Rollup merge of #129523 - lqd:stable-type-ir, r=compiler-errors

Make `rustc_type_ir` build on stable

This PR fixes a handful of issues that appear in `rustc_type_ir` when trying to build the new solver on stable.

r? ```@compiler-errors```
```@bors``` rollup

4 files changed, 8 insertions, 2 deletions

diff --git a/compiler/rustc_type_ir/Cargo.toml b/compiler/rustc_type_ir/Cargo.toml
index 2750838bbe9..785fa5e386a 100644
--- a/compiler/rustc_type_ir/Cargo.toml
+++ b/compiler/rustc_type_ir/Cargo.toml
@@ -31,3 +31,6 @@ nightly = [
     "rustc_index/nightly",
     "rustc_ast_ir/nightly"
 ]
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bootstrap)'] }
diff --git a/compiler/rustc_type_ir/src/elaborate.rs b/compiler/rustc_type_ir/src/elaborate.rs
index f30419c801f..433c444e701 100644
--- a/compiler/rustc_type_ir/src/elaborate.rs
+++ b/compiler/rustc_type_ir/src/elaborate.rs
@@ -237,7 +237,7 @@ pub fn supertrait_def_ids<I: Interner>(
     cx: I,
     trait_def_id: I::DefId,
 ) -> impl Iterator<Item = I::DefId> {
-    let mut set = HashSet::default();
+    let mut set: HashSet<I::DefId> = HashSet::default();
     let mut stack = vec![trait_def_id];
 
     set.insert(trait_def_id);
diff --git a/compiler/rustc_type_ir/src/outlives.rs b/compiler/rustc_type_ir/src/outlives.rs
index bfcea6a81d3..e8afaf1a480 100644
--- a/compiler/rustc_type_ir/src/outlives.rs
+++ b/compiler/rustc_type_ir/src/outlives.rs
@@ -68,6 +68,9 @@ struct OutlivesCollector<'a, I: Interner> {
 }
 
 impl<I: Interner> TypeVisitor<I> for OutlivesCollector<'_, I> {
+    #[cfg(not(feature = "nightly"))]
+    type Result = ();
+
     fn visit_ty(&mut self, ty: I::Ty) -> Self::Result {
         if !self.visited.insert(ty) {
             return;
diff --git a/compiler/rustc_type_ir/src/search_graph/mod.rs b/compiler/rustc_type_ir/src/search_graph/mod.rs
index d47c9e725f3..418139c3aad 100644
--- a/compiler/rustc_type_ir/src/search_graph/mod.rs
+++ b/compiler/rustc_type_ir/src/search_graph/mod.rs
@@ -287,7 +287,7 @@ impl<X: Cx> NestedGoals<X> {
         }
     }
 
-    #[rustc_lint_query_instability]
+    #[cfg_attr(feature = "nightly", rustc_lint_query_instability)]
     #[allow(rustc::potential_query_instability)]
     fn iter(&self) -> impl Iterator<Item = (X::Input, UsageKind)> + '_ {
         self.nested_goals.iter().map(|(i, p)| (*i, *p))