5 files changed, 33 insertions, 10 deletions

diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 8aaf0375a..689dd6225 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -161,6 +161,13 @@ pub trait HirDatabase: DefDatabase {
     #[salsa::invoke(crate::ty::traits::solver)]
     #[salsa::volatile]
     fn solver(&self, krate: Crate) -> Arc<Mutex<crate::ty::traits::Solver>>;
+
+    #[salsa::invoke(crate::ty::traits::implements)]
+    fn implements(
+        &self,
+        krate: Crate,
+        goal: crate::ty::Canonical<crate::ty::TraitRef>,
+    ) -> Option<crate::ty::traits::Solution>;
 }
 
 #[test]
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index f4eee835f..12429a668 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -240,7 +240,7 @@ impl TraitRef {
 /// many there are. This is used to erase irrelevant differences between types
 /// before using them in queries.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub(crate) struct Canonical<T> {
+pub struct Canonical<T> {
     pub value: T,
     pub num_vars: usize,
 }
@@ -534,3 +534,20 @@ impl HirDisplay for Ty {
         Ok(())
     }
 }
+
+impl HirDisplay for TraitRef {
+    fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result {
+        write!(
+            f,
+            "{}: {}",
+            self.substs[0].display(f.db),
+            self.trait_.name(f.db).unwrap_or_else(Name::missing)
+        )?;
+        if self.substs.len() > 1 {
+            write!(f, "<")?;
+            f.write_joined(&self.substs[1..], ", ")?;
+            write!(f, ">")?;
+        }
+        Ok(())
+    }
+}
diff --git a/crates/ra_hir/src/ty/infer.rs b/crates/ra_hir/src/ty/infer.rs
index edce1afe7..1e7d97f51 100644
--- a/crates/ra_hir/src/ty/infer.rs
+++ b/crates/ra_hir/src/ty/infer.rs
@@ -328,8 +328,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 Obligation::Trait(tr) => {
                     let canonicalized = self.canonicalizer().canonicalize_trait_ref(tr.clone());
                     (
-                        super::traits::implements(
-                            self.db,
+                        self.db.implements(
                             self.resolver.krate().unwrap(),
                             canonicalized.value.clone(),
                         ),
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index 607e9ba79..d8b8c836c 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -196,8 +196,7 @@ fn iterate_trait_method_candidates<T>(
                     if name.map_or(true, |name| sig.name() == name) && sig.has_self_param() {
                         if !known_implemented {
                             let trait_ref = canonical_trait_ref(db, t, ty.clone());
-                            // FIXME cache this implements check (without solution) in a query?
-                            if super::traits::implements(db, krate, trait_ref).is_none() {
+                            if db.implements(krate, trait_ref).is_none() {
                                 continue 'traits;
                             }
                         }
diff --git a/crates/ra_hir/src/ty/traits.rs b/crates/ra_hir/src/ty/traits.rs
index a1ed0c028..4bbc99f0e 100644
--- a/crates/ra_hir/src/ty/traits.rs
+++ b/crates/ra_hir/src/ty/traits.rs
@@ -1,6 +1,7 @@
 //! Trait solving using Chalk.
 use std::sync::{Arc, Mutex};
 
+use rustc_hash::FxHashSet;
 use log::debug;
 use chalk_ir::cast::Cast;
 
@@ -31,7 +32,7 @@ pub(crate) fn impls_for_trait(
     krate: Crate,
     trait_: Trait,
 ) -> Arc<[ImplBlock]> {
-    let mut impls = Vec::new();
+    let mut impls = FxHashSet::default();
     // We call the query recursively here. On the one hand, this means we can
     // reuse results from queries for different crates; on the other hand, this
     // will only ever get called for a few crates near the root of the tree (the
@@ -42,7 +43,7 @@ pub(crate) fn impls_for_trait(
     }
     let crate_impl_blocks = db.impls_in_crate(krate);
     impls.extend(crate_impl_blocks.lookup_impl_blocks_for_trait(&trait_));
-    impls.into()
+    impls.into_iter().collect::<Vec<_>>().into()
 }
 
 fn solve(
@@ -125,11 +126,11 @@ fn solution_from_chalk(db: &impl HirDatabase, solution: chalk_solve::Solution) -
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub(crate) struct SolutionVariables(pub Canonical<Vec<Ty>>);
+pub struct SolutionVariables(pub Canonical<Vec<Ty>>);
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 /// A (possible) solution for a proposed goal.
-pub(crate) enum Solution {
+pub enum Solution {
     /// The goal indeed holds, and there is a unique value for all existential
     /// variables.
     Unique(SolutionVariables),
@@ -144,7 +145,7 @@ pub(crate) enum Solution {
 #[derive(Clone, Debug, PartialEq, Eq)]
 /// When a goal holds ambiguously (e.g., because there are multiple possible
 /// solutions), we issue a set of *guidance* back to type inference.
-pub(crate) enum Guidance {
+pub enum Guidance {
     /// The existential variables *must* have the given values if the goal is
     /// ever to hold, but that alone isn't enough to guarantee the goal will
     /// actually hold.