Make hir::PathSegment::res non-optional.

compiler/rustc_ast_lowering/src/expr.rs

@@ -1776,12 +1776,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         binding: hir::HirId,
         attrs: AttrVec,
     ) -> hir::Expr<'hir> {
+        let res = Res::Local(binding);
         let expr_path = hir::ExprKind::Path(hir::QPath::Resolved(
             None,
             self.arena.alloc(hir::Path {
                 span: self.lower_span(span),
-                res: Res::Local(binding),
+                res,
-                segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
+                segments: arena_vec![self; hir::PathSegment::from_ident(ident, res)],
             }),
         ));
 

compiler/rustc_ast_lowering/src/item.rs

@@ -1431,10 +1431,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
             GenericParamKind::Const { .. } => None,
             GenericParamKind::Type { .. } => {
                 let def_id = self.local_def_id(id).to_def_id();
+                let res = Res::Def(DefKind::TyParam, def_id);
                 let ty_path = self.arena.alloc(hir::Path {
                     span: param_span,
-                    res: Res::Def(DefKind::TyParam, def_id),
+                    res,
-                    segments: self.arena.alloc_from_iter([hir::PathSegment::from_ident(ident)]),
+                    segments: self
+                        .arena
+                        .alloc_from_iter([hir::PathSegment::from_ident(ident, res)]),
                 });
                 let ty_id = self.next_id();
                 let bounded_ty =

compiler/rustc_ast_lowering/src/lib.rs

@@ -1267,7 +1267,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     self.arena.alloc(hir::Path {
                         res,
                         segments: arena_vec![self; hir::PathSegment::from_ident(
-                            Ident::with_dummy_span(kw::SelfUpper)
+                            Ident::with_dummy_span(kw::SelfUpper),
+                            res
                         )],
                         span: self.lower_span(t.span),
                     }),
@@ -2193,12 +2194,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             hir::PredicateOrigin::ImplTrait,
         );
 
+        let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
         let ty = hir::TyKind::Path(hir::QPath::Resolved(
             None,
             self.arena.alloc(hir::Path {
                 span: self.lower_span(span),
-                res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
+                res,
-                segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident))],
+                segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident), res)],
             }),
         ));
 

compiler/rustc_ast_lowering/src/pat.rs

@@ -254,14 +254,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     lower_sub(self),
                 )
             }
-            Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
+            Some(res) => {
-                None,
+                let res = self.lower_res(res);
-                self.arena.alloc(hir::Path {
+                hir::PatKind::Path(hir::QPath::Resolved(
-                    span: self.lower_span(ident.span),
+                    None,
-                    res: self.lower_res(res),
+                    self.arena.alloc(hir::Path {
-                    segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident))],
+                        span: self.lower_span(ident.span),
-                }),
+                        res,
-            )),
+                        segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident), res)],
+                    }),
+            ))
+            }
         }
     }
 

compiler/rustc_ast_lowering/src/path.rs

@@ -259,7 +259,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         hir::PathSegment {
             ident: self.lower_ident(segment.ident),
             hir_id: Some(id),
-            res: Some(self.lower_res(res)),
+            res: self.lower_res(res),
             infer_args,
             args: if generic_args.is_empty() && generic_args.span.is_empty() {
                 None

compiler/rustc_hir/src/hir.rs

@@ -202,13 +202,10 @@ impl Path<'_> {
 pub struct PathSegment<'hir> {
     /// The identifier portion of this path segment.
     pub ident: Ident,
-    // `id` and `res` are optional. We currently only use these in save-analysis,
+
-    // any path segments without these will not have save-analysis info and
-    // therefore will not have 'jump to def' in IDEs, but otherwise will not be
-    // affected. (In general, we don't bother to get the defs for synthesized
-    // segments, only for segments which have come from the AST).
     pub hir_id: Option<HirId>,
-    pub res: Option<Res>,
+
+    pub res: Res,
 
     /// Type/lifetime parameters attached to this path. They come in
     /// two flavors: `Path<A,B,C>` and `Path(A,B) -> C`. Note that
@@ -226,12 +223,12 @@ pub struct PathSegment<'hir> {
 
 impl<'hir> PathSegment<'hir> {
     /// Converts an identifier to the corresponding segment.
-    pub fn from_ident(ident: Ident) -> PathSegment<'hir> {
+    pub fn from_ident(ident: Ident, res: Res) -> PathSegment<'hir> {
-        PathSegment { ident, hir_id: None, res: None, infer_args: true, args: None }
+        PathSegment { ident, hir_id: None, res, infer_args: true, args: None }
     }
 
     pub fn invalid() -> Self {
-        Self::from_ident(Ident::empty())
+        Self::from_ident(Ident::empty(), Res::Err)
     }
 
     pub fn args(&self) -> &GenericArgs<'hir> {

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -957,7 +957,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
         path.segments
             .iter()
             .filter_map(move |segment| {
-                let res = segment.res?;
+                let res = segment.res;
                 let generics_def_id = tcx.res_generics_def_id(res)?;
                 let generics = tcx.generics_of(generics_def_id);
                 if generics.has_impl_trait() {

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

@@ -154,16 +154,11 @@ impl<'tcx> Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
             }
             hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
                 [segment]
-                    if segment
+                    if matches!(
-                        .res
+                        segment.res,
-                        .map(|res| {
+                        Res::SelfTy { trait_: _, alias_to: _ }
-                            matches!(
+                            | Res::Def(hir::def::DefKind::TyParam, _)
-                                res,
+                    ) =>
-                                Res::SelfTy { trait_: _, alias_to: _ }
-                                    | Res::Def(hir::def::DefKind::TyParam, _)
-                            )
-                        })
-                        .unwrap_or(false) =>
                 {
                     self.types.push(path.span);
                 }

compiler/rustc_lint/src/internal.rs

@@ -118,8 +118,7 @@ impl<'tcx> LateLintPass<'tcx> for TyTyKind {
         _: rustc_hir::HirId,
     ) {
         if let Some(segment) = path.segments.iter().nth_back(1)
-        && let Some(res) = &segment.res
+        && lint_ty_kind_usage(cx, &segment.res)
-        && lint_ty_kind_usage(cx, res)
         {
             let span = path.span.with_hi(
                 segment.args.map_or(segment.ident.span, |a| a.span_ext).hi()

compiler/rustc_passes/src/stability.rs

@@ -832,7 +832,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                 // added, such as `core::intrinsics::transmute`
                 let parents = path.segments.iter().rev().skip(1);
                 for path_segment in parents {
-                    if let Some(def_id) = path_segment.res.as_ref().and_then(Res::opt_def_id) {
+                    if let Some(def_id) = path_segment.res.opt_def_id() {
                         // use `None` for id to prevent deprecation check
                         self.tcx.check_stability_allow_unstable(
                             def_id,

compiler/rustc_save_analysis/src/dump_visitor.rs

@@ -912,7 +912,7 @@ impl<'tcx> DumpVisitor<'tcx> {
                     _,
                 )
                 | Res::SelfTy { .. } => {
-                    self.dump_path_segment_ref(id, &hir::PathSegment::from_ident(ident));
+                    self.dump_path_segment_ref(id, &hir::PathSegment::from_ident(ident, Res::Err));
                 }
                 def => {
                     error!("unexpected definition kind when processing collected idents: {:?}", def)

compiler/rustc_save_analysis/src/lib.rs

@@ -596,13 +596,14 @@ impl<'tcx> SaveContext<'tcx> {
             Node::TraitRef(tr) => tr.path.res,
 
             Node::Item(&hir::Item { kind: hir::ItemKind::Use(path, _), .. }) => path.res,
-            Node::PathSegment(seg) => match seg.res {
+            Node::PathSegment(seg) => {
-                Some(res) if res != Res::Err => res,
+                if seg.res != Res::Err {
-                _ => {
+                    seg.res
+                } else {
                     let parent_node = self.tcx.hir().get_parent_node(hir_id);
                     self.get_path_res(parent_node)
                 }
-            },
+            }
 
             Node::Expr(&hir::Expr { kind: hir::ExprKind::Struct(ref qpath, ..), .. }) => {
                 self.typeck_results().qpath_res(qpath, hir_id)

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -2210,12 +2210,12 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                         && let [
                             ..,
                             trait_path_segment @ hir::PathSegment {
-                                res: Some(rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id)),
+                                res: rustc_hir::def::Res::Def(rustc_hir::def::DefKind::Trait, trait_id),
                                 ..
                             },
                             hir::PathSegment {
                                 ident: assoc_item_name,
-                                res: Some(rustc_hir::def::Res::Def(_, item_id)),
+                                res: rustc_hir::def::Res::Def(_, item_id),
                                 ..
                             }
                         ] = path.segments

compiler/rustc_typeck/src/astconv/mod.rs

@@ -1114,7 +1114,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             let item_segment = hir::PathSegment {
                 ident,
                 hir_id: Some(binding.hir_id),
-                res: None,
+                res: Res::Err,
                 args: Some(binding.gen_args),
                 infer_args: false,
             };
@@ -1845,7 +1845,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                     [.., hir::PathSegment {
                                         ident,
                                         args,
-                                        res: Some(Res::Def(DefKind::Enum, _)),
+                                        res: Res::Def(DefKind::Enum, _),
                                         ..
                                     }, _] => (
                                         // We need to include the `::` in `Type::Variant::<Args>`
@@ -2127,24 +2127,22 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             let types_and_spans: Vec<_> = segments
                 .clone()
                 .flat_map(|segment| {
-                    segment.res.and_then(|res| {
+                    if segment.args().args.is_empty() {
-                        if segment.args().args.is_empty() {
+                        None
-                            None
+                    } else {
-                        } else {
+                        Some((
-                            Some((
+                            match segment.res {
-                            match res {
+                                Res::PrimTy(ty) => format!("{} `{}`", segment.res.descr(), ty.name()),
-                                Res::PrimTy(ty) => format!("{} `{}`", res.descr(), ty.name()),
                                 Res::Def(_, def_id)
                                 if let Some(name) = self.tcx().opt_item_name(def_id) => {
-                                    format!("{} `{name}`", res.descr())
+                                    format!("{} `{name}`", segment.res.descr())
                                 }
                                 Res::Err => "this type".to_string(),
-                                _ => res.descr().to_string(),
+                                _ => segment.res.descr().to_string(),
                             },
                             segment.ident.span,
                         ))
-                        }
+                    }
-                    })
                 })
                 .collect();
             let this_type = match &types_and_spans[..] {

compiler/rustc_typeck/src/check/check.rs

@@ -610,12 +610,7 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
         fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
             match arg.kind {
                 hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
-                    [
+                    [PathSegment { res: Res::SelfTy { trait_: _, alias_to: impl_ref }, .. }] => {
-                        PathSegment {
-                            res: Some(Res::SelfTy { trait_: _, alias_to: impl_ref }),
-                            ..
-                        },
-                    ] => {
                         let impl_ty_name =
                             impl_ref.map(|(def_id, _)| self.tcx.def_path_str(def_id));
                         self.selftys.push((path.span, impl_ty_name));

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -768,7 +768,7 @@ impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
 fn could_be_self(trait_def_id: LocalDefId, ty: &hir::Ty<'_>) -> bool {
     match ty.kind {
         hir::TyKind::TraitObject([trait_ref], ..) => match trait_ref.trait_ref.path.segments {
-            [s] => s.res.and_then(|r| r.opt_def_id()) == Some(trait_def_id.to_def_id()),
+            [s] => s.res.opt_def_id() == Some(trait_def_id.to_def_id()),
             _ => false,
         },
         _ => false,

compiler/rustc_typeck/src/collect/type_of.rs

@@ -1,6 +1,5 @@
 use rustc_errors::{Applicability, StashKey};
 use rustc_hir as hir;
-use rustc_hir::def::Res;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit;
 use rustc_hir::intravisit::Visitor;
@@ -179,15 +178,12 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                 return None;
             };
 
-            // Try to use the segment resolution if it is valid, otherwise we
+            let generics = match tcx.res_generics_def_id(segment.res) {
-            // default to the path resolution.
-            let res = segment.res.filter(|&r| r != Res::Err).unwrap_or(path.res);
-            let generics = match tcx.res_generics_def_id(res) {
                 Some(def_id) => tcx.generics_of(def_id),
                 None => {
                     tcx.sess.delay_span_bug(
                         tcx.def_span(def_id),
-                        &format!("unexpected anon const res {:?} in path: {:?}", res, path),
+                        &format!("unexpected anon const res {:?} in path: {:?}", segment.res, path),
                     );
                     return None;
                 }

src/tools/clippy/clippy_lints/src/operators/op_ref.rs

@@ -185,7 +185,7 @@ fn in_impl<'tcx>(
         if let ItemKind::Impl(item) = &item.kind;
         if let Some(of_trait) = &item.of_trait;
         if let Some(seg) = of_trait.path.segments.last();
-        if let Some(Res::Def(_, trait_id)) = seg.res;
+        if let Res::Def(_, trait_id) = seg.res;
         if trait_id == bin_op;
         if let Some(generic_args) = seg.args;
         if let Some(GenericArg::Type(other_ty)) = generic_args.args.last();

src/tools/clippy/clippy_lints/src/ref_option_ref.rs

@@ -43,8 +43,7 @@ impl<'tcx> LateLintPass<'tcx> for RefOptionRef {
             if mut_ty.mutbl == Mutability::Not;
             if let TyKind::Path(ref qpath) = &mut_ty.ty.kind;
             let last = last_path_segment(qpath);
-            if let Some(res) = last.res;
+            if let Some(def_id) = last.res.opt_def_id();
-            if let Some(def_id) = res.opt_def_id();
 
             if cx.tcx.is_diagnostic_item(sym::Option, def_id);
             if let Some(params) = last_path_segment(qpath).args ;

src/tools/clippy/clippy_lints/src/trait_bounds.rs

@@ -128,7 +128,7 @@ impl<'tcx> LateLintPass<'tcx> for TraitBounds {
                 if !bound_predicate.span.from_expansion();
                 if let TyKind::Path(QPath::Resolved(_, Path { segments, .. })) = bound_predicate.bounded_ty.kind;
                 if let Some(PathSegment {
-                    res: Some(Res::SelfTy{ trait_: Some(def_id), alias_to: _ }), ..
+                    res: Res::SelfTy{ trait_: Some(def_id), alias_to: _ }, ..
                 }) = segments.first();
                 if let Some(
                     Node::Item(