Refactor `where` predicates, and reserve for attributes support

3 files changed, 44 insertions, 31 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 792de77e9d4..5b5ffe11379 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -428,7 +428,15 @@ impl Default for WhereClause {
 
 /// A single predicate in a where-clause.
 #[derive(Clone, Encodable, Decodable, Debug)]
-pub enum WherePredicate {
+pub struct WherePredicate {
+    pub kind: WherePredicateKind,
+    pub id: NodeId,
+    pub span: Span,
+}
+
+/// Predicate kind in where-clause.
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub enum WherePredicateKind {
     /// A type bound (e.g., `for<'c> Foo: Send + Clone + 'c`).
     BoundPredicate(WhereBoundPredicate),
     /// A lifetime predicate (e.g., `'a: 'b + 'c`).
@@ -437,22 +445,11 @@ pub enum WherePredicate {
     EqPredicate(WhereEqPredicate),
 }
 
-impl WherePredicate {
-    pub fn span(&self) -> Span {
-        match self {
-            WherePredicate::BoundPredicate(p) => p.span,
-            WherePredicate::RegionPredicate(p) => p.span,
-            WherePredicate::EqPredicate(p) => p.span,
-        }
-    }
-}
-
 /// A type bound.
 ///
 /// E.g., `for<'c> Foo: Send + Clone + 'c`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WhereBoundPredicate {
-    pub span: Span,
     /// Any generics from a `for` binding.
     pub bound_generic_params: ThinVec<GenericParam>,
     /// The type being bounded.
@@ -466,7 +463,6 @@ pub struct WhereBoundPredicate {
 /// E.g., `'a: 'b + 'c`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WhereRegionPredicate {
-    pub span: Span,
     pub lifetime: Lifetime,
     pub bounds: GenericBounds,
 }
@@ -476,7 +472,6 @@ pub struct WhereRegionPredicate {
 /// E.g., `T = int`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WhereEqPredicate {
-    pub span: Span,
     pub lhs_ty: P<Ty>,
     pub rhs_ty: P<Ty>,
 }
diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 198e1bca774..0aceed45028 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -332,7 +332,11 @@ pub trait MutVisitor: Sized {
     }
 
     fn visit_where_predicate(&mut self, where_predicate: &mut WherePredicate) {
-        walk_where_predicate(self, where_predicate);
+        walk_where_predicate(self, where_predicate)
+    }
+
+    fn visit_where_predicate_kind(&mut self, kind: &mut WherePredicateKind) {
+        walk_where_predicate_kind(self, kind)
     }
 
     fn visit_vis(&mut self, vis: &mut Visibility) {
@@ -1065,26 +1069,30 @@ fn walk_where_clause<T: MutVisitor>(vis: &mut T, wc: &mut WhereClause) {
     vis.visit_span(span);
 }
 
-fn walk_where_predicate<T: MutVisitor>(vis: &mut T, pred: &mut WherePredicate) {
-    match pred {
-        WherePredicate::BoundPredicate(bp) => {
-            let WhereBoundPredicate { span, bound_generic_params, bounded_ty, bounds } = bp;
+pub fn walk_where_predicate<T: MutVisitor>(vis: &mut T, pred: &mut WherePredicate) {
+    let WherePredicate { kind, id, span } = pred;
+    vis.visit_id(id);
+    vis.visit_where_predicate_kind(kind);
+    vis.visit_span(span);
+}
+
+pub fn walk_where_predicate_kind<T: MutVisitor>(vis: &mut T, kind: &mut WherePredicateKind) {
+    match kind {
+        WherePredicateKind::BoundPredicate(bp) => {
+            let WhereBoundPredicate { bound_generic_params, bounded_ty, bounds } = bp;
             bound_generic_params.flat_map_in_place(|param| vis.flat_map_generic_param(param));
             vis.visit_ty(bounded_ty);
             visit_vec(bounds, |bound| vis.visit_param_bound(bound, BoundKind::Bound));
-            vis.visit_span(span);
         }
-        WherePredicate::RegionPredicate(rp) => {
-            let WhereRegionPredicate { span, lifetime, bounds } = rp;
+        WherePredicateKind::RegionPredicate(rp) => {
+            let WhereRegionPredicate { lifetime, bounds } = rp;
             vis.visit_lifetime(lifetime);
             visit_vec(bounds, |bound| vis.visit_param_bound(bound, BoundKind::Bound));
-            vis.visit_span(span);
         }
-        WherePredicate::EqPredicate(ep) => {
-            let WhereEqPredicate { span, lhs_ty, rhs_ty } = ep;
+        WherePredicateKind::EqPredicate(ep) => {
+            let WhereEqPredicate { lhs_ty, rhs_ty } = ep;
             vis.visit_ty(lhs_ty);
             vis.visit_ty(rhs_ty);
-            vis.visit_span(span);
         }
     }
 }
diff --git a/compiler/rustc_ast/src/visit.rs b/compiler/rustc_ast/src/visit.rs
index 20ac9fa02bb..718397e8ca0 100644
--- a/compiler/rustc_ast/src/visit.rs
+++ b/compiler/rustc_ast/src/visit.rs
@@ -192,6 +192,9 @@ pub trait Visitor<'ast>: Sized {
     fn visit_where_predicate(&mut self, p: &'ast WherePredicate) -> Self::Result {
         walk_where_predicate(self, p)
     }
+    fn visit_where_predicate_kind(&mut self, k: &'ast WherePredicateKind) -> Self::Result {
+        walk_where_predicate_kind(self, k)
+    }
     fn visit_fn(&mut self, fk: FnKind<'ast>, _: Span, _: NodeId) -> Self::Result {
         walk_fn(self, fk)
     }
@@ -794,22 +797,29 @@ pub fn walk_where_predicate<'a, V: Visitor<'a>>(
     visitor: &mut V,
     predicate: &'a WherePredicate,
 ) -> V::Result {
-    match predicate {
-        WherePredicate::BoundPredicate(WhereBoundPredicate {
+    let WherePredicate { kind, id: _, span: _ } = predicate;
+    visitor.visit_where_predicate_kind(kind)
+}
+
+pub fn walk_where_predicate_kind<'a, V: Visitor<'a>>(
+    visitor: &mut V,
+    kind: &'a WherePredicateKind,
+) -> V::Result {
+    match kind {
+        WherePredicateKind::BoundPredicate(WhereBoundPredicate {
             bounded_ty,
             bounds,
             bound_generic_params,
-            span: _,
         }) => {
             walk_list!(visitor, visit_generic_param, bound_generic_params);
             try_visit!(visitor.visit_ty(bounded_ty));
             walk_list!(visitor, visit_param_bound, bounds, BoundKind::Bound);
         }
-        WherePredicate::RegionPredicate(WhereRegionPredicate { lifetime, bounds, span: _ }) => {
+        WherePredicateKind::RegionPredicate(WhereRegionPredicate { lifetime, bounds }) => {
             try_visit!(visitor.visit_lifetime(lifetime, LifetimeCtxt::Bound));
             walk_list!(visitor, visit_param_bound, bounds, BoundKind::Bound);
         }
-        WherePredicate::EqPredicate(WhereEqPredicate { lhs_ty, rhs_ty, span: _ }) => {
+        WherePredicateKind::EqPredicate(WhereEqPredicate { lhs_ty, rhs_ty }) => {
             try_visit!(visitor.visit_ty(lhs_ty));
             try_visit!(visitor.visit_ty(rhs_ty));
         }