Detangle ty from traits a bit

3 files changed, 55 insertions, 3 deletions

diff --git a/crates/ra_hir/src/ty/lower.rs b/crates/ra_hir/src/ty/lower.rs
index 2d23890a5..9e3afabe0 100644
--- a/crates/ra_hir/src/ty/lower.rs
+++ b/crates/ra_hir/src/ty/lower.rs
@@ -28,6 +28,7 @@ use crate::{
     db::HirDatabase,
     ty::{
         primitive::{FloatTy, IntTy},
+        utils::all_super_traits,
         Adt,
     },
     util::make_mut_slice,
@@ -260,7 +261,7 @@ impl Ty {
             GenericPredicate::Implemented(tr) if tr.self_ty() == &self_ty => Some(tr.trait_),
             _ => None,
         });
-        let traits = traits_from_env.flat_map(|t| t.all_super_traits(db));
+        let traits = traits_from_env.flat_map(|t| all_super_traits(db, t.id)).map(Trait::from);
         for t in traits {
             if let Some(associated_ty) = t.associated_type_by_name(db, &segment.name) {
                 let substs = Substs::build_for_def(db, t.id)
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 489fcd64b..0e18684ed 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -16,7 +16,7 @@ use rustc_hash::FxHashMap;
 use crate::{
     db::HirDatabase,
     ty::primitive::{FloatBitness, Uncertain},
-    ty::{Ty, TypeCtor},
+    ty::{utils::all_super_traits, Ty, TypeCtor},
     AssocItem, Crate, Function, Mutability, Name, Trait,
 };
 
@@ -249,7 +249,8 @@ fn iterate_trait_method_candidates<T>(
     let traits_from_env = env
         .trait_predicates_for_self_ty(&ty.value)
         .map(|tr| tr.trait_)
-        .flat_map(|t| t.all_super_traits(db));
+        .flat_map(|t| all_super_traits(db, t.id))
+        .map(Trait::from);
     let traits = inherent_trait
         .chain(traits_from_env)
         .chain(resolver.traits_in_scope(db).into_iter().map(Trait::from));
diff --git a/crates/ra_hir/src/ty/utils.rs b/crates/ra_hir/src/ty/utils.rs
new file mode 100644
index 000000000..345fa9430
--- /dev/null
+++ b/crates/ra_hir/src/ty/utils.rs
@@ -0,0 +1,50 @@
+use hir_def::{
+    db::DefDatabase,
+    resolver::{HasResolver, TypeNs},
+    type_ref::TypeRef,
+    TraitId,
+};
+use hir_expand::name;
+
+// FIXME: this is wrong, b/c it can't express `trait T: PartialEq<()>`.
+// We should return a `TraitREf` here.
+fn direct_super_traits(db: &impl DefDatabase, trait_: TraitId) -> Vec<TraitId> {
+    let resolver = trait_.resolver(db);
+    // returning the iterator directly doesn't easily work because of
+    // lifetime problems, but since there usually shouldn't be more than a
+    // few direct traits this should be fine (we could even use some kind of
+    // SmallVec if performance is a concern)
+    db.generic_params(trait_.into())
+        .where_predicates
+        .iter()
+        .filter_map(|pred| match &pred.type_ref {
+            TypeRef::Path(p) if p.as_ident() == Some(&name::SELF_TYPE) => pred.bound.as_path(),
+            _ => None,
+        })
+        .filter_map(|path| match resolver.resolve_path_in_type_ns_fully(db, path) {
+            Some(TypeNs::TraitId(t)) => Some(t),
+            _ => None,
+        })
+        .collect()
+}
+
+/// Returns an iterator over the whole super trait hierarchy (including the
+/// trait itself).
+pub(crate) fn all_super_traits(db: &impl DefDatabase, trait_: TraitId) -> Vec<TraitId> {
+    // we need to take care a bit here to avoid infinite loops in case of cycles
+    // (i.e. if we have `trait A: B; trait B: A;`)
+    let mut result = vec![trait_];
+    let mut i = 0;
+    while i < result.len() {
+        let t = result[i];
+        // yeah this is quadratic, but trait hierarchies should be flat
+        // enough that this doesn't matter
+        for tt in direct_super_traits(db, t) {
+            if !result.contains(&tt) {
+                result.push(tt);
+            }
+        }
+        i += 1;
+    }
+    result
+}