1 files changed, 73 insertions, 53 deletions

diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 6b7918187..667b66095 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -129,85 +129,105 @@ impl Ty {
         name: &Name,
         resolver: &Resolver,
     ) -> Option<(Ty, Function)> {
-        // FIXME: trait methods should be used before autoderefs
-        // (and we need to do autoderefs for trait method calls as well)
-        let inherent_method = self.clone().iterate_methods(db, |ty, f| {
-            let sig = f.signature(db);
-            if sig.name() == name && sig.has_self_param() {
-                Some((ty.clone(), f))
-            } else {
-                None
-            }
-        });
-        inherent_method.or_else(|| self.lookup_trait_method(db, name, resolver))
+        self.iterate_method_candidates(db, resolver, Some(name), |ty, f| Some((ty.clone(), f)))
     }
 
-    fn lookup_trait_method(
+    // This would be nicer if it just returned an iterator, but that runs into
+    // lifetime problems, because we need to borrow temp `CrateImplBlocks`.
+    pub(crate) fn iterate_method_candidates<T>(
         self,
         db: &impl HirDatabase,
-        name: &Name,
         resolver: &Resolver,
-    ) -> Option<(Ty, Function)> {
-        let mut candidates = Vec::new();
-        for t in resolver.traits_in_scope() {
+        name: Option<&Name>,
+        mut callback: impl FnMut(&Ty, Function) -> Option<T>,
+    ) -> Option<T> {
+        // For method calls, rust first does any number of autoderef, and then one
+        // autoref (i.e. when the method takes &self or &mut self). We just ignore
+        // the autoref currently -- when we find a method matching the given name,
+        // we assume it fits.
+
+        // Also note that when we've got a receiver like &S, even if the method we
+        // find in the end takes &self, we still do the autoderef step (just as
+        // rustc does an autoderef and then autoref again).
+
+        for derefed_ty in self.autoderef(db) {
+            if let Some(result) = derefed_ty.iterate_inherent_methods(db, name, &mut callback) {
+                return Some(result);
+            }
+            if let Some(result) =
+                derefed_ty.iterate_trait_method_candidates(db, resolver, name, &mut callback)
+            {
+                return Some(result);
+            }
+        }
+        None
+    }
+
+    fn iterate_trait_method_candidates<T>(
+        &self,
+        db: &impl HirDatabase,
+        resolver: &Resolver,
+        name: Option<&Name>,
+        mut callback: impl FnMut(&Ty, Function) -> Option<T>,
+    ) -> Option<T> {
+        'traits: for t in resolver.traits_in_scope() {
             let data = t.trait_data(db);
+            // we'll be lazy about checking whether the type implements the
+            // trait, but if we find out it doesn't, we'll skip the rest of the
+            // iteration
+            let mut known_implemented = false;
             for item in data.items() {
                 match item {
                     &TraitItem::Function(m) => {
                         let sig = m.signature(db);
-                        if sig.name() == name && sig.has_self_param() {
-                            candidates.push((t, m));
+                        if name.map_or(true, |name| sig.name() == name) && sig.has_self_param() {
+                            if !known_implemented {
+                                let trait_ref = TraitRef {
+                                    trait_: t,
+                                    substs: fresh_substs_for_trait(db, t, self.clone()),
+                                };
+                                let (trait_ref, _) = super::traits::canonicalize(trait_ref);
+                                if db.implements(trait_ref).is_none() {
+                                    continue 'traits;
+                                }
+                            }
+                            known_implemented = true;
+                            if let Some(result) = callback(self, m) {
+                                return Some(result);
+                            }
                         }
                     }
                     _ => {}
                 }
             }
         }
-        candidates.retain(|(t, _m)| {
-            let trait_ref =
-                TraitRef { trait_: *t, substs: fresh_substs_for_trait(db, *t, self.clone()) };
-            let (trait_ref, _) = super::traits::canonicalize(trait_ref);
-            db.implements(trait_ref).is_some()
-        });
-        // FIXME if there's multiple candidates here, that's an ambiguity error
-        let (_chosen_trait, chosen_method) = candidates.first()?;
-        // FIXME return correct receiver type
-        Some((self.clone(), *chosen_method))
+        None
     }
 
-    // This would be nicer if it just returned an iterator, but that runs into
-    // lifetime problems, because we need to borrow temp `CrateImplBlocks`.
-    pub fn iterate_methods<T>(
-        self,
+    fn iterate_inherent_methods<T>(
+        &self,
         db: &impl HirDatabase,
+        name: Option<&Name>,
         mut callback: impl FnMut(&Ty, Function) -> Option<T>,
     ) -> Option<T> {
-        // For method calls, rust first does any number of autoderef, and then one
-        // autoref (i.e. when the method takes &self or &mut self). We just ignore
-        // the autoref currently -- when we find a method matching the given name,
-        // we assume it fits.
-
-        // Also note that when we've got a receiver like &S, even if the method we
-        // find in the end takes &self, we still do the autoderef step (just as
-        // rustc does an autoderef and then autoref again).
+        let krate = match def_crate(db, self) {
+            Some(krate) => krate,
+            None => return None,
+        };
+        let impls = db.impls_in_crate(krate);
 
-        for derefed_ty in self.autoderef(db) {
-            let krate = match def_crate(db, &derefed_ty) {
-                Some(krate) => krate,
-                None => continue,
-            };
-            let impls = db.impls_in_crate(krate);
-
-            for impl_block in impls.lookup_impl_blocks(&derefed_ty) {
-                for item in impl_block.items(db) {
-                    match item {
-                        ImplItem::Method(f) => {
-                            if let Some(result) = callback(&derefed_ty, f) {
+        for impl_block in impls.lookup_impl_blocks(self) {
+            for item in impl_block.items(db) {
+                match item {
+                    ImplItem::Method(f) => {
+                        let sig = f.signature(db);
+                        if name.map_or(true, |name| sig.name() == name) && sig.has_self_param() {
+                            if let Some(result) = callback(self, f) {
                                 return Some(result);
                             }
                         }
-                        _ => {}
                     }
+                    _ => {}
                 }
             }
         }