Rollup merge of rust-lang#90375 - yanok:master, r=lcnr

Use `is_global` in `candidate_should_be_dropped_in_favor_of`

This manifistated in rust-lang#90195 with compiler being unable to keep
one candidate for a trait impl, if where is a global impl and more
than one trait bound in the where clause.

Before rust-lang#87280 `candidate_should_be_dropped_in_favor_of` was using
`TypeFoldable::is_global()` that was enough to discard the two
`ParamCandidate`s. But rust-lang#87280 changed it to use
`TypeFoldable::is_known_global()` instead, which is pessimistic, so
now the compiler drops the global impl instead (because
`is_known_global` is not sure) and then can't decide between the
two `ParamCandidate`s.

Switching it to use `is_global` again solves the issue.

Fixes rust-lang#90195.

Author: GuillaumeGomez

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

@@ -1547,8 +1547,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Check if a bound would previously have been removed when normalizing
         // the param_env so that it can be given the lowest priority. See
         // #50825 for the motivation for this.
-        let is_global =
-            |cand: &ty::PolyTraitRef<'_>| cand.is_known_global() && !cand.has_late_bound_regions();
+        let is_global = |cand: &ty::PolyTraitRef<'tcx>| {
+            cand.is_global(self.infcx.tcx) && !cand.has_late_bound_regions()
+        };
 
         // (*) Prefer `BuiltinCandidate { has_nested: false }`, `PointeeCandidate`,
         // and `DiscriminantKindCandidate` to anything else.

src/test/ui/traits/issue-90195-2.rs

@@ -0,0 +1,20 @@
+// check-pass
+pub trait Archive {
+    type Archived;
+}
+
+impl<T> Archive for Option<T> {
+    type Archived = ();
+}
+pub type Archived<T> = <T as Archive>::Archived;
+
+pub trait Deserialize<D> {}
+
+const ARRAY_SIZE: usize = 32;
+impl<__D> Deserialize<__D> for ()
+where
+    Option<[u8; ARRAY_SIZE]>: Archive,
+    Archived<Option<[u8; ARRAY_SIZE]>>: Deserialize<__D>,
+{
+}
+fn main() {}

src/test/ui/traits/issue-90195.rs

@@ -0,0 +1,21 @@
+// check-pass
+pub trait Archive {
+    type Archived;
+}
+
+impl<T> Archive for Option<T> {
+    type Archived = ();
+}
+pub type Archived<T> = <T as Archive>::Archived;
+
+pub trait Deserialize<D> {}
+
+const ARRAY_SIZE: usize = 32;
+impl<__D> Deserialize<__D> for ()
+where
+    Option<[u8; ARRAY_SIZE]>: Archive,
+    Option<[u8; ARRAY_SIZE]>: Archive,
+    Archived<Option<[u8; ARRAY_SIZE]>>: Deserialize<__D>,
+{
+}
+fn main() {}