Refactor AST trait bound modifiers

compiler/rustc_ast/src/ast.rs

@@ -286,41 +286,16 @@ impl ParenthesizedArgs {
 
 pub use crate::node_id::{NodeId, CRATE_NODE_ID, DUMMY_NODE_ID};
 
-/// A modifier on a bound, e.g., `?Trait` or `~const Trait`.
-///
-/// Negative bounds should also be handled here.
+/// Modifiers on a trait bound like `~const`, `?` and `!`.
 #[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug)]
-pub enum TraitBoundModifier {
-    /// No modifiers
-    None,
-
-    /// `!Trait`
-    Negative,
-
-    /// `?Trait`
-    Maybe,
-
-    /// `~const Trait`
-    MaybeConst(Span),
-
-    /// `~const !Trait`
-    //
-    // This parses but will be rejected during AST validation.
-    MaybeConstNegative,
-
-    /// `~const ?Trait`
-    //
-    // This parses but will be rejected during AST validation.
-    MaybeConstMaybe,
+pub struct TraitBoundModifiers {
+    pub constness: BoundConstness,
+    pub polarity: BoundPolarity,
 }
 
-impl TraitBoundModifier {
-    pub fn to_constness(self) -> Const {
-        match self {
-            Self::MaybeConst(span) => Const::Yes(span),
-            _ => Const::No,
-        }
-    }
+impl TraitBoundModifiers {
+    pub const NONE: Self =
+        Self { constness: BoundConstness::Never, polarity: BoundPolarity::Positive };
 }
 
 /// The AST represents all type param bounds as types.
@@ -329,7 +304,7 @@ impl TraitBoundModifier {
 /// detects `Copy`, `Send` and `Sync`.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum GenericBound {
-    Trait(PolyTraitRef, TraitBoundModifier),
+    Trait(PolyTraitRef, TraitBoundModifiers),
     Outlives(Lifetime),
 }
 
@@ -1193,7 +1168,7 @@ impl Expr {
         match &self.kind {
             ExprKind::Path(None, path) => Some(GenericBound::Trait(
                 PolyTraitRef::new(ThinVec::new(), path.clone(), self.span),
-                TraitBoundModifier::None,
+                TraitBoundModifiers::NONE,
             )),
             _ => None,
         }
@@ -2491,6 +2466,15 @@ pub enum Const {
     No,
 }
 
+impl From<BoundConstness> for Const {
+    fn from(constness: BoundConstness) -> Self {
+        match constness {
+            BoundConstness::Maybe(span) => Self::Yes(span),
+            BoundConstness::Never => Self::No,
+        }
+    }
+}
+
 /// Item defaultness.
 /// For details see the [RFC #2532](https://github.com/rust-lang/rfcs/pull/2532).
 #[derive(Copy, Clone, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
@@ -2516,7 +2500,9 @@ impl fmt::Debug for ImplPolarity {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Encodable, Decodable, HashStable_Generic)]
+/// The polarity of a trait bound.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug)]
+#[derive(HashStable_Generic)]
 pub enum BoundPolarity {
     /// `Type: Trait`
     Positive,
@@ -2526,6 +2512,35 @@ pub enum BoundPolarity {
     Maybe(Span),
 }
 
+impl BoundPolarity {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Positive => "",
+            Self::Negative(_) => "!",
+            Self::Maybe(_) => "?",
+        }
+    }
+}
+
+/// The constness of a trait bound.
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug)]
+#[derive(HashStable_Generic)]
+pub enum BoundConstness {
+    /// `Type: Trait`
+    Never,
+    /// `Type: ~const Trait`
+    Maybe(Span),
+}
+
+impl BoundConstness {
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Never => "",
+            Self::Maybe(_) => "~const",
+        }
+    }
+}
+
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum FnRetTy {
     /// Returns type is not specified.
@@ -3255,7 +3270,7 @@ mod size_asserts {
     static_assert_size!(ForeignItem, 96);
     static_assert_size!(ForeignItemKind, 24);
     static_assert_size!(GenericArg, 24);
-    static_assert_size!(GenericBound, 64);
+    static_assert_size!(GenericBound, 72);
     static_assert_size!(Generics, 40);
     static_assert_size!(Impl, 136);
     static_assert_size!(Item, 136);