Introduce DefPathData::AnonAssocTy.

PR rust-lang#137977 changed `DefPathData::TypeNs` to contain `Option<Symbol>` to
account for RPITIT assoc types being anonymous. This commit changes it
back to `Symbol` and gives anonymous assoc types their own variant. It
makes things a bit nicer overall.

Author: nnethercote

Diff for: compiler/rustc_hir/src/def.rs

@@ -267,11 +267,16 @@ impl DefKind {
             | DefKind::ForeignTy
             | DefKind::TraitAlias
             | DefKind::TyParam
-            | DefKind::ExternCrate => DefPathData::TypeNs(Some(name.unwrap())),
-
-            // An associated type names will be missing for an RPITIT. It will
-            // later be given a name with `synthetic` in it, if necessary.
-            DefKind::AssocTy => DefPathData::TypeNs(name),
+            | DefKind::ExternCrate => DefPathData::TypeNs(name.unwrap()),
+
+            // An associated type name will be missing for an RPITIT.
+            DefKind::AssocTy => {
+                if let Some(name) = name {
+                    DefPathData::TypeNs(name)
+                } else {
+                    DefPathData::AnonAssocTy
+                }
+            }
 
             // It's not exactly an anon const, but wrt DefPathData, there
             // is no difference.

Diff for: compiler/rustc_hir/src/definitions.rs

@@ -271,9 +271,8 @@ pub enum DefPathData {
     Use,
     /// A global asm item.
     GlobalAsm,
-    /// Something in the type namespace. Will be empty for RPITIT associated
-    /// types, which are given a synthetic name later, if necessary.
-    TypeNs(Option<Symbol>),
+    /// Something in the type namespace.
+    TypeNs(Symbol),
     /// Something in the value namespace.
     ValueNs(Symbol),
     /// Something in the macro namespace.
@@ -291,6 +290,8 @@ pub enum DefPathData {
     /// An existential `impl Trait` type node.
     /// Argument position `impl Trait` have a `TypeNs` with their pretty-printed name.
     OpaqueTy,
+    /// An anonymous associated type from an RPITIT.
+    AnonAssocTy,
     /// A synthetic body for a coroutine's by-move body.
     SyntheticCoroutineBody,
 }
@@ -413,9 +414,7 @@ impl DefPathData {
     pub fn get_opt_name(&self) -> Option<Symbol> {
         use self::DefPathData::*;
         match *self {
-            TypeNs(name) => name,
-
-            ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
+            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
 
             Impl
             | ForeignMod
@@ -426,21 +425,17 @@ impl DefPathData {
             | Ctor
             | AnonConst
             | OpaqueTy
+            | AnonAssocTy
             | SyntheticCoroutineBody => None,
         }
     }
 
     pub fn name(&self) -> DefPathDataName {
         use self::DefPathData::*;
         match *self {
-            TypeNs(name) => {
-                if let Some(name) = name {
-                    DefPathDataName::Named(name)
-                } else {
-                    DefPathDataName::Anon { namespace: sym::synthetic }
-                }
+            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => {
+                DefPathDataName::Named(name)
             }
-            ValueNs(name) | MacroNs(name) | LifetimeNs(name) => DefPathDataName::Named(name),
             // Note that this does not show up in user print-outs.
             CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
             Impl => DefPathDataName::Anon { namespace: kw::Impl },
@@ -451,6 +446,7 @@ impl DefPathData {
             Ctor => DefPathDataName::Anon { namespace: sym::constructor },
             AnonConst => DefPathDataName::Anon { namespace: sym::constant },
             OpaqueTy => DefPathDataName::Anon { namespace: sym::opaque },
+            AnonAssocTy => DefPathDataName::Anon { namespace: sym::synthetic },
             SyntheticCoroutineBody => DefPathDataName::Anon { namespace: sym::synthetic },
         }
     }

Diff for: compiler/rustc_middle/src/ty/print/pretty.rs

@@ -620,7 +620,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             // the children of the visible parent (as was done when computing
             // `visible_parent_map`), looking for the specific child we currently have and then
             // have access to the re-exported name.
-            DefPathData::TypeNs(Some(ref mut name)) if Some(visible_parent) != actual_parent => {
+            DefPathData::TypeNs(ref mut name) if Some(visible_parent) != actual_parent => {
                 // Item might be re-exported several times, but filter for the one
                 // that's public and whose identifier isn't `_`.
                 let reexport = self
@@ -641,7 +641,7 @@ pub trait PrettyPrinter<'tcx>: Printer<'tcx> + fmt::Write {
             }
             // Re-exported `extern crate` (#43189).
             DefPathData::CrateRoot => {
-                data = DefPathData::TypeNs(Some(self.tcx().crate_name(def_id.krate)));
+                data = DefPathData::TypeNs(self.tcx().crate_name(def_id.krate));
             }
             _ => {}
         }

Diff for: compiler/rustc_middle/src/ty/significant_drop_order.rs

@@ -26,7 +26,7 @@ fn true_significant_drop_ty<'tcx>(
                     name_rev.push(tcx.crate_name(did.krate));
                 }
                 rustc_hir::definitions::DefPathData::TypeNs(symbol) => {
-                    name_rev.push(symbol.unwrap());
+                    name_rev.push(symbol);
                 }
                 _ => return None,
             }

Diff for: compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/encode.rs

@@ -721,7 +721,8 @@ fn encode_ty_name(tcx: TyCtxt<'_>, def_id: DefId) -> String {
             | hir::definitions::DefPathData::Use
             | hir::definitions::DefPathData::GlobalAsm
             | hir::definitions::DefPathData::MacroNs(..)
-            | hir::definitions::DefPathData::LifetimeNs(..) => {
+            | hir::definitions::DefPathData::LifetimeNs(..)
+            | hir::definitions::DefPathData::AnonAssocTy => {
                 bug!("encode_ty_name: unexpected `{:?}`", disambiguated_data.data);
             }
         });

Diff for: compiler/rustc_symbol_mangling/src/v0.rs

@@ -858,7 +858,8 @@ impl<'tcx> Printer<'tcx> for SymbolMangler<'tcx> {
             | DefPathData::GlobalAsm
             | DefPathData::Impl
             | DefPathData::MacroNs(_)
-            | DefPathData::LifetimeNs(_) => {
+            | DefPathData::LifetimeNs(_)
+            | DefPathData::AnonAssocTy => {
                 bug!("symbol_names: unexpected DefPathData: {:?}", disambiguated_data.data)
             }
         };

Diff for: compiler/rustc_ty_utils/src/assoc.rs

@@ -252,7 +252,7 @@ fn associated_type_for_impl_trait_in_trait(
     assert_eq!(tcx.def_kind(trait_def_id), DefKind::Trait);
 
     let span = tcx.def_span(opaque_ty_def_id);
-    // No name because this is a synthetic associated type.
+    // No name because this is an anonymous associated type.
     let trait_assoc_ty = tcx.at(span).create_def(trait_def_id, None, DefKind::AssocTy);
 
     let local_def_id = trait_assoc_ty.def_id();
@@ -305,7 +305,7 @@ fn associated_type_for_impl_trait_in_impl(
         hir::FnRetTy::DefaultReturn(_) => tcx.def_span(impl_fn_def_id),
         hir::FnRetTy::Return(ty) => ty.span,
     };
-    // No name because this is a synthetic associated type.
+    // No name because this is an anonymous associated type.
     let impl_assoc_ty = tcx.at(span).create_def(impl_local_def_id, None, DefKind::AssocTy);
 
     let local_def_id = impl_assoc_ty.def_id();

Diff for: src/tools/clippy/clippy_utils/src/lib.rs

@@ -3502,7 +3502,7 @@ fn maybe_get_relative_path(from: &DefPath, to: &DefPath, max_super: usize) -> St
                 // a::b::c  ::d::sym refers to
                 // e::f::sym:: ::
                 // result should be super::super::super::super::e::f
-                if let DefPathData::TypeNs(Some(s)) = l {
+                if let DefPathData::TypeNs(s) = l {
                     path.push(s.to_string());
                 }
                 if let DefPathData::TypeNs(_) = r {
@@ -3513,7 +3513,7 @@ fn maybe_get_relative_path(from: &DefPath, to: &DefPath, max_super: usize) -> St
             // a::b::sym:: ::    refers to
             // c::d::e  ::f::sym
             // when looking at `f`
-            Left(DefPathData::TypeNs(Some(sym))) => path.push(sym.to_string()),
+            Left(DefPathData::TypeNs(sym)) => path.push(sym.to_string()),
             // consider:
             // a::b::c  ::d::sym refers to
             // e::f::sym:: ::
@@ -3527,7 +3527,7 @@ fn maybe_get_relative_path(from: &DefPath, to: &DefPath, max_super: usize) -> St
         // `super` chain would be too long, just use the absolute path instead
         once(String::from("crate"))
             .chain(to.data.iter().filter_map(|el| {
-                if let DefPathData::TypeNs(Some(sym)) = el.data {
+                if let DefPathData::TypeNs(sym) = el.data {
                     Some(sym.to_string())
                 } else {
                     None