add CoerceUnsized to parser

Author: basil-cow

chalk-integration/src/lowering.rs

@@ -1156,6 +1156,7 @@ impl Lower for WellKnownTrait {
             WellKnownTrait::Fn => rust_ir::WellKnownTrait::Fn,
             WellKnownTrait::Unsize => rust_ir::WellKnownTrait::Unsize,
             WellKnownTrait::Unpin => rust_ir::WellKnownTrait::Unpin,
+            WellKnownTrait::CoerceUnsized => rust_ir::WellKnownTrait::CoerceUnsized,
         }
     }
 }

chalk-parse/src/ast.rs

@@ -127,6 +127,7 @@ pub enum WellKnownTrait {
     Fn,
     Unsize,
     Unpin,
+    CoerceUnsized,
 }
 
 #[derive(Clone, PartialEq, Eq, Debug)]

chalk-parse/src/parser.lalrpop

@@ -63,6 +63,7 @@ WellKnownTrait: WellKnownTrait = {
      "#" "[" "lang" "(" "fn" ")" "]" => WellKnownTrait::Fn,
      "#" "[" "lang" "(" "unsize" ")" "]" => WellKnownTrait::Unsize,
      "#" "[" "lang" "(" "unpin" ")" "]" => WellKnownTrait::Unpin, 
+     "#" "[" "lang" "(" "coerce_unsized" ")" "]" => WellKnownTrait::CoerceUnsized,
 };
 
 AdtRepr: Atom = "#" "[" "repr" "(" <name:Id> ")" "]" => name.str;

chalk-solve/src/clauses/builtin_traits.rs

@@ -41,12 +41,8 @@ pub fn add_builtin_program_clauses<I: Interner>(
             WellKnownTrait::Unsize => {
                 unsize::add_unsize_program_clauses(db, builder, &trait_ref, ty)
             }
-
-            // Drop impls are provided explicitly
-            WellKnownTrait::Drop => (),
-
-            // There are no special rules for Unpin
-            WellKnownTrait::Unpin => (),
+            // There are no builtin impls provided for the following traits:
+            WellKnownTrait::Unpin | WellKnownTrait::Drop | WellKnownTrait::CoerceUnsized => (),
         }
         Ok(())
     })

chalk-solve/src/display/items.rs

@@ -194,6 +194,7 @@ impl<I: Interner> RenderAsRust<I> for TraitDatum<I> {
                 WellKnownTrait::Fn => "fn",
                 WellKnownTrait::Unsize => "unsize",
                 WellKnownTrait::Unpin => "unpin",
+                WellKnownTrait::CoerceUnsized => "coerce_unsized",
             };
             writeln!(f, "#[lang({})]", name)?;
         }

chalk-solve/src/rust_ir.rs

@@ -270,6 +270,7 @@ pub enum WellKnownTrait {
     Fn,
     Unsize,
     Unpin,
+    CoerceUnsized,
 }
 
 chalk_ir::const_visit!(WellKnownTrait);

chalk-solve/src/wf.rs

@@ -338,7 +338,7 @@ where
             WellKnownTrait::Drop => {
                 WfWellKnownConstraints::drop_impl_constraint(&mut *solver, self.db, &impl_datum)
             }
-            WellKnownTrait::Clone | WellKnownTrait::Unpin => true,
+            WellKnownTrait::Clone | WellKnownTrait::Unpin | WellKnownTrait::CoerceUnsized => true,
             // You can't add a manual implementation for the following traits:
             WellKnownTrait::Fn
             | WellKnownTrait::FnOnce