impl DiscriminantKind for all types

Author: basil-cow

chalk-integration/src/lowering.rs

@@ -1118,6 +1118,7 @@ impl Lower for WellKnownTrait {
             WellKnownTrait::Unsize => rust_ir::WellKnownTrait::Unsize,
             WellKnownTrait::Unpin => rust_ir::WellKnownTrait::Unpin,
             WellKnownTrait::CoerceUnsized => rust_ir::WellKnownTrait::CoerceUnsized,
+            WellKnownTrait::DiscriminantKind => rust_ir::WellKnownTrait::DiscriminantKind,
         }
     }
 }

chalk-parse/src/ast.rs

@@ -141,6 +141,7 @@ pub enum WellKnownTrait {
     Unsize,
     Unpin,
     CoerceUnsized,
+    DiscriminantKind,
 }
 
 #[derive(Clone, PartialEq, Eq, Debug)]

chalk-parse/src/parser.lalrpop

@@ -55,16 +55,21 @@ ObjectSafeKeyword: () = "#" "[" "object_safe" "]";
 PhantomDataKeyword: () = "#" "[" "phantom_data" "]";
 
 WellKnownTrait: WellKnownTrait = {
-     "#" "[" "lang" "(" "sized" ")" "]" => WellKnownTrait::Sized,
-     "#" "[" "lang" "(" "copy" ")" "]" => WellKnownTrait::Copy,
-     "#" "[" "lang" "(" "clone" ")" "]" => WellKnownTrait::Clone,
-     "#" "[" "lang" "(" "drop" ")" "]" => WellKnownTrait::Drop,
-     "#" "[" "lang" "(" "fn_once" ")" "]" => WellKnownTrait::FnOnce,
-     "#" "[" "lang" "(" "fn_mut" ")" "]" => WellKnownTrait::FnMut,
-     "#" "[" "lang" "(" "fn" ")" "]" => WellKnownTrait::Fn,
-     "#" "[" "lang" "(" "unsize" ")" "]" => WellKnownTrait::Unsize,
-     "#" "[" "lang" "(" "unpin" ")" "]" => WellKnownTrait::Unpin, 
-     "#" "[" "lang" "(" "coerce_unsized" ")" "]" => WellKnownTrait::CoerceUnsized,
+    "#" "[" "lang" "(" <n:WellKnownTraitName> ")" "]" => n,
+}
+
+WellKnownTraitName: WellKnownTrait = {
+    "sized" => WellKnownTrait::Sized,
+    "copy" => WellKnownTrait::Copy,
+    "clone" => WellKnownTrait::Clone,
+    "drop" => WellKnownTrait::Drop,
+    "fn_once" => WellKnownTrait::FnOnce,
+    "fn_mut" => WellKnownTrait::FnMut,
+    "fn" => WellKnownTrait::Fn,
+    "unsize" => WellKnownTrait::Unsize,
+    "unpin" => WellKnownTrait::Unpin, 
+    "coerce_unsized" => WellKnownTrait::CoerceUnsized,
+    "discriminant_kind" => WellKnownTrait::DiscriminantKind,
 };
 
 AdtRepr: Atom = "#" "[" "repr" "(" <name:Id> ")" "]" => name.str;

chalk-solve/src/clauses/builtin_traits.rs

@@ -41,6 +41,8 @@ pub fn add_builtin_program_clauses<I: Interner>(
             WellKnownTrait::Unsize => {
                 unsize::add_unsize_program_clauses(db, builder, &trait_ref, ty)
             }
+            // DiscriminantKind is automatically implemented for all types
+            WellKnownTrait::DiscriminantKind => builder.push_fact(trait_ref),
             // There are no builtin impls provided for the following traits:
             WellKnownTrait::Unpin | WellKnownTrait::Drop | WellKnownTrait::CoerceUnsized => (),
         }

chalk-solve/src/display/items.rs

@@ -201,6 +201,7 @@ impl<I: Interner> RenderAsRust<I> for TraitDatum<I> {
                 WellKnownTrait::Unsize => "unsize",
                 WellKnownTrait::Unpin => "unpin",
                 WellKnownTrait::CoerceUnsized => "coerce_unsized",
+                WellKnownTrait::DiscriminantKind => "discriminant_kind",
             };
             writeln!(f, "#[lang({})]", name)?;
         }

chalk-solve/src/rust_ir.rs

@@ -262,6 +262,7 @@ pub enum WellKnownTrait {
     Unsize,
     Unpin,
     CoerceUnsized,
+    DiscriminantKind,
 }
 
 chalk_ir::const_visit!(WellKnownTrait);

chalk-solve/src/wf.rs

@@ -419,7 +419,8 @@ where
             | WellKnownTrait::FnOnce
             | WellKnownTrait::FnMut
             | WellKnownTrait::Unsize
-            | WellKnownTrait::Sized => false,
+            | WellKnownTrait::Sized
+            | WellKnownTrait::DiscriminantKind => false,
         };
 
         if is_legal {