Split hir TyKind and ConstArgKind in two and update hir::Visitor

Author: BoxyUwU

compiler/rustc_ast_lowering/src/index.rs

@@ -1,3 +1,4 @@
+use intravisit::InferKind;
 use rustc_data_structures::sorted_map::SortedMap;
 use rustc_hir as hir;
 use rustc_hir::def_id::{LocalDefId, LocalDefIdMap};
@@ -258,14 +259,6 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         });
     }
 
-    fn visit_const_arg(&mut self, const_arg: &'hir ConstArg<'hir>) {
-        self.insert(const_arg.span(), const_arg.hir_id, Node::ConstArg(const_arg));
-
-        self.with_parent(const_arg.hir_id, |this| {
-            intravisit::walk_const_arg(this, const_arg);
-        });
-    }
-
     fn visit_expr(&mut self, expr: &'hir Expr<'hir>) {
         self.insert(expr.span, expr.hir_id, Node::Expr(expr));
 
@@ -295,22 +288,41 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         intravisit::walk_path_segment(self, path_segment);
     }
 
-    fn visit_ty(&mut self, ty: &'hir Ty<'hir>) {
-        self.insert(ty.span, ty.hir_id, Node::Ty(ty));
+    fn visit_ty(&mut self, ty: &'hir Ty<'hir, AmbigArg>) {
+        self.insert(ty.span, ty.hir_id, Node::Ty(ty.as_unambig_ty()));
 
         self.with_parent(ty.hir_id, |this| {
             intravisit::walk_ty(this, ty);
         });
     }
 
-    fn visit_infer(&mut self, inf: &'hir InferArg) {
-        self.insert(inf.span, inf.hir_id, Node::Infer(inf));
+    fn visit_const_arg(&mut self, const_arg: &'hir ConstArg<'hir, AmbigArg>) {
+        self.insert(
+            const_arg.as_unambig_ct().span(),
+            const_arg.hir_id,
+            Node::ConstArg(const_arg.as_unambig_ct()),
+        );
 
-        self.with_parent(inf.hir_id, |this| {
-            intravisit::walk_inf(this, inf);
+        self.with_parent(const_arg.hir_id, |this| {
+            intravisit::walk_ambig_const_arg(this, const_arg);
         });
     }
 
+    fn visit_infer(
+        &mut self,
+        inf_id: HirId,
+        inf_span: Span,
+        kind: InferKind<'hir>,
+    ) -> Self::Result {
+        match kind {
+            InferKind::Ty(ty) => self.insert(inf_span, inf_id, Node::Ty(ty)),
+            InferKind::Const(ct) => self.insert(inf_span, inf_id, Node::ConstArg(ct)),
+            InferKind::Ambig(inf) => self.insert(inf_span, inf_id, Node::Infer(inf)),
+        }
+
+        self.visit_id(inf_id);
+    }
+
     fn visit_trait_ref(&mut self, tr: &'hir TraitRef<'hir>) {
         self.insert(tr.path.span, tr.hir_ref_id, Node::TraitRef(tr));
 

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),
@@ -1111,15 +1111,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
                                 let ct =
                                     self.lower_const_path_to_const_arg(path, res, ty.id, ty.span);
-                                return GenericArg::Const(ct);
+                                return GenericArg::Const(ct.try_as_ambig_ct().unwrap());
                             }
                         }
                     }
                     _ => {}
                 }
-                GenericArg::Type(self.lower_ty(ty, itctx))
+                GenericArg::Type(self.lower_ty(ty, itctx).try_as_ambig_ty().unwrap())
+            }
+            ast::GenericArg::Const(ct) => {
+                GenericArg::Const(self.lower_anon_const_to_const_arg(ct).try_as_ambig_ct().unwrap())
             }
-            ast::GenericArg::Const(ct) => GenericArg::Const(self.lower_anon_const_to_const_arg(ct)),
         }
     }
 
@@ -1189,7 +1191,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
     fn lower_ty_direct(&mut self, t: &Ty, itctx: ImplTraitContext) -> hir::Ty<'hir> {
         let kind = match &t.kind {
-            TyKind::Infer => hir::TyKind::Infer,
+            TyKind::Infer => hir::TyKind::Infer(()),
             TyKind::Err(guar) => hir::TyKind::Err(*guar),
             TyKind::Slice(ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
             TyKind::Ptr(mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
@@ -2045,7 +2047,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     )
                     .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
                 }
-                let ct_kind = hir::ConstArgKind::Infer(self.lower_span(c.value.span));
+                let ct_kind = hir::ConstArgKind::Infer(self.lower_span(c.value.span), ());
                 self.arena.alloc(hir::ConstArg { hir_id: self.lower_node_id(c.id), kind: ct_kind })
             }
             _ => self.lower_anon_const_to_const_arg(c),

compiler/rustc_ast_lowering/src/path.rs

@@ -525,7 +525,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
             FnRetTy::Default(_) => self.arena.alloc(self.ty_tup(*span, &[])),
         };
-        let args = smallvec![GenericArg::Type(self.arena.alloc(self.ty_tup(*inputs_span, inputs)))];
+        let args = smallvec![GenericArg::Type(
+            self.arena.alloc(self.ty_tup(*inputs_span, inputs)).try_as_ambig_ty().unwrap()
+        )];
 
         // If we have a bound like `async Fn() -> T`, make sure that we mark the
         // `Output = T` associated type bound with the right feature gates.

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -8,7 +8,7 @@ use rustc_hir::QPath::Resolved;
 use rustc_hir::WherePredicateKind::BoundPredicate;
 use rustc_hir::def::Res::Def;
 use rustc_hir::def_id::DefId;
-use rustc_hir::intravisit::Visitor;
+use rustc_hir::intravisit::VisitorExt;
 use rustc_hir::{PolyTraitRef, TyKind, WhereBoundPredicate};
 use rustc_infer::infer::{NllRegionVariableOrigin, RelateParamBound};
 use rustc_middle::bug;
@@ -987,7 +987,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         for found_did in found_dids {
             let mut traits = vec![];
             let mut hir_v = HirTraitObjectVisitor(&mut traits, *found_did);
-            hir_v.visit_ty(self_ty);
+            hir_v.visit_unambig_ty(self_ty);
             debug!("trait spans found: {:?}", traits);
             for span in &traits {
                 let mut multi_span: MultiSpan = vec![*span].into();

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -432,7 +432,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
             // must highlight the variable.
             // NOTE(eddyb) this is handled in/by the sole caller
             // (`give_name_if_anonymous_region_appears_in_arguments`).
-            hir::TyKind::Infer => None,
+            hir::TyKind::Infer(()) => None,
 
             _ => Some(argument_hir_ty),
         }
@@ -615,7 +615,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
                 }
 
                 (GenericArgKind::Type(ty), hir::GenericArg::Type(hir_ty)) => {
-                    search_stack.push((ty, hir_ty));
+                    search_stack.push((ty, hir_ty.as_unambig_ty()));
                 }
 
                 (GenericArgKind::Const(_ct), hir::GenericArg::Const(_hir_ct)) => {

compiler/rustc_hir/src/hir.rs

@@ -31,7 +31,7 @@ use crate::LangItem;
 use crate::def::{CtorKind, DefKind, Res};
 use crate::def_id::{DefId, LocalDefIdMap};
 pub(crate) use crate::hir_id::{HirId, ItemLocalId, ItemLocalMap, OwnerId};
-use crate::intravisit::FnKind;
+use crate::intravisit::{FnKind, VisitorExt};
 
 #[derive(Debug, Copy, Clone, HashStable_Generic)]
 pub struct Lifetime {
@@ -263,10 +263,34 @@ impl<'hir> PathSegment<'hir> {
 /// that are [just paths](ConstArgKind::Path) (currently just bare const params)
 /// versus const args that are literals or have arbitrary computations (e.g., `{ 1 + 3 }`).
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
-pub struct ConstArg<'hir> {
+#[repr(C)]
+pub struct ConstArg<'hir, Unambig = ()> {
     #[stable_hasher(ignore)]
     pub hir_id: HirId,
-    pub kind: ConstArgKind<'hir>,
+    pub kind: ConstArgKind<'hir, Unambig>,
+}
+
+impl<'hir> ConstArg<'hir, AmbigArg> {
+    pub fn as_unambig_ct(&self) -> &ConstArg<'hir> {
+        // SAFETY: `ConstArg` is `repr(C)` and `ConstArgKind` is marked `repr(u8)` so that the
+        // layout is the same across different ZST type arguments.
+        let ptr = self as *const ConstArg<'hir, AmbigArg> as *const ConstArg<'hir, ()>;
+        unsafe { &*ptr }
+    }
+}
+
+impl<'hir> ConstArg<'hir> {
+    pub fn try_as_ambig_ct(&self) -> Option<&ConstArg<'hir, AmbigArg>> {
+        if let ConstArgKind::Infer(_, ()) = self.kind {
+            return None;
+        }
+
+        // SAFETY: `ConstArg` is `repr(C)` and `ConstArgKind` is marked `repr(u8)` so that the layout is
+        // the same across different ZST type arguments. We also asserted that the `self` is
+        // not a `ConstArgKind::Infer` so there is no risk of transmuting a `()` to `AmbigArg`.
+        let ptr = self as *const ConstArg<'hir> as *const ConstArg<'hir, AmbigArg>;
+        Some(unsafe { &*ptr })
+    }
 }
 
 impl<'hir> ConstArg<'hir> {
@@ -281,14 +305,15 @@ impl<'hir> ConstArg<'hir> {
         match self.kind {
             ConstArgKind::Path(path) => path.span(),
             ConstArgKind::Anon(anon) => anon.span,
-            ConstArgKind::Infer(span) => span,
+            ConstArgKind::Infer(span, _) => span,
         }
     }
 }
 
 /// See [`ConstArg`].
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
-pub enum ConstArgKind<'hir> {
+#[repr(u8, C)]
+pub enum ConstArgKind<'hir, Unambig = ()> {
     /// **Note:** Currently this is only used for bare const params
     /// (`N` where `fn foo<const N: usize>(...)`),
     /// not paths to any const (`N` where `const N: usize = ...`).
@@ -300,7 +325,7 @@ pub enum ConstArgKind<'hir> {
     /// `ConstArgKind::Infer`. In cases where it is ambiguous whether
     /// a generic arg is a type or a const, inference variables are
     /// represented as `GenericArg::Infer` instead.
-    Infer(Span),
+    Infer(Span, Unambig),
 }
 
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
@@ -311,15 +336,15 @@ pub struct InferArg {
 
 impl InferArg {
     pub fn to_ty(&self) -> Ty<'static> {
-        Ty { kind: TyKind::Infer, span: self.span, hir_id: self.hir_id }
+        Ty { kind: TyKind::Infer(()), span: self.span, hir_id: self.hir_id }
     }
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum GenericArg<'hir> {
     Lifetime(&'hir Lifetime),
-    Type(&'hir Ty<'hir>),
-    Const(&'hir ConstArg<'hir>),
+    Type(&'hir Ty<'hir, AmbigArg>),
+    Const(&'hir ConstArg<'hir, AmbigArg>),
     /// **Note:** Inference variables are only represented as
     /// `GenericArg::Infer` in cases where it is ambiguous whether
     /// a generic arg is a type or a const. Otherwise, inference variables
@@ -332,7 +357,7 @@ impl GenericArg<'_> {
         match self {
             GenericArg::Lifetime(l) => l.ident.span,
             GenericArg::Type(t) => t.span,
-            GenericArg::Const(c) => c.span(),
+            GenericArg::Const(c) => c.as_unambig_ct().span(),
             GenericArg::Infer(i) => i.span,
         }
     }
@@ -351,7 +376,7 @@ impl GenericArg<'_> {
             GenericArg::Lifetime(_) => "lifetime",
             GenericArg::Type(_) => "type",
             GenericArg::Const(_) => "constant",
-            GenericArg::Infer(_) => "inferred",
+            GenericArg::Infer(_) => "placeholder",
         }
     }
 
@@ -2904,10 +2929,37 @@ impl<'hir> AssocItemConstraintKind<'hir> {
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
-pub struct Ty<'hir> {
+pub enum AmbigArg {}
+
+#[derive(Debug, Clone, Copy, HashStable_Generic)]
+#[repr(C)]
+pub struct Ty<'hir, Unambig = ()> {
     pub hir_id: HirId,
-    pub kind: TyKind<'hir>,
     pub span: Span,
+    pub kind: TyKind<'hir, Unambig>,
+}
+
+impl<'hir> Ty<'hir, AmbigArg> {
+    pub fn as_unambig_ty(&self) -> &Ty<'hir> {
+        // SAFETY: `Ty` is `repr(C)` and `TyKind` is marked `repr(u8)` so that the layout is
+        // the same across different ZST type arguments.
+        let ptr = self as *const Ty<'hir, AmbigArg> as *const Ty<'hir, ()>;
+        unsafe { &*ptr }
+    }
+}
+
+impl<'hir> Ty<'hir> {
+    pub fn try_as_ambig_ty(&self) -> Option<&Ty<'hir, AmbigArg>> {
+        if let TyKind::Infer(()) = self.kind {
+            return None;
+        }
+
+        // SAFETY: `Ty` is `repr(C)` and `TyKind` is marked `repr(u8)` so that the layout is
+        // the same across different ZST type arguments. We also asserted that the `self` is
+        // not a `TyKind::Infer` so there is no risk of transmuting a `()` to `AmbigArg`.
+        let ptr = self as *const Ty<'hir> as *const Ty<'hir, AmbigArg>;
+        Some(unsafe { &*ptr })
+    }
 }
 
 impl<'hir> Ty<'hir> {
@@ -2939,7 +2991,7 @@ impl<'hir> Ty<'hir> {
         use crate::intravisit::Visitor;
         struct MyVisitor(Vec<Span>);
         impl<'v> Visitor<'v> for MyVisitor {
-            fn visit_ty(&mut self, t: &'v Ty<'v>) {
+            fn visit_ty(&mut self, t: &'v Ty<'v, AmbigArg>) {
                 if matches!(
                     &t.kind,
                     TyKind::Path(QPath::Resolved(_, Path {
@@ -2955,7 +3007,7 @@ impl<'hir> Ty<'hir> {
         }
 
         let mut my_visitor = MyVisitor(vec![]);
-        my_visitor.visit_ty(self);
+        my_visitor.visit_unambig_ty(self);
         my_visitor.0
     }
 
@@ -2964,14 +3016,14 @@ impl<'hir> Ty<'hir> {
     pub fn is_suggestable_infer_ty(&self) -> bool {
         fn are_suggestable_generic_args(generic_args: &[GenericArg<'_>]) -> bool {
             generic_args.iter().any(|arg| match arg {
-                GenericArg::Type(ty) => ty.is_suggestable_infer_ty(),
+                GenericArg::Type(ty) => ty.as_unambig_ty().is_suggestable_infer_ty(),
                 GenericArg::Infer(_) => true,
                 _ => false,
             })
         }
         debug!(?self);
         match &self.kind {
-            TyKind::Infer => true,
+            TyKind::Infer(()) => true,
             TyKind::Slice(ty) => ty.is_suggestable_infer_ty(),
             TyKind::Array(ty, length) => {
                 ty.is_suggestable_infer_ty() || matches!(length.kind, ConstArgKind::Infer(..))
@@ -3183,7 +3235,9 @@ pub enum InferDelegationKind {
 
 /// The various kinds of types recognized by the compiler.
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
-pub enum TyKind<'hir> {
+// SAFETY: `repr(u8)` is required so that `TyKind<()>` and `TyKind<!>` are layout compatible
+#[repr(u8, C)]
+pub enum TyKind<'hir, Unambig = ()> {
     /// Actual type should be inherited from `DefId` signature
     InferDelegation(DefId, InferDelegationKind),
     /// A variable length slice (i.e., `[T]`).
@@ -3216,18 +3270,18 @@ pub enum TyKind<'hir> {
     TraitObject(&'hir [PolyTraitRef<'hir>], TaggedRef<'hir, Lifetime, TraitObjectSyntax>),
     /// Unused for now.
     Typeof(&'hir AnonConst),
+    /// Placeholder for a type that has failed to be defined.
+    Err(rustc_span::ErrorGuaranteed),
+    /// Pattern types (`pattern_type!(u32 is 1..)`)
+    Pat(&'hir Ty<'hir>, &'hir Pat<'hir>),
     /// `TyKind::Infer` means the type should be inferred instead of it having been
     /// specified. This can appear anywhere in a type.
     ///
     /// **Note:** Not all inferred types are represented as
     /// `TyKind::Infer`. In cases where it is ambiguous whether
     /// a generic arg is a type or a const, inference variables are
     /// represented as `GenericArg::Infer` instead.
-    Infer,
-    /// Placeholder for a type that has failed to be defined.
-    Err(rustc_span::ErrorGuaranteed),
-    /// Pattern types (`pattern_type!(u32 is 1..)`)
-    Pat(&'hir Ty<'hir>, &'hir Pat<'hir>),
+    Infer(Unambig),
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]