Add const effect syntax to the parser for all function headers

Author: oli-obk

compiler/rustc_ast/src/ast.rs

@@ -3021,7 +3021,7 @@ impl BoundPolarity {
     }
 }
 
-/// The constness of a trait bound.
+/// The constness of a trait bound or function.
 #[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, Hash)]
 #[derive(HashStable_Generic)]
 pub enum BoundConstness {
@@ -3473,7 +3473,7 @@ pub struct FnHeader {
     /// Whether this is `async`, `gen`, or nothing.
     pub coroutine_kind: Option<CoroutineKind>,
     /// The `const` keyword, if any
-    pub constness: Const,
+    pub constness: BoundConstness,
     /// The `extern` keyword and corresponding ABI string, if any.
     pub ext: Extern,
 }
@@ -3484,7 +3484,7 @@ impl FnHeader {
         let Self { safety, coroutine_kind, constness, ext } = self;
         matches!(safety, Safety::Unsafe(_))
             || coroutine_kind.is_some()
-            || matches!(constness, Const::Yes(_))
+            || !matches!(constness, BoundConstness::Never)
             || !matches!(ext, Extern::None)
     }
 }
@@ -3494,7 +3494,7 @@ impl Default for FnHeader {
         FnHeader {
             safety: Safety::Default,
             coroutine_kind: None,
-            constness: Const::No,
+            constness: BoundConstness::Never,
             ext: Extern::None,
         }
     }

compiler/rustc_ast/src/mut_visit.rs

@@ -902,6 +902,14 @@ fn visit_constness<T: MutVisitor>(vis: &mut T, constness: &mut Const) {
     }
 }
 
+// No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
+fn walk_bound_constness<T: MutVisitor>(vis: &mut T, constness: &mut BoundConstness) {
+    match constness {
+        BoundConstness::Never => {}
+        BoundConstness::Always(span) | BoundConstness::Maybe(span) => vis.visit_span(span),
+    }
+}
+
 fn walk_closure_binder<T: MutVisitor>(vis: &mut T, binder: &mut ClosureBinder) {
     match binder {
         ClosureBinder::NotPresent => {}
@@ -1131,10 +1139,7 @@ fn walk_poly_trait_ref<T: MutVisitor>(vis: &mut T, p: &mut PolyTraitRef) {
 
 fn walk_modifiers<V: MutVisitor>(vis: &mut V, m: &mut TraitBoundModifiers) {
     let TraitBoundModifiers { constness, asyncness, polarity } = m;
-    match constness {
-        BoundConstness::Never => {}
-        BoundConstness::Always(span) | BoundConstness::Maybe(span) => vis.visit_span(span),
-    }
+    walk_bound_constness(vis, constness);
     match asyncness {
         BoundAsyncness::Normal => {}
         BoundAsyncness::Async(span) => vis.visit_span(span),
@@ -1443,7 +1448,7 @@ fn walk_const_item<T: MutVisitor>(vis: &mut T, item: &mut ConstItem) {
 
 fn walk_fn_header<T: MutVisitor>(vis: &mut T, header: &mut FnHeader) {
     let FnHeader { safety, coroutine_kind, constness, ext: _ } = header;
-    visit_constness(vis, constness);
+    walk_bound_constness(vis, constness);
     coroutine_kind.as_mut().map(|coroutine_kind| vis.visit_coroutine_kind(coroutine_kind));
     visit_safety(vis, safety);
 }