Handle where clauses in trait solving

3 files changed, 138 insertions, 24 deletions

diff --git a/crates/ra_hir/src/ty/lower.rs b/crates/ra_hir/src/ty/lower.rs
index 8bab7e54b..09d26ce5a 100644
--- a/crates/ra_hir/src/ty/lower.rs
+++ b/crates/ra_hir/src/ty/lower.rs
@@ -5,6 +5,7 @@
 //!  - Building the type for an item: This happens through the `type_for_def` query.
 //!
 //! This usually involves resolving names, collecting generic arguments etc.
+use std::sync::Arc;
 use std::iter;
 
 use crate::{
@@ -18,9 +19,9 @@ use crate::{
     resolve::{Resolver, Resolution},
     path::{PathSegment, GenericArg},
     generics::{GenericParams, HasGenericParams},
-    adt::VariantDef, Trait
+    adt::VariantDef, Trait, generics::{ WherePredicate, GenericDef}
 };
-use super::{Ty, primitive, FnSig, Substs, TypeCtor, TraitRef};
+use super::{Ty, primitive, FnSig, Substs, TypeCtor, TraitRef, GenericPredicate};
 
 impl Ty {
     pub(crate) fn from_hir(db: &impl HirDatabase, resolver: &Resolver, type_ref: &TypeRef) -> Self {
@@ -208,16 +209,12 @@ pub(super) fn substs_from_path_segment(
 }
 
 impl TraitRef {
-    pub(crate) fn from_hir(
+    pub(crate) fn from_path(
         db: &impl HirDatabase,
         resolver: &Resolver,
-        type_ref: &TypeRef,
+        path: &Path,
         explicit_self_ty: Option<Ty>,
     ) -> Option<Self> {
-        let path = match type_ref {
-            TypeRef::Path(path) => path,
-            _ => return None,
-        };
         let resolved = match resolver.resolve_path(db, &path).take_types()? {
             Resolution::Def(ModuleDef::Trait(tr)) => tr,
             _ => return None,
@@ -232,6 +229,19 @@ impl TraitRef {
         Some(TraitRef { trait_: resolved, substs })
     }
 
+    pub(crate) fn from_hir(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        type_ref: &TypeRef,
+        explicit_self_ty: Option<Ty>,
+    ) -> Option<Self> {
+        let path = match type_ref {
+            TypeRef::Path(path) => path,
+            _ => return None,
+        };
+        TraitRef::from_path(db, resolver, path, explicit_self_ty)
+    }
+
     fn substs_from_path(
         db: &impl HirDatabase,
         resolver: &Resolver,
@@ -246,6 +256,15 @@ impl TraitRef {
         let substs = Substs::identity(&trait_.generic_params(db));
         TraitRef { trait_, substs }
     }
+
+    pub(crate) fn for_where_predicate(
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        pred: &WherePredicate,
+    ) -> Option<TraitRef> {
+        let self_ty = Ty::from_hir(db, resolver, &pred.type_ref);
+        TraitRef::from_path(db, resolver, &pred.trait_ref, Some(self_ty))
+    }
 }
 
 /// Build the declared type of an item. This depends on the namespace; e.g. for
@@ -294,6 +313,24 @@ pub(crate) fn type_for_field(db: &impl HirDatabase, field: StructField) -> Ty {
     Ty::from_hir(db, &resolver, type_ref)
 }
 
+/// Resolve the where clause(s) of an item with generics.
+pub(crate) fn generic_predicates(
+    db: &impl HirDatabase,
+    def: GenericDef,
+) -> Arc<[GenericPredicate]> {
+    let resolver = def.resolver(db);
+    let generic_params = def.generic_params(db);
+    let predicates = generic_params
+        .where_predicates
+        .iter()
+        .map(|pred| {
+            TraitRef::for_where_predicate(db, &resolver, pred)
+                .map_or(GenericPredicate::Error, GenericPredicate::Implemented)
+        })
+        .collect::<Vec<_>>();
+    predicates.into()
+}
+
 fn fn_sig_for_fn(db: &impl HirDatabase, def: Function) -> FnSig {
     let signature = def.signature(db);
     let resolver = def.resolver(db);
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index a38fe35c7..c3edf42b1 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -2510,12 +2510,47 @@ fn method_resolution_where_clause_not_met() {
 trait Clone {}
 trait Trait { fn foo(self) -> u128; }
 struct S;
-impl S { fn foo(self) -> i8 { 0 } }
-impl<T> Trait for T where T: Clone { fn foo(self) -> u128 { 0 } }
+impl<T> Trait for T where T: Clone {}
 fn test() { (&S).foo()<|>; }
 "#,
     );
-    assert_eq!(t, "i8");
+    // This is also to make sure that we don't resolve to the foo method just
+    // because that's the only method named foo we can find, which would make
+    // the below tests not work
+    assert_eq!(t, "{unknown}");
+}
+
+#[test]
+fn method_resolution_where_clause_1() {
+    let t = type_at(
+        r#"
+//- /main.rs
+trait Clone {}
+trait Trait { fn foo(self) -> u128; }
+struct S;
+impl Clone for S {};
+impl<T> Trait for T where T: Clone {}
+fn test() { S.foo()<|>; }
+"#,
+    );
+    assert_eq!(t, "u128");
+}
+
+#[test]
+fn method_resolution_where_clause_2() {
+    let t = type_at(
+        r#"
+//- /main.rs
+trait Into<T> { fn into(self) -> T; }
+trait From<T> { fn from(other: T) -> Self; }
+struct S1;
+struct S2;
+impl From<S2> for S1 {};
+impl<T, U> Into<U> for T where U: From<T> {}
+fn test() { S2.into()<|>; }
+"#,
+    );
+    assert_eq!(t, "S1");
 }
 
 fn type_at_pos(db: &MockDatabase, pos: FilePosition) -> String {
diff --git a/crates/ra_hir/src/ty/traits/chalk.rs b/crates/ra_hir/src/ty/traits/chalk.rs
index 8b77d21b4..2772a0432 100644
--- a/crates/ra_hir/src/ty/traits/chalk.rs
+++ b/crates/ra_hir/src/ty/traits/chalk.rs
@@ -11,7 +11,7 @@ use ra_db::salsa::{InternId, InternKey};
 use crate::{
     Trait, HasGenericParams, ImplBlock,
     db::HirDatabase,
-    ty::{TraitRef, Ty, ApplicationTy, TypeCtor, Substs},
+    ty::{TraitRef, Ty, ApplicationTy, TypeCtor, Substs, GenericPredicate}, generics::GenericDef,
 };
 use super::ChalkContext;
 
@@ -146,6 +146,27 @@ impl ToChalk for ImplBlock {
     }
 }
 
+impl ToChalk for GenericPredicate {
+    type Chalk = chalk_ir::QuantifiedWhereClause;
+
+    fn to_chalk(self, db: &impl HirDatabase) -> chalk_ir::QuantifiedWhereClause {
+        match self {
+            GenericPredicate::Implemented(trait_ref) => {
+                make_binders(chalk_ir::WhereClause::Implemented(trait_ref.to_chalk(db)), 0)
+            }
+            GenericPredicate::Error => panic!("Trying to pass errored where clause to Chalk"),
+        }
+    }
+
+    fn from_chalk(
+        _db: &impl HirDatabase,
+        _where_clause: chalk_ir::QuantifiedWhereClause,
+    ) -> GenericPredicate {
+        // This should never need to be called
+        unimplemented!()
+    }
+}
+
 fn make_binders<T>(value: T, num_vars: usize) -> chalk_ir::Binders<T> {
     chalk_ir::Binders {
         value,
@@ -153,6 +174,25 @@ fn make_binders<T>(value: T, num_vars: usize) -> chalk_ir::Binders<T> {
     }
 }
 
+fn convert_where_clauses(
+    db: &impl HirDatabase,
+    def: GenericDef,
+    substs: &Substs,
+) -> (Vec<chalk_ir::QuantifiedWhereClause>, bool) {
+    let generic_predicates = db.generic_predicates(def);
+    let mut result = Vec::with_capacity(generic_predicates.len());
+    let mut has_error = false;
+    for pred in generic_predicates.iter() {
+        // FIXME: it would probably be nicer if we could just convert errored predicates to a where clause that is never true...
+        if pred.is_error() {
+            has_error = true;
+        } else {
+            result.push(pred.clone().subst(substs).to_chalk(db));
+        }
+    }
+    (result, has_error)
+}
+
 impl<'a, DB> chalk_solve::RustIrDatabase for ChalkContext<'a, DB>
 where
     DB: HirDatabase,
@@ -173,7 +213,7 @@ where
             upstream: trait_.module(self.db).krate(self.db) != Some(self.krate),
             fundamental: false,
         };
-        let where_clauses = Vec::new(); // FIXME add where clauses
+        let (where_clauses, _) = convert_where_clauses(self.db, trait_.into(), &bound_vars);
         let associated_ty_ids = Vec::new(); // FIXME add associated tys
         let trait_datum_bound =
             chalk_rust_ir::TraitDatumBound { trait_ref, where_clauses, flags, associated_ty_ids };
@@ -185,21 +225,26 @@ where
         let type_ctor = from_chalk(self.db, struct_id);
         // FIXME might be nicer if we can create a fake GenericParams for the TypeCtor
         // FIXME extract this to a method on Ty
-        let (num_params, upstream) = match type_ctor {
+        let (num_params, where_clauses, upstream) = match type_ctor {
             TypeCtor::Bool
             | TypeCtor::Char
             | TypeCtor::Int(_)
             | TypeCtor::Float(_)
             | TypeCtor::Never
-            | TypeCtor::Str => (0, true),
-            TypeCtor::Slice | TypeCtor::Array | TypeCtor::RawPtr(_) | TypeCtor::Ref(_) => (1, true),
-            TypeCtor::FnPtr { num_args } => (num_args as usize + 1, true),
-            TypeCtor::Tuple { cardinality } => (cardinality as usize, true),
+            | TypeCtor::Str => (0, vec![], true),
+            TypeCtor::Slice | TypeCtor::Array | TypeCtor::RawPtr(_) | TypeCtor::Ref(_) => {
+                (1, vec![], true)
+            }
+            TypeCtor::FnPtr { num_args } => (num_args as usize + 1, vec![], true),
+            TypeCtor::Tuple { cardinality } => (cardinality as usize, vec![], true),
             TypeCtor::FnDef(_) => unimplemented!(),
             TypeCtor::Adt(adt) => {
                 let generic_params = adt.generic_params(self.db);
+                let bound_vars = Substs::bound_vars(&generic_params);
+                let (where_clauses, _) = convert_where_clauses(self.db, adt.into(), &bound_vars);
                 (
                     generic_params.count_params_including_parent(),
+                    where_clauses,
                     adt.krate(self.db) != Some(self.krate),
                 )
             }
@@ -209,7 +254,6 @@ where
             // FIXME set fundamental flag correctly
             fundamental: false,
         };
-        let where_clauses = Vec::new(); // FIXME add where clauses
         let self_ty = chalk_ir::ApplicationTy {
             name: TypeName::TypeKindId(type_ctor.to_chalk(self.db).into()),
             parameters: (0..num_params).map(|i| chalk_ir::Ty::BoundVar(i).cast()).collect(),
@@ -237,10 +281,12 @@ where
         } else {
             chalk_rust_ir::ImplType::External
         };
+        let (where_clauses, where_clause_error) =
+            convert_where_clauses(self.db, impl_block.into(), &bound_vars);
         let impl_datum_bound = chalk_rust_ir::ImplDatumBound {
             // FIXME handle negative impls (impl !Sync for Foo)
             trait_ref: chalk_rust_ir::PolarizedTraitRef::Positive(trait_ref.to_chalk(self.db)),
-            where_clauses: Vec::new(),        // FIXME add where clauses
+            where_clauses,
             associated_ty_values: Vec::new(), // FIXME add associated type values
             impl_type,
         };
@@ -253,10 +299,6 @@ where
         self.db
             .impls_for_trait(self.krate, trait_)
             .iter()
-            // FIXME temporary hack -- as long as we're not lowering where clauses
-            // correctly, ignore impls with them completely so as to not treat
-            // impl<T> Trait for T where T: ... as a blanket impl on all types
-            .filter(|impl_block| impl_block.generic_params(self.db).where_predicates.is_empty())
             .map(|impl_block| impl_block.to_chalk(self.db))
             .collect()
     }