Auto merge of #112687 - compiler-errors:simplify-impl-source, r=lcnr

Simplify `ImplSource` candidates a bit

Reduce the number of impl source candidates, which will hopefully make our life easier when trying to adapt things like `SelectionContext::select` and `codegen_select_candidate` for the new solver.

r? `@lcnr` but feel free to reassign

2 files changed, 12 insertions, 3 deletions

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index 57d939747aa..106cf111474 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -781,8 +781,17 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                             );
                             return;
                         }
-                        Ok(Some(ImplSource::Closure(data))) => {
-                            if !tcx.is_const_fn_raw(data.closure_def_id) {
+                        // Closure: Fn{Once|Mut}
+                        Ok(Some(ImplSource::Builtin(_)))
+                            if poly_trait_pred.self_ty().skip_binder().is_closure()
+                                && tcx.fn_trait_kind_from_def_id(trait_id).is_some() =>
+                        {
+                            let ty::Closure(closure_def_id, substs) =
+                                *poly_trait_pred.self_ty().no_bound_vars().unwrap().kind()
+                            else {
+                                unreachable!()
+                            };
+                            if !tcx.is_const_fn_raw(closure_def_id) {
                                 self.check_op(ops::FnCallNonConst {
                                     caller,
                                     callee,
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
index 1da20579021..a2d23425f3b 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
@@ -172,7 +172,7 @@ impl Qualif for NeedsNonConstDrop {
 
         if !matches!(
             impl_src,
-            ImplSource::ConstDestruct(_) | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
+            ImplSource::Builtin(_) | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
         ) {
             // If our const destruct candidate is not ConstDestruct or implied by the param env,
             // then it's bad