Track WellFormed obligations with an appropriate cause, instead of MiscObligation

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -271,7 +271,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
     }
 
     fn normalize(mut self) -> Vec<traits::PredicateObligation<'tcx>> {
-        let cause = self.cause(traits::MiscObligation);
+        let cause = self.cause(traits::WellFormed(None));
         let infcx = &mut self.infcx;
         let param_env = self.param_env;
         let mut obligations = Vec::with_capacity(self.out.len());
@@ -385,7 +385,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
         self.out.extend(obligations);
 
         let tcx = self.tcx();
-        let cause = self.cause(traits::MiscObligation);
+        let cause = self.cause(traits::WellFormed(None));
         let param_env = self.param_env;
         let depth = self.recursion_depth;
 
@@ -445,7 +445,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                             let predicate =
                                 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(uv.shrink()))
                                     .to_predicate(self.tcx());
-                            let cause = self.cause(traits::MiscObligation);
+                            let cause = self.cause(traits::WellFormed(None));
                             self.out.push(traits::Obligation::with_depth(
                                 cause,
                                 self.recursion_depth,
@@ -457,7 +457,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                             let resolved = self.infcx.shallow_resolve(infer);
                             // the `InferConst` changed, meaning that we made progress.
                             if resolved != infer {
-                                let cause = self.cause(traits::MiscObligation);
+                                let cause = self.cause(traits::WellFormed(None));
 
                                 let resolved_constant = self.infcx.tcx.mk_const(ty::ConstS {
                                     kind: ty::ConstKind::Infer(resolved),
@@ -648,7 +648,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     let defer_to_coercion = self.tcx().features().object_safe_for_dispatch;
 
                     if !defer_to_coercion {
-                        let cause = self.cause(traits::MiscObligation);
+                        let cause = self.cause(traits::WellFormed(None));
                         let component_traits = data.auto_traits().chain(data.principal_def_id());
                         let tcx = self.tcx();
                         self.out.extend(component_traits.map(|did| {
@@ -679,7 +679,7 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
                     let ty = self.infcx.shallow_resolve(ty);
                     if let ty::Infer(ty::TyVar(_)) = ty.kind() {
                         // Not yet resolved, but we've made progress.
-                        let cause = self.cause(traits::MiscObligation);
+                        let cause = self.cause(traits::WellFormed(None));
                         self.out.push(traits::Obligation::with_depth(
                             cause,
                             self.recursion_depth,

compiler/rustc_typeck/src/check/callee.rs

@@ -117,7 +117,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
 
         // we must check that return type of called functions is WF:
-        self.register_wf_obligation(output.into(), call_expr.span, traits::MiscObligation);
+        self.register_wf_obligation(output.into(), call_expr.span, traits::WellFormed(None));
 
         output
     }

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -496,7 +496,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     pub fn to_ty(&self, ast_t: &hir::Ty<'_>) -> Ty<'tcx> {
         let t = <dyn AstConv<'_>>::ast_ty_to_ty(self, ast_t);
-        self.register_wf_obligation(t.into(), ast_t.span, traits::MiscObligation);
+        self.register_wf_obligation(t.into(), ast_t.span, traits::WellFormed(None));
         t
     }
 
@@ -526,7 +526,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.register_wf_obligation(
             c.into(),
             self.tcx.hir().span(ast_c.hir_id),
-            ObligationCauseCode::MiscObligation,
+            ObligationCauseCode::WellFormed(None),
         );
         c
     }
@@ -544,7 +544,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.register_wf_obligation(
             c.into(),
             self.tcx.hir().span(ast_c.hir_id),
-            ObligationCauseCode::MiscObligation,
+            ObligationCauseCode::WellFormed(None),
         );
         c
     }
@@ -607,7 +607,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         for arg in substs.iter().filter(|arg| {
             matches!(arg.unpack(), GenericArgKind::Type(..) | GenericArgKind::Const(..))
         }) {
-            self.register_wf_obligation(arg, expr.span, traits::MiscObligation);
+            self.register_wf_obligation(arg, expr.span, traits::WellFormed(None));
         }
     }
 

compiler/rustc_typeck/src/check/method/confirm.rs

@@ -501,7 +501,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         // the function type must also be well-formed (this is not
         // implied by the substs being well-formed because of inherent
         // impls and late-bound regions - see issue #28609).
-        self.register_wf_obligation(fty.into(), self.span, traits::MiscObligation);
+        self.register_wf_obligation(fty.into(), self.span, traits::WellFormed(None));
     }
 
     ///////////////////////////////////////////////////////////////////////////

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -1180,7 +1180,7 @@ fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_fo
             fcx.register_bound(
                 item_ty,
                 tcx.require_lang_item(LangItem::Sized, None),
-                traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
+                traits::ObligationCause::new(ty_span, fcx.body_id, traits::WellFormed(None)),
             );
         }
 

compiler/rustc_typeck/src/hir_wf_check.rs

@@ -72,7 +72,7 @@ fn diagnostic_hir_wf_check<'tcx>(
                 let cause = traits::ObligationCause::new(
                     ty.span,
                     self.hir_id,
-                    traits::ObligationCauseCode::MiscObligation,
+                    traits::ObligationCauseCode::WellFormed(None),
                 );
                 fulfill.register_predicate_obligation(
                     &infcx,