Don't elaborate effects predicates into bounds list unless we're actually collecting implied bounds, not super bounds

compiler/rustc_hir_analysis/src/bounds.rs

@@ -9,6 +9,8 @@
 use rustc_span::def_id::DefId;
 use rustc_span::Span;
 
+use crate::hir_ty_lowering::OnlySelfBounds;
+
 /// Collects together a list of type bounds. These lists of bounds occur in many places
 /// in Rust's syntax:
 ///
@@ -50,6 +52,7 @@ pub(crate) fn push_trait_bound(
         span: Span,
         polarity: ty::PredicatePolarity,
         constness: ty::BoundConstness,
+        only_self_bounds: OnlySelfBounds,
     ) {
         let clause = (
             bound_trait_ref
@@ -66,7 +69,10 @@ pub(crate) fn push_trait_bound(
             self.clauses.push(clause);
         }
 
-        if !tcx.features().effects {
+        // FIXME(effects): Lift this out of `push_trait_bound`, and move it somewhere else.
+        // Perhaps moving this into `lower_poly_trait_ref`, just like we lower associated
+        // type bounds.
+        if !tcx.features().effects || only_self_bounds.0 {
             return;
         }
         // For `T: ~const Tr` or `T: const Tr`, we need to add an additional bound on the

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -719,6 +719,7 @@ pub(crate) fn lower_poly_trait_ref(
             span,
             polarity,
             constness,
+            only_self_bounds,
         );
 
         let mut dup_constraints = FxIndexMap::default();

tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.rs

@@ -39,7 +39,6 @@ impl const Foo for NonConstAdd {
 #[const_trait]
 trait Baz {
     type Qux: Add;
-    //~^ ERROR the trait bound
 }
 
 impl const Baz for NonConstAdd {

tests/ui/rfcs/rfc-2632-const-trait-impl/assoc-type.stderr

@@ -12,17 +12,5 @@ error: using `#![feature(effects)]` without enabling next trait solver globally
    = note: the next trait solver must be enabled globally for the effects feature to work correctly
    = help: use `-Znext-solver` to enable
 
-error[E0277]: the trait bound `Add::{synthetic#0}: Compat` is not satisfied
+error: aborting due to 1 previous error; 1 warning emitted
-  --> $DIR/assoc-type.rs:41:15
-   |
-LL |     type Qux: Add;
-   |               ^^^ the trait `Compat` is not implemented for `Add::{synthetic#0}`
-   |
-help: consider further restricting the associated type
-   |
-LL | trait Baz where Add::{synthetic#0}: Compat {
-   |           ++++++++++++++++++++++++++++++++
 
-error: aborting due to 2 previous errors; 1 warning emitted
-
-For more information about this error, try `rustc --explain E0277`.