Parse #[deref], add rudimentary lang item infrastructure.

Author: leoyvens

chalk-parse/src/ast.rs

@@ -48,6 +48,7 @@ pub struct TraitFlags {
     pub auto: bool,
     pub marker: bool,
     pub external: bool,
+    pub deref: bool,
 }
 
 pub struct AssocTyDefn {

chalk-parse/src/parser.lalrpop

@@ -38,6 +38,7 @@ Goal1: Box<Goal> = {
 ExternalKeyword: () = "extern";
 AutoKeyword: () = "#" "[" "auto" "]";
 MarkerKeyword: () = "#" "[" "marker" "]";
+DerefKeyword: () = "#" "[" "deref" "]";
 
 StructDefn: StructDefn = {
     <external:ExternalKeyword?> "struct" <n:Id><p:Angle<ParameterKind>>
@@ -54,7 +55,7 @@ StructDefn: StructDefn = {
 };
 
 TraitDefn: TraitDefn = {
-    <external:ExternalKeyword?> <auto:AutoKeyword?> <marker:MarkerKeyword?> "trait" <n:Id><p:Angle<ParameterKind>>
+    <external:ExternalKeyword?> <auto:AutoKeyword?> <marker:MarkerKeyword?> <deref:DerefKeyword?> "trait" <n:Id><p:Angle<ParameterKind>>
         <w:QuantifiedWhereClauses> "{" <a:AssocTyDefn*> "}" => TraitDefn
     {
         name: n,
@@ -65,6 +66,7 @@ TraitDefn: TraitDefn = {
             auto: auto.is_some(),
             marker: marker.is_some(),
             external: external.is_some(),
+            deref: deref.is_some(),
         },
     }
 };

src/errors.rs

@@ -50,5 +50,10 @@ error_chain! {
             description("could not match")
                 display("could not match")
         }
+
+        DuplicateLangItem(item: ir::LangItem) {
+            description("Duplicate lang item")
+                display("Duplicate lang item `{:?}`", item)
+        }
     }
 }

src/ir/mod.rs

@@ -38,6 +38,9 @@ pub struct Program {
 
     /// For each user-specified clause
     crate custom_clauses: Vec<ProgramClause>,
+
+    /// Special types and traits.
+    crate lang_items: BTreeMap<LangItem, ItemId>,
 }
 
 impl Program {
@@ -71,6 +74,11 @@ pub struct ProgramEnvironment {
     crate program_clauses: Vec<ProgramClause>,
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum LangItem {
+    DerefTrait,
+}
+
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
 /// The set of assumptions we've made so far, and the current number of
 /// universal (forall) quantifiers we're within.
@@ -244,6 +252,7 @@ pub struct TraitFlags {
     crate auto: bool,
     crate marker: bool,
     crate external: bool,
+    pub deref: bool,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]

src/lower/mod.rs

@@ -172,6 +172,7 @@ impl LowerProgram for Program {
         let mut impl_data = BTreeMap::new();
         let mut associated_ty_data = BTreeMap::new();
         let mut custom_clauses = Vec::new();
+        let mut lang_items = BTreeMap::new();
         for (item, &item_id) in self.items.iter().zip(&item_ids) {
             let empty_env = Env {
                 type_ids: &type_ids,
@@ -204,6 +205,16 @@ impl LowerProgram for Program {
                             },
                         );
                     }
+
+                    if d.flags.deref {
+                        use std::collections::btree_map::Entry::*;
+                        match lang_items.entry(ir::LangItem::DerefTrait) {
+                            Vacant(entry) => { entry.insert(item_id); },
+                            Occupied(_) => {
+                                bail!(ErrorKind::DuplicateLangItem(ir::LangItem::DerefTrait))
+                            }
+                        }
+                    }
                 }
                 Item::Impl(ref d) => {
                     impl_data.insert(item_id, d.lower_impl(&empty_env)?);
@@ -222,6 +233,7 @@ impl LowerProgram for Program {
             impl_data,
             associated_ty_data,
             custom_clauses,
+            lang_items,
             default_impl_data: Vec::new(),
         };
         program.add_default_impls();
@@ -903,6 +915,7 @@ impl LowerTrait for TraitDefn {
                     auto: self.flags.auto,
                     marker: self.flags.marker,
                     external: self.flags.external,
+                    deref: self.flags.deref,
                 },
             })
         })?;

src/lower/test.rs

@@ -850,3 +850,21 @@ fn higher_ranked_cyclic_requirements() {
         }
     }
 }
+
+#[test]
+fn deref_trait() {
+    lowering_success! {
+        program {
+            #[deref] trait Deref { type Target; }
+        }
+    }
+
+    lowering_error! {
+        program {
+            #[deref] trait Deref { }
+            #[deref] trait DerefDupe { }
+        } error_msg {
+            "Duplicate lang item `DerefTrait`"
+        }
+    }
+}