add unsize builtin impls

Author: basil-cow

chalk-integration/src/lowering.rs

@@ -1827,6 +1827,7 @@ impl LowerWellKnownTrait for WellKnownTrait {
             Self::FnOnce => rust_ir::WellKnownTrait::FnOnce,
             Self::FnMut => rust_ir::WellKnownTrait::FnMut,
             Self::Fn => rust_ir::WellKnownTrait::Fn,
+            Self::Unsize => rust_ir::WellKnownTrait::Unsize,
         }
     }
 }

chalk-ir/src/debug.rs

@@ -210,7 +210,6 @@ impl<I: Interner> Debug for DynTy<I> {
         write!(fmt, "dyn {:?} + {:?}", bounds, lifetime)
     }
 }
-
 impl Debug for InferenceVar {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> Result<(), Error> {
         write!(fmt, "?{}", self.index)

chalk-ir/src/lib.rs

@@ -1351,6 +1351,15 @@ impl<I: Interner> WhereClause<I> {
             wc => wc.cast(interner),
         }
     }
+
+    /// If where clause is a `TraitRef`, returns its trait id
+    pub fn trait_id(&self) -> Option<TraitId<I>> {
+        match self {
+            WhereClause::Implemented(trait_ref) => Some(trait_ref.trait_id),
+            WhereClause::AliasEq(_) => None,
+            WhereClause::LifetimeOutlives(_) => None,
+        }
+    }
 }
 
 impl<I: Interner> QuantifiedWhereClause<I> {
@@ -1369,6 +1378,11 @@ impl<I: Interner> QuantifiedWhereClause<I> {
     pub fn into_from_env_goal(self, interner: &I) -> Binders<DomainGoal<I>> {
         self.map(|wc| wc.into_from_env_goal(interner))
     }
+
+    /// If the underlying where clause is a `TraitRef`, returns its trait id
+    pub fn trait_id(&self) -> Option<TraitId<I>> {
+        self.skip_binders().trait_id()
+    }
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, HasInterner)]

chalk-parse/src/ast.rs

@@ -71,6 +71,7 @@ pub enum WellKnownTrait {
     FnOnce,
     FnMut,
     Fn,
+    Unsize,
 }
 
 #[derive(Clone, PartialEq, Eq, Debug)]

chalk-parse/src/parser.lalrpop

@@ -54,6 +54,7 @@ WellKnownTrait: WellKnownTrait = {
      "#" "[" "lang" "(" "fn_once" ")" "]" => WellKnownTrait::FnOnce,
      "#" "[" "lang" "(" "fn_mut" ")" "]" => WellKnownTrait::FnMut,
      "#" "[" "lang" "(" "fn" ")" "]" => WellKnownTrait::Fn,
+     "#" "[" "lang" "(" "unsize" ")" "]" => WellKnownTrait::Unsize,
 };
 
 StructDefn: StructDefn = {

chalk-solve/src/clauses/builtin_traits.rs

@@ -6,6 +6,7 @@ mod clone;
 mod copy;
 mod fn_family;
 mod sized;
+mod unsize;
 
 /// For well known traits we have special hard-coded impls, either as an
 /// optimization or to enforce special rules for correctness.
@@ -36,6 +37,9 @@ pub fn add_builtin_program_clauses<I: Interner>(
             WellKnownTrait::FnOnce | WellKnownTrait::FnMut | WellKnownTrait::Fn => {
                 fn_family::add_fn_trait_program_clauses(db, builder, trait_ref.trait_id, self_ty)?
             }
+            WellKnownTrait::Unsize => {
+                unsize::add_unsize_program_clauses(db, builder, &trait_ref, ty)
+            }
             // Drop impls are provided explicitly
             WellKnownTrait::Drop => (),
         }