect(),
     };
 
-    let InferOk { value: mut header, obligations } = selcx
-        .infcx
-        .at(&ObligationCause::dummy_with_span(tcx.def_span(impl_def_id)), param_env)
-        .normalize(header);
+    let InferOk { value: mut header, obligations } =
+        selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(header);
 
-    header.predicates.extend(obligations.into_iter().map(|o| (o.predicate, o.cause.span)));
+    header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
     header
 }
 
@@ -191,7 +188,8 @@ fn overlap<'tcx>(
         .intercrate(true)
         .with_next_trait_solver(tcx.next_trait_solver_in_coherence())
         .build();
-    let selcx = &mut SelectionContext::new(&infcx);
+    let selcx =
+        &mut SelectionContext::with_treat_inductive_cycle_as(&infcx, TreatInductiveCycleAs::Recur);
     if track_ambiguity_causes.is_yes() {
         selcx.enable_tracking_intercrate_ambiguity_causes();
     }
@@ -211,74 +209,14 @@ fn overlap<'tcx>(
     debug!("overlap: unification check succeeded");
 
     if overlap_mode.use_implicit_negative() {
-        for mode in [TreatInductiveCycleAs::Ambig, TreatInductiveCycleAs::Recur] {
-            if let Some(failing_obligation) = selcx.with_treat_inductive_cycle_as(mode, |selcx| {
-                impl_intersection_has_impossible_obligation(
-                    selcx,
-                    param_env,
-                    &impl1_header,
-                    &impl2_header,
-                    &equate_obligations,
-                )
-            }) {
-                if matches!(mode, TreatInductiveCycleAs::Recur) {
-                    let first_local_impl = impl1_header
-                        .impl_def_id
-                        .as_local()
-                        .or(impl2_header.impl_def_id.as_local())
-                        .expect("expected one of the impls to be local");
-                    infcx.tcx.struct_span_lint_hir(
-                        COINDUCTIVE_OVERLAP_IN_COHERENCE,
-                        infcx.tcx.local_def_id_to_hir_id(first_local_impl),
-                        infcx.tcx.def_span(first_local_impl),
-                        format!(
-                            "implementations {} will conflict in the future",
-                            match impl1_header.trait_ref {
-                                Some(trait_ref) => {
-                                    let trait_ref = infcx.resolve_vars_if_possible(trait_ref);
-                                    format!(
-                                        "of `{}` for `{}`",
-                                        trait_ref.print_only_trait_path(),
-                                        trait_ref.self_ty()
-                                    )
-                                }
-                                None => format!(
-                                    "for `{}`",
-                                    infcx.resolve_vars_if_possible(impl1_header.self_ty)
-                                ),
-                            },
-                        ),
-                        |lint| {
-                            lint.note(
-                                "impls that are not considered to overlap may be considered to \
-                                overlap in the future",
-                            )
-                            .span_label(
-                                infcx.tcx.def_span(impl1_header.impl_def_id),
-                                "the first impl is here",
-                            )
-                            .span_label(
-                                infcx.tcx.def_span(impl2_header.impl_def_id),
-                                "the second impl is here",
-                            );
-                            if !failing_obligation.cause.span.is_dummy() {
-                                lint.span_label(
-                                    failing_obligation.cause.span,
-                                    format!(
-                                        "`{}` may be considered to hold in future releases, \
-                                        causing the impls to overlap",
-                                        infcx
-                                            .resolve_vars_if_possible(failing_obligation.predicate)
-                                    ),
-                                );
-                            }
-                            lint
-                        },
-                    );
-                }
-
-                return None;
-            }
+        if let Some(_failing_obligation) = impl_intersection_has_impossible_obligation(
+            selcx,
+            param_env,
+            &impl1_header,
+            &impl2_header,
+            &equate_obligations,
+        ) {
+            return None;
         }
     }
 
@@ -355,8 +293,8 @@ fn impl_intersection_has_impossible_obligation<'cx, 'tcx>(
     [&impl1_header.predicates, &impl2_header.predicates]
         .into_iter()
         .flatten()
-        .map(|&(predicate, span)| {
-            Obligation::new(infcx.tcx, ObligationCause::dummy_with_span(span), param_env, predicate)
+        .map(|&predicate| {
+            Obligation::new(infcx.tcx, ObligationCause::dummy(), param_env, predicate)
         })
         .chain(obligations.into_iter().cloned())
         .find(|obligation: &PredicateObligation<'tcx>| {

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -233,19 +233,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     }
 
     // Sets the `TreatInductiveCycleAs` mode temporarily in the selection context
-    pub fn with_treat_inductive_cycle_as<T>(
-        &mut self,
+    pub fn with_treat_inductive_cycle_as(
+        infcx: &'cx InferCtxt<'tcx>,
         treat_inductive_cycle: TreatInductiveCycleAs,
-        f: impl FnOnce(&mut Self) -> T,
-    ) -> T {
-        // Should be executed in a context where caching is disabled,
-        // otherwise the cache is poisoned with the temporary result.
-        assert!(self.is_intercrate());
-        let treat_inductive_cycle =
-            std::mem::replace(&mut self.treat_inductive_cycle, treat_inductive_cycle);
-        let value = f(self);
-        self.treat_inductive_cycle = treat_inductive_cycle;
-        value
+    ) -> SelectionContext<'cx, 'tcx> {
+        SelectionContext { treat_inductive_cycle, ..SelectionContext::new(infcx) }
     }
 
     pub fn with_query_mode(

tests/ui/traits/issue-105231.rs

@@ -1,9 +1,9 @@
+//~ ERROR overflow evaluating the requirement `A<A<A<A<A<A<A<...>>>>>>>: Send`
 struct A<T>(B<T>);
 //~^ ERROR recursive types `A` and `B` have infinite size
 struct B<T>(A<A<T>>);
 trait Foo {}
 impl<T> Foo for T where T: Send {}
-//~^ ERROR overflow evaluating the requirement `A<A<A<A<A<A<A<...>>>>>>>: Send`
 impl Foo for B<u8> {}
 
 fn main() {}

tests/ui/traits/issue-105231.stderr

@@ -1,5 +1,5 @@
 error[E0072]: recursive types `A` and `B` have infinite size
-  --> $DIR/issue-105231.rs:1:1
+  --> $DIR/issue-105231.rs:2:1
    |
 LL | struct A<T>(B<T>);
    | ^^^^^^^^^^^ ---- recursive without indirection
@@ -15,14 +15,10 @@ LL ~ struct B<T>(Box<A<A<T>>>);
    |
 
 error[E0275]: overflow evaluating the requirement `A<A<A<A<A<A<A<...>>>>>>>: Send`
-  --> $DIR/issue-105231.rs:5:28
-   |
-LL | impl<T> Foo for T where T: Send {}
-   |                            ^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_105231`)
 note: required because it appears within the type `B<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<A<u8>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
-  --> $DIR/issue-105231.rs:3:8
+  --> $DIR/issue-105231.rs:4:8
    |
 LL | struct B<T>(A<A<T>>);
    |        ^

tests/ui/traits/solver-cycles/cycle-via-builtin-auto-trait-impl.rs

@@ -1,3 +1,4 @@
+//~ ERROR overflow
 // A regression test for #111729 checking that we correctly
 // track recursion depth for obligations returned by confirmation.
 use std::panic::RefUnwindSafe;
@@ -14,7 +15,6 @@ struct RootDatabase {
 }
 
 impl<T: RefUnwindSafe> Database for T {
-    //~^ ERROR overflow
     type Storage = SalsaStorage;
 }
 impl Database for RootDatabase {

tests/ui/traits/solver-cycles/cycle-via-builtin-auto-trait-impl.stderr

@@ -1,17 +1,13 @@
 error[E0275]: overflow evaluating the requirement `Runtime<RootDatabase>: RefUnwindSafe`
-  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:16:9
-   |
-LL | impl<T: RefUnwindSafe> Database for T {
-   |         ^^^^^^^^^^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`cycle_via_builtin_auto_trait_impl`)
 note: required because it appears within the type `RootDatabase`
-  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:12:8
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:13:8
    |
 LL | struct RootDatabase {
    |        ^^^^^^^^^^^^
 note: required for `RootDatabase` to implement `Database`
-  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:16:24
+  --> $DIR/cycle-via-builtin-auto-trait-impl.rs:17:24
    |
 LL | impl<T: RefUnwindSafe> Database for T {
    |         -------------  ^^^^^^^^     ^