Auto merge of #93938 - BoxyUwU:fix_res_self_ty, r=lcnr

Make `Res::SelfTy` a struct variant and update docs

I found pattern matching on a `(Option<DefId>, Option<(DefId, bool)>)` to not be super readable, additionally the doc comments on the types in a tuple variant aren't visible anywhere at use sites as far as I can tell (using rust analyzer + vscode)

The docs incorrectly assumed that the `DefId` in `Option<(DefId, bool)>` would only ever be for an impl item and I also found the code examples to be somewhat unclear about which `DefId` was being talked about.

r? `@lcnr` since you reviewed the last PR changing these docs

Author: bors

compiler/rustc_hir/src/def.rs

@@ -266,59 +266,67 @@ pub enum Res<Id = hir::HirId> {
     ///
     /// **Belongs to the type namespace.**
     PrimTy(hir::PrimTy),
-    /// The `Self` type, optionally with the trait it is associated with
-    /// and optionally with the [`DefId`] of the impl it is associated with.
+    /// The `Self` type, optionally with the [`DefId`] of the trait it belongs to and
+    /// optionally with the [`DefId`] of the item introducing the `Self` type alias.
     ///
     /// **Belongs to the type namespace.**
     ///
-    /// For example, the `Self` in
-    ///
+    /// Examples:
     /// ```
+    /// struct Bar(Box<Self>);
+    /// // `Res::SelfTy { trait_: None, alias_of: Some(Bar) }`
+    ///
     /// trait Foo {
     ///     fn foo() -> Box<Self>;
+    ///     // `Res::SelfTy { trait_: Some(Foo), alias_of: None }`
     /// }
-    /// ```
-    ///
-    /// would have the [`DefId`] of `Foo` associated with it. The `Self` in
-    ///
-    /// ```
-    /// struct Bar;
     ///
     /// impl Bar {
-    ///     fn new() -> Self { Bar }
+    ///     fn blah() {
+    ///         let _: Self;
+    ///         // `Res::SelfTy { trait_: None, alias_of: Some(::{impl#0}) }`
+    ///     }
     /// }
-    /// ```
-    ///
-    /// would have the [`DefId`] of the impl associated with it. Finally, the `Self` in
     ///
-    /// ```
     /// impl Foo for Bar {
-    ///     fn foo() -> Box<Self> { Box::new(Bar) }
+    ///     fn foo() -> Box<Self> {
+    ///     // `Res::SelfTy { trait_: Some(Foo), alias_of: Some(::{impl#1}) }`
+    ///         let _: Self;
+    ///         // `Res::SelfTy { trait_: Some(Foo), alias_of: Some(::{impl#1}) }`
+    ///
+    ///         todo!()
+    ///     }
     /// }
     /// ```
     ///
-    /// would have both the [`DefId`] of `Foo` and the [`DefId`] of the impl
-    /// associated with it.
-    ///
     /// *See also [`Res::SelfCtor`].*
     ///
     /// -----
     ///
-    /// HACK(min_const_generics): impl self types also have an optional requirement to **not** mention
+    /// HACK(min_const_generics): self types also have an optional requirement to **not** mention
     /// any generic parameters to allow the following with `min_const_generics`:
     /// ```
     /// impl Foo { fn test() -> [u8; std::mem::size_of::<Self>()] { todo!() } }
+    ///
+    /// struct Bar([u8; baz::<Self>()]);
+    /// const fn baz<T>() -> usize { 10 }
     /// ```
     /// We do however allow `Self` in repeat expression even if it is generic to not break code
-    /// which already works on stable while causing the `const_evaluatable_unchecked` future compat lint.
-    ///
-    /// FIXME(generic_const_exprs): Remove this bodge once that feature is stable.
-    SelfTy(
-        /// Optionally, the trait associated with this `Self` type.
-        Option<DefId>,
-        /// Optionally, the impl associated with this `Self` type.
-        Option<(DefId, bool)>,
-    ),
+    /// which already works on stable while causing the `const_evaluatable_unchecked` future compat lint:
+    /// ```
+    /// fn foo<T>() {
+    ///     let _bar = [1_u8; std::mem::size_of::<*mut T>()];
+    /// }
+    /// ```
+    // FIXME(generic_const_exprs): Remove this bodge once that feature is stable.
+    SelfTy {
+        /// The trait this `Self` is a generic arg for.
+        trait_: Option<DefId>,
+        /// The item introducing the `Self` type alias. Can be used in the `type_of` query
+        /// to get the underlying type. Additionally whether the `Self` type is disallowed
+        /// from mentioning generics (i.e. when used in an anonymous constant).
+        alias_to: Option<(DefId, bool)>,
+    },
     /// A tool attribute module; e.g., the `rustfmt` in `#[rustfmt::skip]`.
     ///
     /// **Belongs to the type namespace.**
@@ -550,7 +558,7 @@ impl<Id> Res<Id> {
 
             Res::Local(..)
             | Res::PrimTy(..)
-            | Res::SelfTy(..)
+            | Res::SelfTy { .. }
             | Res::SelfCtor(..)
             | Res::ToolMod
             | Res::NonMacroAttr(..)
@@ -573,7 +581,7 @@ impl<Id> Res<Id> {
             Res::SelfCtor(..) => "self constructor",
             Res::PrimTy(..) => "builtin type",
             Res::Local(..) => "local variable",
-            Res::SelfTy(..) => "self type",
+            Res::SelfTy { .. } => "self type",
             Res::ToolMod => "tool module",
             Res::NonMacroAttr(attr_kind) => attr_kind.descr(),
             Res::Err => "unresolved item",
@@ -596,7 +604,7 @@ impl<Id> Res<Id> {
             Res::SelfCtor(id) => Res::SelfCtor(id),
             Res::PrimTy(id) => Res::PrimTy(id),
             Res::Local(id) => Res::Local(map(id)),
-            Res::SelfTy(a, b) => Res::SelfTy(a, b),
+            Res::SelfTy { trait_, alias_to } => Res::SelfTy { trait_, alias_to },
             Res::ToolMod => Res::ToolMod,
             Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
             Res::Err => Res::Err,
@@ -620,7 +628,7 @@ impl<Id> Res<Id> {
     pub fn ns(&self) -> Option<Namespace> {
         match self {
             Res::Def(kind, ..) => kind.ns(),
-            Res::PrimTy(..) | Res::SelfTy(..) | Res::ToolMod => Some(Namespace::TypeNS),
+            Res::PrimTy(..) | Res::SelfTy { .. } | Res::ToolMod => Some(Namespace::TypeNS),
             Res::SelfCtor(..) | Res::Local(..) => Some(Namespace::ValueNS),
             Res::NonMacroAttr(..) => Some(Namespace::MacroNS),
             Res::Err => None,

compiler/rustc_hir/src/hir.rs

@@ -640,9 +640,8 @@ impl<'hir> WhereBoundPredicate<'hir> {
             _ => return false,
         };
         match path.res {
-            Res::Def(DefKind::TyParam, def_id) | Res::SelfTy(Some(def_id), None) => {
-                def_id == param_def_id
-            }
+            Res::Def(DefKind::TyParam, def_id)
+            | Res::SelfTy { trait_: Some(def_id), alias_to: None } => def_id == param_def_id,
             _ => false,
         }
     }

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs

@@ -203,7 +203,8 @@ impl<'tcx> Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
                         .map(|res| {
                             matches!(
                                 res,
-                                Res::SelfTy(_, _) | Res::Def(hir::def::DefKind::TyParam, _)
+                                Res::SelfTy { trait_: _, alias_to: _ }
+                                    | Res::Def(hir::def::DefKind::TyParam, _)
                             )
                         })
                         .unwrap_or(false) =>

compiler/rustc_lint/src/internal.rs

@@ -202,7 +202,7 @@ fn is_ty_or_ty_ctxt(cx: &LateContext<'_>, ty: &Ty<'_>) -> Option<String> {
                 }
             }
             // Only lint on `&Ty` and `&TyCtxt` if it is used outside of a trait.
-            Res::SelfTy(None, Some((did, _))) => {
+            Res::SelfTy { trait_: None, alias_to: Some((did, _)) } => {
                 if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
                     if let Some(name @ (sym::Ty | sym::TyCtxt)) =
                         cx.tcx.get_diagnostic_name(adt.did)

compiler/rustc_lint/src/pass_by_value.rs

@@ -54,7 +54,7 @@ fn path_for_pass_by_value(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> Option<Stri
                 let path_segment = path.segments.last().unwrap();
                 return Some(format!("{}{}", name, gen_args(cx, path_segment)));
             }
-            Res::SelfTy(None, Some((did, _))) => {
+            Res::SelfTy { trait_: None, alias_to: Some((did, _)) } => {
                 if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
                     if cx.tcx.has_attr(adt.did, sym::rustc_pass_by_value) {
                         return Some(cx.tcx.def_path_str_with_substs(adt.did, substs));

compiler/rustc_middle/src/ty/adt.rs

@@ -395,7 +395,7 @@ impl<'tcx> AdtDef {
             | Res::Def(DefKind::Union, _)
             | Res::Def(DefKind::TyAlias, _)
             | Res::Def(DefKind::AssocTy, _)
-            | Res::SelfTy(..)
+            | Res::SelfTy { .. }
             | Res::SelfCtor(..) => self.non_enum_variant(),
             _ => bug!("unexpected res {:?} in variant_of_res", res),
         }

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -417,7 +417,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                 | DefKind::AssocTy,
                 _,
             )
-            | Res::SelfTy(..)
+            | Res::SelfTy { .. }
             | Res::SelfCtor(..) => PatKind::Leaf { subpatterns },
             _ => {
                 let pattern_error = match res {

compiler/rustc_passes/src/dead.rs

@@ -104,7 +104,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                     self.check_def_id(variant_id);
                 }
             }
-            Res::SelfTy(t, i) => {
+            Res::SelfTy { trait_: t, alias_to: i } => {
                 if let Some(t) = t {
                     self.check_def_id(t);
                 }

compiler/rustc_privacy/src/lib.rs

@@ -1350,7 +1350,7 @@ struct ObsoleteCheckTypeForPrivatenessVisitor<'a, 'b, 'tcx> {
 impl<'a, 'tcx> ObsoleteVisiblePrivateTypesVisitor<'a, 'tcx> {
     fn path_is_private_type(&self, path: &hir::Path<'_>) -> bool {
         let did = match path.res {
-            Res::PrimTy(..) | Res::SelfTy(..) | Res::Err => return false,
+            Res::PrimTy(..) | Res::SelfTy { .. } | Res::Err => return false,
             res => res.def_id(),
         };
 

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -991,7 +991,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 _,
             )
             | Res::Local(..)
-            | Res::SelfTy(..)
+            | Res::SelfTy { .. }
             | Res::SelfCtor(..)
             | Res::Err => bug!("unexpected resolution: {:?}", res),
         }