Misc cleanups of generic_arg_infer related HIR logic

compiler/rustc_ast_lowering/src/index.rs

@@ -311,7 +311,7 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         );
 
         self.with_parent(const_arg.hir_id, |this| {
-            intravisit::walk_ambig_const_arg(this, const_arg);
+            intravisit::walk_const_arg(this, const_arg);
         });
     }
 

compiler/rustc_hir/src/hir.rs

@@ -407,10 +407,8 @@ 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 }`).
 ///
-/// The `Unambig` generic parameter represents whether the position this const is from is
-/// unambiguously a const or ambiguous as to whether it is a type or a const. When in an
-/// ambiguous context the parameter is instantiated with an uninhabited type making the
-/// [`ConstArgKind::Infer`] variant unusable and [`GenericArg::Infer`] is used instead.
+/// For an explanation of the `Unambig` generic parameter see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
 #[repr(C)]
 pub struct ConstArg<'hir, Unambig = ()> {
@@ -429,6 +427,9 @@ impl<'hir> ConstArg<'hir, AmbigArg> {
     /// In practice this may mean overriding the [`Visitor::visit_infer`][visit_infer] method on hir visitors, or
     /// specifically matching on [`GenericArg::Infer`] when handling generic arguments.
     ///
+    /// For an explanation of what it means for a const arg to be ambig or unambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
+    ///
     /// [visit_infer]: [rustc_hir::intravisit::Visitor::visit_infer]
     pub fn as_unambig_ct(&self) -> &ConstArg<'hir> {
         // SAFETY: `ConstArg` is `repr(C)` and `ConstArgKind` is marked `repr(u8)` so that the
@@ -444,6 +445,9 @@ impl<'hir> ConstArg<'hir> {
     ///
     /// Functions accepting ambiguous consts will not handle the [`ConstArgKind::Infer`] variant, if
     /// infer consts are relevant to you then care should be taken to handle them separately.
+    ///
+    /// For an explanation of what it means for a const arg to be ambig or unambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
     pub fn try_as_ambig_ct(&self) -> Option<&ConstArg<'hir, AmbigArg>> {
         if let ConstArgKind::Infer(_, ()) = self.kind {
             return None;
@@ -475,6 +479,9 @@ impl<'hir, Unambig> ConstArg<'hir, Unambig> {
 }
 
 /// See [`ConstArg`].
+///
+/// For an explanation of the `Unambig` generic parameter see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
 #[derive(Clone, Copy, Debug, HashStable_Generic)]
 #[repr(u8, C)]
 pub enum ConstArgKind<'hir, Unambig = ()> {
@@ -3302,10 +3309,8 @@ pub enum AmbigArg {}
 #[repr(C)]
 /// Represents a type in the `HIR`.
 ///
-/// The `Unambig` generic parameter represents whether the position this type is from is
-/// unambiguously a type or ambiguous as to whether it is a type or a const. When in an
-/// ambiguous context the parameter is instantiated with an uninhabited type making the
-/// [`TyKind::Infer`] variant unusable and [`GenericArg::Infer`] is used instead.
+/// For an explanation of the `Unambig` generic parameter see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
 pub struct Ty<'hir, Unambig = ()> {
     #[stable_hasher(ignore)]
     pub hir_id: HirId,
@@ -3323,6 +3328,9 @@ impl<'hir> Ty<'hir, AmbigArg> {
     /// In practice this may mean overriding the [`Visitor::visit_infer`][visit_infer] method on hir visitors, or
     /// specifically matching on [`GenericArg::Infer`] when handling generic arguments.
     ///
+    /// For an explanation of what it means for a type to be ambig or unambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
+    ///
     /// [visit_infer]: [rustc_hir::intravisit::Visitor::visit_infer]
     pub fn as_unambig_ty(&self) -> &Ty<'hir> {
         // SAFETY: `Ty` is `repr(C)` and `TyKind` is marked `repr(u8)` so that the layout is
@@ -3338,6 +3346,9 @@ impl<'hir> Ty<'hir> {
     ///
     /// Functions accepting ambiguous types will not handle the [`TyKind::Infer`] variant, if
     /// infer types are relevant to you then care should be taken to handle them separately.
+    ///
+    /// For an explanation of what it means for a type to be ambig or unambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
     pub fn try_as_ambig_ty(&self) -> Option<&Ty<'hir, AmbigArg>> {
         if let TyKind::Infer(()) = self.kind {
             return None;
@@ -3640,9 +3651,12 @@ pub enum InferDelegationKind {
 }
 
 /// The various kinds of types recognized by the compiler.
-#[derive(Debug, Clone, Copy, HashStable_Generic)]
+///
+/// For an explanation of the `Unambig` generic parameter see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
 // SAFETY: `repr(u8)` is required so that `TyKind<()>` and `TyKind<!>` are layout compatible
 #[repr(u8, C)]
+#[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub enum TyKind<'hir, Unambig = ()> {
     /// Actual type should be inherited from `DefId` signature
     InferDelegation(DefId, InferDelegationKind),

compiler/rustc_hir/src/intravisit.rs

@@ -364,8 +364,8 @@ pub trait Visitor<'v>: Sized {
     /// All types are treated as ambiguous types for the purposes of hir visiting in
     /// order to ensure that visitors can handle infer vars without it being too error-prone.
     ///
-    /// See the doc comments on [`Ty`] for an explanation of what it means for a type to be
-    /// ambiguous.
+    /// For an explanation of what it means for a type to be ambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
     ///
     /// The [`Visitor::visit_infer`] method should be overridden in order to handle infer vars.
     fn visit_ty(&mut self, t: &'v Ty<'v, AmbigArg>) -> Self::Result {
@@ -375,12 +375,12 @@ pub trait Visitor<'v>: Sized {
     /// All consts are treated as ambiguous consts for the purposes of hir visiting in
     /// order to ensure that visitors can handle infer vars without it being too error-prone.
     ///
-    /// See the doc comments on [`ConstArg`] for an explanation of what it means for a const to be
-    /// ambiguous.
+    /// For an explanation of what it means for a const arg to be ambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
     ///
     /// The [`Visitor::visit_infer`] method should be overridden in order to handle infer vars.
     fn visit_const_arg(&mut self, c: &'v ConstArg<'v, AmbigArg>) -> Self::Result {
-        walk_ambig_const_arg(self, c)
+        walk_const_arg(self, c)
     }
 
     #[allow(unused_variables)]
@@ -516,6 +516,9 @@ pub trait VisitorExt<'v>: Visitor<'v> {
     ///
     /// Named `visit_ty_unambig` instead of `visit_unambig_ty` to aid in discovery
     /// by IDes when `v.visit_ty` is written.
+    ///
+    /// For an explanation of what it means for a type to be unambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
     fn visit_ty_unambig(&mut self, t: &'v Ty<'v>) -> Self::Result {
         walk_unambig_ty(self, t)
     }
@@ -524,8 +527,11 @@ pub trait VisitorExt<'v>: Visitor<'v> {
     ///
     /// Named `visit_const_arg_unambig` instead of `visit_unambig_const_arg` to aid in
     /// discovery by IDes when `v.visit_const_arg` is written.
+    ///
+    /// For an explanation of what it means for a const arg to be unambig, see the dev-guide:
+    /// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
     fn visit_const_arg_unambig(&mut self, c: &'v ConstArg<'v>) -> Self::Result {
-        walk_const_arg(self, c)
+        walk_unambig_const_arg(self, c)
     }
 }
 impl<'v, V: Visitor<'v>> VisitorExt<'v> for V {}
@@ -975,17 +981,20 @@ pub fn walk_generic_arg<'v, V: Visitor<'v>>(
     }
 }
 
+/// For an explanation of what it means for a type to be unambig, see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
 pub fn walk_unambig_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) -> V::Result {
     match typ.try_as_ambig_ty() {
         Some(ambig_ty) => visitor.visit_ty(ambig_ty),
         None => {
             let Ty { hir_id, span, kind: _ } = typ;
-            try_visit!(visitor.visit_id(*hir_id));
             visitor.visit_infer(*hir_id, *span, InferKind::Ty(typ))
         }
     }
 }
 
+/// For an explanation of what it means for a type to be ambig, see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
 pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v, AmbigArg>) -> V::Result {
     let Ty { hir_id, span: _, kind } = typ;
     try_visit!(visitor.visit_id(*hir_id));
@@ -1038,21 +1047,24 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v, AmbigArg>) -
     V::Result::output()
 }
 
-pub fn walk_const_arg<'v, V: Visitor<'v>>(
+/// For an explanation of what it means for a const arg to be unambig, see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
+pub fn walk_unambig_const_arg<'v, V: Visitor<'v>>(
     visitor: &mut V,
     const_arg: &'v ConstArg<'v>,
 ) -> V::Result {
     match const_arg.try_as_ambig_ct() {
         Some(ambig_ct) => visitor.visit_const_arg(ambig_ct),
         None => {
             let ConstArg { hir_id, kind: _ } = const_arg;
-            try_visit!(visitor.visit_id(*hir_id));
             visitor.visit_infer(*hir_id, const_arg.span(), InferKind::Const(const_arg))
         }
     }
 }
 
-pub fn walk_ambig_const_arg<'v, V: Visitor<'v>>(
+/// For an explanation of what it means for a const arg to be ambig, see the dev-guide:
+/// https://rustc-dev-guide.rust-lang.org/hir/ambig-unambig-ty-and-consts.html
+pub fn walk_const_arg<'v, V: Visitor<'v>>(
     visitor: &mut V,
     const_arg: &'v ConstArg<'v, AmbigArg>,
 ) -> V::Result {