Rollup merge of #120999 - fmease:rustdoc-rm-instantiation-param, r=notriddle

rustdoc: replace `clean::InstantiationParam` with `clean::GenericArg`

Probably better known as `SubstParam` (until #120958 which should've probably renamed it to `InstantiatedParam` but anyways).

It doesn't make any sense to me why it should exist as a separate type. `GenericArg` is exactly what we want here anyways from a semantic perspective. Both have the same size btw.

I also took the liberty of doing some drive-by cleanups.

src/librustdoc/clean/mod.rs

@@ -254,16 +254,14 @@ fn clean_poly_trait_ref_with_bindings<'tcx>(
 }
 
 fn clean_lifetime<'tcx>(lifetime: &hir::Lifetime, cx: &mut DocContext<'tcx>) -> Lifetime {
-    let def = cx.tcx.named_bound_var(lifetime.hir_id);
     if let Some(
-        rbv::ResolvedArg::EarlyBound(node_id)
+        rbv::ResolvedArg::EarlyBound(did)
-        | rbv::ResolvedArg::LateBound(_, _, node_id)
+        | rbv::ResolvedArg::LateBound(_, _, did)
-        | rbv::ResolvedArg::Free(_, node_id),
+        | rbv::ResolvedArg::Free(_, did),
-    ) = def
+    ) = cx.tcx.named_bound_var(lifetime.hir_id)
+        && let Some(lt) = cx.args.get(&did).and_then(|arg| arg.as_lt())
     {
-        if let Some(lt) = cx.args.get(&node_id).and_then(|p| p.as_lt()).cloned() {
+        return lt.clone();
-            return lt;
-        }
     }
     Lifetime(lifetime.ident.name)
 }
@@ -1791,12 +1789,12 @@ fn maybe_expand_private_type_alias<'tcx>(
                     _ => None,
                 });
                 if let Some(lt) = lifetime {
-                    let cleaned = if !lt.is_anonymous() {
+                    let lt = if !lt.is_anonymous() {
                         clean_lifetime(lt, cx)
                     } else {
                         Lifetime::elided()
                     };
-                    args.insert(param.def_id.to_def_id(), InstantiationParam::Lifetime(cleaned));
+                    args.insert(param.def_id.to_def_id(), GenericArg::Lifetime(lt));
                 }
                 indices.lifetimes += 1;
             }
@@ -1805,44 +1803,20 @@ fn maybe_expand_private_type_alias<'tcx>(
                 let type_ = generic_args.args.iter().find_map(|arg| match arg {
                     hir::GenericArg::Type(ty) => {
                         if indices.types == j {
-                            return Some(ty);
+                            return Some(*ty);
                         }
                         j += 1;
                         None
                     }
                     _ => None,
                 });
-                if let Some(ty) = type_ {
+                if let Some(ty) = type_.or(*default) {
-                    args.insert(
+                    args.insert(param.def_id.to_def_id(), GenericArg::Type(clean_ty(ty, cx)));
-                        param.def_id.to_def_id(),
-                        InstantiationParam::Type(clean_ty(ty, cx)),
-                    );
-                } else if let Some(default) = *default {
-                    args.insert(
-                        param.def_id.to_def_id(),
-                        InstantiationParam::Type(clean_ty(default, cx)),
-                    );
                 }
                 indices.types += 1;
             }
-            hir::GenericParamKind::Const { .. } => {
+            // FIXME(#82852): Instantiate const parameters.
-                let mut j = 0;
+            hir::GenericParamKind::Const { .. } => {}
-                let const_ = generic_args.args.iter().find_map(|arg| match arg {
-                    hir::GenericArg::Const(ct) => {
-                        if indices.consts == j {
-                            return Some(ct);
-                        }
-                        j += 1;
-                        None
-                    }
-                    _ => None,
-                });
-                if let Some(_) = const_ {
-                    args.insert(param.def_id.to_def_id(), InstantiationParam::Constant);
-                }
-                // FIXME(const_generics_defaults)
-                indices.consts += 1;
-            }
         }
     }
 

src/librustdoc/clean/types.rs

@@ -2228,6 +2228,16 @@ pub(crate) enum GenericArg {
     Infer,
 }
 
+impl GenericArg {
+    pub(crate) fn as_lt(&self) -> Option<&Lifetime> {
+        if let Self::Lifetime(lt) = self { Some(lt) } else { None }
+    }
+
+    pub(crate) fn as_ty(&self) -> Option<&Type> {
+        if let Self::Type(ty) = self { Some(ty) } else { None }
+    }
+}
+
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub(crate) enum GenericArgs {
     AngleBracketed { args: Box<[GenericArg]>, bindings: ThinVec<TypeBinding> },
@@ -2530,35 +2540,6 @@ pub(crate) enum TypeBindingKind {
     Constraint { bounds: Vec<GenericBound> },
 }
 
-/// The type, lifetime, or constant that a private type alias's parameter should be
-/// replaced with when expanding a use of that type alias.
-///
-/// For example:
-///
-/// ```
-/// type PrivAlias<T> = Vec<T>;
-///
-/// pub fn public_fn() -> PrivAlias<i32> { vec![] }
-/// ```
-///
-/// `public_fn`'s docs will show it as returning `Vec<i32>`, since `PrivAlias` is private.
-/// [`InstantiationParam`] is used to record that `T` should be mapped to `i32`.
-pub(crate) enum InstantiationParam {
-    Type(Type),
-    Lifetime(Lifetime),
-    Constant,
-}
-
-impl InstantiationParam {
-    pub(crate) fn as_ty(&self) -> Option<&Type> {
-        if let Self::Type(ty) = self { Some(ty) } else { None }
-    }
-
-    pub(crate) fn as_lt(&self) -> Option<&Lifetime> {
-        if let Self::Lifetime(lt) = self { Some(lt) } else { None }
-    }
-}
-
 // Some nodes are used a lot. Make sure they don't unintentionally get bigger.
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 mod size_asserts {

src/librustdoc/core.rs

@@ -44,10 +44,13 @@ pub(crate) struct DocContext<'tcx> {
     /// Used while populating `external_traits` to ensure we don't process the same trait twice at
     /// the same time.
     pub(crate) active_extern_traits: DefIdSet,
-    // The current set of parameter instantiations,
+    /// The current set of parameter instantiations for expanding type aliases at the HIR level.
-    // for expanding type aliases at the HIR level:
+    ///
-    /// Table `DefId` of type, lifetime, or const parameter -> instantiated type, lifetime, or const
+    /// Maps from the `DefId` of a lifetime or type parameter to the
-    pub(crate) args: DefIdMap<clean::InstantiationParam>,
+    /// generic argument it's currently instantiated to in this context.
+    // FIXME(#82852): We don't record const params since we don't visit const exprs at all and
+    // therefore wouldn't use the corresp. generic arg anyway. Add support for them.
+    pub(crate) args: DefIdMap<clean::GenericArg>,
     pub(crate) current_type_aliases: DefIdMap<usize>,
     /// Table synthetic type parameter for `impl Trait` in argument position -> bounds
     pub(crate) impl_trait_bounds: FxHashMap<ImplTraitParam, Vec<clean::GenericBound>>,
@@ -87,7 +90,7 @@ impl<'tcx> DocContext<'tcx> {
     /// the generic parameters for a type alias' RHS.
     pub(crate) fn enter_alias<F, R>(
         &mut self,
-        args: DefIdMap<clean::InstantiationParam>,
+        args: DefIdMap<clean::GenericArg>,
         def_id: DefId,
         f: F,
     ) -> R