Semantic changes from new hir representation

Always lower to `GenericArg::Infer`
Update `PlaceholderCollector`
Update closure lifetime binder infer var visitor
Fallback visitor handle ambig infer args
Ensure type infer args have their type recorded

7 files changed, 47 insertions, 53 deletions

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index b4a9bbd09fd..933079938ae 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -1085,7 +1085,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(lt)),
             ast::GenericArg::Type(ty) => {
                 match &ty.kind {
-                    TyKind::Infer if self.tcx.features().generic_arg_infer() => {
+                    TyKind::Infer => {
                         return GenericArg::Infer(hir::InferArg {
                             hir_id: self.lower_node_id(ty.id),
                             span: self.lower_span(ty.span),
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index e0babf497e0..c44d386bc9f 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -139,29 +139,12 @@ pub(crate) struct HirPlaceholderCollector {
 }
 
 impl<'v> Visitor<'v> for HirPlaceholderCollector {
-    fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
-        if let hir::TyKind::Infer = t.kind {
-            self.spans.push(t.span);
-        }
-        intravisit::walk_ty(self, t)
-    }
-    fn visit_generic_arg(&mut self, generic_arg: &'v hir::GenericArg<'v>) {
-        match generic_arg {
-            hir::GenericArg::Infer(inf) => {
-                self.spans.push(inf.span);
-                self.may_contain_const_infer = true;
-                intravisit::walk_inf(self, inf);
-            }
-            hir::GenericArg::Type(t) => self.visit_ty(t),
-            _ => {}
-        }
-    }
-    fn visit_const_arg(&mut self, const_arg: &'v hir::ConstArg<'v>) {
-        if let hir::ConstArgKind::Infer(span) = const_arg.kind {
+    fn visit_infer(&mut self, _inf_id: HirId, inf_span: Span, kind: InferKind<'v>) -> Self::Result {
+        self.spans.push(inf_span);
+
+        if let InferKind::Const(_) | InferKind::Ambig(_) = kind {
             self.may_contain_const_infer = true;
-            self.spans.push(span);
         }
-        intravisit::walk_const_arg(self, const_arg)
     }
 }
 
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 2fae1a23f32..1c8a7d2d0be 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -489,15 +489,17 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                     struct FindInferInClosureWithBinder;
                     impl<'v> Visitor<'v> for FindInferInClosureWithBinder {
                         type Result = ControlFlow<Span>;
-                        fn visit_ty(&mut self, t: &'v hir::Ty<'v>) -> Self::Result {
-                            if matches!(t.kind, hir::TyKind::Infer) {
-                                ControlFlow::Break(t.span)
-                            } else {
-                                intravisit::walk_ty(self, t)
-                            }
+
+                        fn visit_infer(
+                            &mut self,
+                            _inf_id: HirId,
+                            inf_span: Span,
+                            _kind: InferKind<'v>,
+                        ) -> Self::Result {
+                            ControlFlow::Break(inf_span)
                         }
                     }
-                    FindInferInClosureWithBinder.visit_ty(ty).break_value()
+                    FindInferInClosureWithBinder.visit_unambig_ty(ty).break_value()
                 }
 
                 let infer_in_rt_sp = match fn_decl.output {
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
index af83d412631..fe3dcb35639 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
@@ -40,17 +40,6 @@ fn generic_arg_mismatch_err(
         param.kind.descr(),
     );
 
-    if let GenericParamDefKind::Const { .. } = param.kind {
-        if matches!(arg, GenericArg::Type(hir::Ty { kind: hir::TyKind::Infer, .. })) {
-            err.help("const arguments cannot yet be inferred with `_`");
-            tcx.disabled_nightly_features(
-                &mut err,
-                param.def_id.as_local().map(|local| tcx.local_def_id_to_hir_id(local)),
-                [(String::new(), sym::generic_arg_infer)],
-            );
-        }
-    }
-
     let add_braces_suggestion = |arg: &GenericArg<'_>, err: &mut Diag<'_>| {
         let suggestions = vec![
             (arg.span().shrink_to_lo(), String::from("{ ")),
@@ -269,6 +258,21 @@ pub fn lower_generic_args<'tcx: 'a, 'a>(
                             GenericParamDefKind::Const { .. },
                             _,
                         ) => {
+                            if let GenericParamDefKind::Const { .. } = param.kind
+                                && let GenericArg::Infer(inf) = arg
+                                && !tcx.features().generic_arg_infer()
+                            {
+                                rustc_session::parse::feature_err(
+                                    tcx.sess,
+                                    sym::generic_arg_infer,
+                                    inf.span,
+                                    "const arguments cannot yet be inferred with `_`",
+                                )
+                                .emit();
+                            }
+
+                            // We lower to an infer even when the feature gate is not enabled
+                            // as it is useful for diagnostics to be able to see a `ConstKind::Infer`
                             args.push(ctx.provided_kind(&args, param, arg));
                             args_iter.next();
                             params.next();
diff --git a/compiler/rustc_hir_typeck/src/fallback.rs b/compiler/rustc_hir_typeck/src/fallback.rs
index c128485d93e..1f3f03b9929 100644
--- a/compiler/rustc_hir_typeck/src/fallback.rs
+++ b/compiler/rustc_hir_typeck/src/fallback.rs
@@ -10,7 +10,7 @@ use rustc_hir as hir;
 use rustc_hir::HirId;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
-use rustc_hir::intravisit::Visitor;
+use rustc_hir::intravisit::{InferKind, Visitor};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable};
 use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
@@ -641,16 +641,21 @@ impl<'tcx> AnnotateUnitFallbackVisitor<'_, 'tcx> {
 impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> {
     type Result = ControlFlow<errors::SuggestAnnotation>;
 
-    fn visit_ty(&mut self, hir_ty: &'tcx hir::Ty<'tcx>) -> Self::Result {
+    fn visit_infer(
+        &mut self,
+        inf_id: HirId,
+        inf_span: Span,
+        _kind: InferKind<'tcx>,
+    ) -> Self::Result {
         // Try to replace `_` with `()`.
-        if let hir::TyKind::Infer = hir_ty.kind
-            && let Some(ty) = self.fcx.typeck_results.borrow().node_type_opt(hir_ty.hir_id)
+        if let Some(ty) = self.fcx.typeck_results.borrow().node_type_opt(inf_id)
             && let Some(vid) = self.fcx.root_vid(ty)
             && self.reachable_vids.contains(&vid)
         {
-            return ControlFlow::Break(errors::SuggestAnnotation::Unit(hir_ty.span));
+            return ControlFlow::Break(errors::SuggestAnnotation::Unit(inf_span));
         }
-        hir::intravisit::walk_ty(self, hir_ty)
+
+        ControlFlow::Continue(())
     }
 
     fn visit_qpath(
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index ca9b6e47527..d526e1ab306 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -1272,17 +1272,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         .lower_lifetime(lt, RegionInferReason::Param(param))
                         .into(),
                     (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
-                        // We handle the ambig portions of `Ty` in match arms below
+                        // We handle the ambig portions of `Ty` in match arm below
                         self.fcx.lower_ty(ty.as_unambig_ty()).raw.into()
                     }
+                    (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
+                        self.fcx.lower_ty(&inf.to_ty()).raw.into()
+                    }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
                         .fcx
                         // Ambiguous parts of `ConstArg` are handled in the match arms below
                         .lower_const_arg(ct.as_unambig_ct(), FeedConstTy::Param(param.def_id))
                         .into(),
-                    (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
-                        self.fcx.ty_infer(Some(param), inf.span).into()
-                    }
                     (&GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
                         self.fcx.ct_infer(Some(param), inf.span).into()
                     }
diff --git a/compiler/rustc_hir_typeck/src/method/confirm.rs b/compiler/rustc_hir_typeck/src/method/confirm.rs
index ced5a55712c..880ee83c80a 100644
--- a/compiler/rustc_hir_typeck/src/method/confirm.rs
+++ b/compiler/rustc_hir_typeck/src/method/confirm.rs
@@ -428,14 +428,14 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                         // We handle the ambig portions of `Ty` in the match arms below
                         self.cfcx.lower_ty(ty.as_unambig_ty()).raw.into()
                     }
+                    (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
+                        self.cfcx.lower_ty(&inf.to_ty()).raw.into()
+                    }
                     (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
                         .cfcx
                         // We handle the ambig portions of `ConstArg` in the match arms below
                         .lower_const_arg(ct.as_unambig_ct(), FeedConstTy::Param(param.def_id))
                         .into(),
-                    (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
-                        self.cfcx.ty_infer(Some(param), inf.span).into()
-                    }
                     (GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
                         self.cfcx.ct_infer(Some(param), inf.span).into()
                     }