3 files changed, 314 insertions, 82 deletions

diff --git a/crates/ra_hir/src/ty/infer/path.rs b/crates/ra_hir/src/ty/infer/path.rs
index 77aa35ce1..59b7f7eb6 100644
--- a/crates/ra_hir/src/ty/infer/path.rs
+++ b/crates/ra_hir/src/ty/infer/path.rs
@@ -6,8 +6,8 @@ use super::{ExprOrPatId, InferenceContext, TraitRef};
 use crate::{
     db::HirDatabase,
     resolve::{ResolveValueResult, Resolver, TypeNs, ValueNs},
-    ty::{Substs, Ty, TypableDef, TypeWalk},
-    AssocItem, HasGenericParams, Namespace, Path,
+    ty::{method_resolution, Substs, Ty, TypableDef, TypeWalk},
+    AssocItem, Container, HasGenericParams, Name, Namespace, Path,
 };
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
@@ -39,7 +39,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             let ty = Ty::from_type_relative_path(self.db, resolver, ty, remaining_segments_for_ty);
             self.resolve_ty_assoc_item(
                 ty,
-                path.segments.last().expect("path had at least one segment"),
+                &path.segments.last().expect("path had at least one segment").name,
                 id,
             )?
         } else {
@@ -122,10 +122,13 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     return None;
                 }
 
+                let ty = self.insert_type_vars(ty);
+                let ty = self.normalize_associated_types_in(ty);
+
                 let segment =
                     remaining_segments.last().expect("there should be at least one segment here");
 
-                self.resolve_ty_assoc_item(ty, segment, id)
+                self.resolve_ty_assoc_item(ty, &segment.name, id)
             }
         }
     }
@@ -162,7 +165,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         };
         let substs = Substs::build_for_def(self.db, item)
             .use_parent_substs(&trait_ref.substs)
-            .fill_with_unknown()
+            .fill_with_params()
             .build();
 
         self.write_assoc_resolution(id, item);
@@ -172,44 +175,51 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn resolve_ty_assoc_item(
         &mut self,
         ty: Ty,
-        segment: &PathSegment,
+        name: &Name,
         id: ExprOrPatId,
     ) -> Option<(ValueNs, Option<Substs>)> {
         if let Ty::Unknown = ty {
             return None;
         }
 
-        let krate = self.resolver.krate()?;
-
-        // Find impl
-        // FIXME: consider trait candidates
-        let item = ty.clone().iterate_impl_items(self.db, krate, |item| match item {
-            AssocItem::Function(func) => {
-                if segment.name == func.name(self.db) {
-                    Some(AssocItem::Function(func))
-                } else {
-                    None
-                }
-            }
-
-            AssocItem::Const(konst) => {
-                if konst.name(self.db).map_or(false, |n| n == segment.name) {
-                    Some(AssocItem::Const(konst))
-                } else {
-                    None
-                }
-            }
-            AssocItem::TypeAlias(_) => None,
-        })?;
-        let def = match item {
-            AssocItem::Function(f) => ValueNs::Function(f),
-            AssocItem::Const(c) => ValueNs::Const(c),
-            AssocItem::TypeAlias(_) => unreachable!(),
-        };
-        let substs = self.find_self_types(&def, ty);
+        let canonical_ty = self.canonicalizer().canonicalize_ty(ty.clone());
+
+        method_resolution::iterate_method_candidates(
+            &canonical_ty.value,
+            self.db,
+            &self.resolver.clone(),
+            Some(name),
+            method_resolution::LookupMode::Path,
+            move |_ty, item| {
+                let def = match item {
+                    AssocItem::Function(f) => ValueNs::Function(f),
+                    AssocItem::Const(c) => ValueNs::Const(c),
+                    AssocItem::TypeAlias(_) => unreachable!(),
+                };
+                let substs = match item.container(self.db) {
+                    Container::ImplBlock(_) => self.find_self_types(&def, ty.clone()),
+                    Container::Trait(t) => {
+                        // we're picking this method
+                        let trait_substs = Substs::build_for_def(self.db, t)
+                            .push(ty.clone())
+                            .fill(std::iter::repeat_with(|| self.new_type_var()))
+                            .build();
+                        let substs = Substs::build_for_def(self.db, item)
+                            .use_parent_substs(&trait_substs)
+                            .fill_with_params()
+                            .build();
+                        self.obligations.push(super::Obligation::Trait(TraitRef {
+                            trait_: t,
+                            substs: trait_substs,
+                        }));
+                        Some(substs)
+                    }
+                };
 
-        self.write_assoc_resolution(id, item);
-        Some((def, substs))
+                self.write_assoc_resolution(id, item);
+                Some((def, substs))
+            },
+        )
     }
 
     fn find_self_types(&self, def: &ValueNs, actual_def_ty: Ty) -> Option<Substs> {
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index eb69344f6..8c3d32d09 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -166,37 +166,78 @@ pub(crate) fn lookup_method(
     name: &Name,
     resolver: &Resolver,
 ) -> Option<(Ty, Function)> {
-    iterate_method_candidates(ty, db, resolver, Some(name), |ty, f| Some((ty.clone(), f)))
+    iterate_method_candidates(ty, db, resolver, Some(name), LookupMode::MethodCall, |ty, f| match f
+    {
+        AssocItem::Function(f) => Some((ty.clone(), f)),
+        _ => None,
+    })
+}
+
+/// Whether we're looking up a dotted method call (like `v.len()`) or a path
+/// (like `Vec::new`).
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum LookupMode {
+    /// Looking up a method call like `v.len()`: We only consider candidates
+    /// that have a `self` parameter, and do autoderef.
+    MethodCall,
+    /// Looking up a path like `Vec::new` or `Vec::default`: We consider all
+    /// candidates including associated constants, but don't do autoderef.
+    Path,
 }
 
 // This would be nicer if it just returned an iterator, but that runs into
 // lifetime problems, because we need to borrow temp `CrateImplBlocks`.
+// FIXME add a context type here?
 pub(crate) fn iterate_method_candidates<T>(
     ty: &Canonical<Ty>,
     db: &impl HirDatabase,
     resolver: &Resolver,
     name: Option<&Name>,
-    mut callback: impl FnMut(&Ty, Function) -> Option<T>,
+    mode: LookupMode,
+    mut callback: impl FnMut(&Ty, AssocItem) -> 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.
+    let krate = resolver.krate()?;
+    match mode {
+        LookupMode::MethodCall => {
+            // 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).
+            // 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 = resolver.krate()?;
-    for derefed_ty in autoderef::autoderef(db, resolver, ty.clone()) {
-        if let Some(result) = iterate_inherent_methods(&derefed_ty, db, name, krate, &mut callback)
-        {
-            return Some(result);
+            for derefed_ty in autoderef::autoderef(db, resolver, ty.clone()) {
+                if let Some(result) =
+                    iterate_inherent_methods(&derefed_ty, db, name, mode, krate, &mut callback)
+                {
+                    return Some(result);
+                }
+                if let Some(result) = iterate_trait_method_candidates(
+                    &derefed_ty,
+                    db,
+                    resolver,
+                    name,
+                    mode,
+                    &mut callback,
+                ) {
+                    return Some(result);
+                }
+            }
         }
-        if let Some(result) =
-            iterate_trait_method_candidates(&derefed_ty, db, resolver, name, &mut callback)
-        {
-            return Some(result);
+        LookupMode::Path => {
+            // No autoderef for path lookups
+            if let Some(result) =
+                iterate_inherent_methods(&ty, db, name, mode, krate, &mut callback)
+            {
+                return Some(result);
+            }
+            if let Some(result) =
+                iterate_trait_method_candidates(&ty, db, resolver, name, mode, &mut callback)
+            {
+                return Some(result);
+            }
         }
     }
     None
@@ -207,7 +248,8 @@ fn iterate_trait_method_candidates<T>(
     db: &impl HirDatabase,
     resolver: &Resolver,
     name: Option<&Name>,
-    mut callback: impl FnMut(&Ty, Function) -> Option<T>,
+    mode: LookupMode,
+    mut callback: impl FnMut(&Ty, AssocItem) -> Option<T>,
 ) -> Option<T> {
     let krate = resolver.krate()?;
     // FIXME: maybe put the trait_env behind a query (need to figure out good input parameters for that)
@@ -231,22 +273,20 @@ fn iterate_trait_method_candidates<T>(
         // trait, but if we find out it doesn't, we'll skip the rest of the
         // iteration
         let mut known_implemented = inherently_implemented;
-        for item in data.items() {
-            if let AssocItem::Function(m) = *item {
-                let data = m.data(db);
-                if name.map_or(true, |name| data.name() == name) && data.has_self_param() {
-                    if !known_implemented {
-                        let goal = generic_implements_goal(db, env.clone(), t, ty.clone());
-                        if db.trait_solve(krate, goal).is_none() {
-                            continue 'traits;
-                        }
-                    }
-                    known_implemented = true;
-                    if let Some(result) = callback(&ty.value, m) {
-                        return Some(result);
-                    }
+        for &item in data.items() {
+            if !is_valid_candidate(db, name, mode, item) {
+                continue;
+            }
+            if !known_implemented {
+                let goal = generic_implements_goal(db, env.clone(), t, ty.clone());
+                if db.trait_solve(krate, goal).is_none() {
+                    continue 'traits;
                 }
             }
+            known_implemented = true;
+            if let Some(result) = callback(&ty.value, item) {
+                return Some(result);
+            }
         }
     }
     None
@@ -256,21 +296,20 @@ fn iterate_inherent_methods<T>(
     ty: &Canonical<Ty>,
     db: &impl HirDatabase,
     name: Option<&Name>,
+    mode: LookupMode,
     krate: Crate,
-    mut callback: impl FnMut(&Ty, Function) -> Option<T>,
+    mut callback: impl FnMut(&Ty, AssocItem) -> Option<T>,
 ) -> Option<T> {
     for krate in def_crates(db, krate, &ty.value)? {
         let impls = db.impls_in_crate(krate);
 
         for impl_block in impls.lookup_impl_blocks(&ty.value) {
             for item in impl_block.items(db) {
-                if let AssocItem::Function(f) = item {
-                    let data = f.data(db);
-                    if name.map_or(true, |name| data.name() == name) && data.has_self_param() {
-                        if let Some(result) = callback(&ty.value, f) {
-                            return Some(result);
-                        }
-                    }
+                if !is_valid_candidate(db, name, mode, item) {
+                    continue;
+                }
+                if let Some(result) = callback(&ty.value, item) {
+                    return Some(result);
                 }
             }
         }
@@ -278,6 +317,26 @@ fn iterate_inherent_methods<T>(
     None
 }
 
+fn is_valid_candidate(
+    db: &impl HirDatabase,
+    name: Option<&Name>,
+    mode: LookupMode,
+    item: AssocItem,
+) -> bool {
+    match item {
+        AssocItem::Function(m) => {
+            let data = m.data(db);
+            name.map_or(true, |name| data.name() == name)
+                && (data.has_self_param() || mode == LookupMode::Path)
+        }
+        AssocItem::Const(c) => {
+            name.map_or(true, |name| Some(name) == c.name(db).as_ref())
+                && (mode == LookupMode::Path)
+        }
+        _ => false,
+    }
+}
+
 pub(crate) fn implements_trait(
     ty: &Canonical<Ty>,
     db: &impl HirDatabase,
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index c12326643..bfef48b16 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -1841,8 +1841,8 @@ fn test() {
     [243; 254) 'Struct::FOO': u32
     [264; 265) 'y': u32
     [268; 277) 'Enum::BAR': u32
-    [287; 288) 'z': {unknown}
-    [291; 304) 'TraitTest::ID': {unknown}
+    [287; 288) 'z': u32
+    [291; 304) 'TraitTest::ID': u32
     "###
     );
 }
@@ -2782,9 +2782,9 @@ fn test() {
     [97; 99) 's1': S
     [105; 121) 'Defaul...efault': fn default<S>() -> Self
     [105; 123) 'Defaul...ault()': S
-    [133; 135) 's2': {unknown}
-    [138; 148) 'S::default': {unknown}
-    [138; 150) 'S::default()': {unknown}
+    [133; 135) 's2': S
+    [138; 148) 'S::default': fn default<S>() -> Self
+    [138; 150) 'S::default()': S
     [160; 162) 's3': S
     [165; 188) '<S as ...efault': fn default<S>() -> Self
     [165; 190) '<S as ...ault()': S
@@ -2793,6 +2793,153 @@ fn test() {
 }
 
 #[test]
+fn infer_trait_assoc_method_generics_1() {
+    assert_snapshot!(
+        infer(r#"
+trait Trait<T> {
+    fn make() -> T;
+}
+struct S;
+impl Trait<u32> for S {}
+struct G<T>;
+impl<T> Trait<T> for G<T> {}
+fn test() {
+    let a = S::make();
+    let b = G::<u64>::make();
+    let c: f64 = G::make();
+}
+"#),
+        @r###"
+    [127; 211) '{     ...e(); }': ()
+    [137; 138) 'a': u32
+    [141; 148) 'S::make': fn make<S, u32>() -> T
+    [141; 150) 'S::make()': u32
+    [160; 161) 'b': u64
+    [164; 178) 'G::<u64>::make': fn make<G<u64>, u64>() -> T
+    [164; 180) 'G::<u6...make()': u64
+    [190; 191) 'c': f64
+    [199; 206) 'G::make': fn make<G<f64>, f64>() -> T
+    [199; 208) 'G::make()': f64
+    "###
+    );
+}
+
+#[test]
+fn infer_trait_assoc_method_generics_2() {
+    assert_snapshot!(
+        infer(r#"
+trait Trait<T> {
+    fn make<U>() -> (T, U);
+}
+struct S;
+impl Trait<u32> for S {}
+struct G<T>;
+impl<T> Trait<T> for G<T> {}
+fn test() {
+    let a = S::make::<i64>();
+    let b: (_, i64) = S::make();
+    let c = G::<u32>::make::<i64>();
+    let d: (u32, _) = G::make::<i64>();
+    let e: (u32, i64) = G::make();
+}
+"#),
+        @r###"
+    [135; 313) '{     ...e(); }': ()
+    [145; 146) 'a': (u32, i64)
+    [149; 163) 'S::make::<i64>': fn make<S, u32, i64>() -> (T, U)
+    [149; 165) 'S::mak...i64>()': (u32, i64)
+    [175; 176) 'b': (u32, i64)
+    [189; 196) 'S::make': fn make<S, u32, i64>() -> (T, U)
+    [189; 198) 'S::make()': (u32, i64)
+    [208; 209) 'c': (u32, i64)
+    [212; 233) 'G::<u3...:<i64>': fn make<G<u32>, u32, i64>() -> (T, U)
+    [212; 235) 'G::<u3...i64>()': (u32, i64)
+    [245; 246) 'd': (u32, i64)
+    [259; 273) 'G::make::<i64>': fn make<G<u32>, u32, i64>() -> (T, U)
+    [259; 275) 'G::mak...i64>()': (u32, i64)
+    [285; 286) 'e': (u32, i64)
+    [301; 308) 'G::make': fn make<G<u32>, u32, i64>() -> (T, U)
+    [301; 310) 'G::make()': (u32, i64)
+    "###
+    );
+}
+
+#[test]
+fn infer_trait_assoc_method_generics_3() {
+    assert_snapshot!(
+        infer(r#"
+trait Trait<T> {
+    fn make() -> (Self, T);
+}
+struct S<T>;
+impl Trait<i64> for S<i32> {}
+fn test() {
+    let a = S::make();
+}
+"#),
+        @r###"
+    [101; 127) '{     ...e(); }': ()
+    [111; 112) 'a': (S<i32>, i64)
+    [115; 122) 'S::make': fn make<S<i32>, i64>() -> (Self, T)
+    [115; 124) 'S::make()': (S<i32>, i64)
+    "###
+    );
+}
+
+#[test]
+fn infer_trait_assoc_method_generics_4() {
+    assert_snapshot!(
+        infer(r#"
+trait Trait<T> {
+    fn make() -> (Self, T);
+}
+struct S<T>;
+impl Trait<i64> for S<u64> {}
+impl Trait<i32> for S<u32> {}
+fn test() {
+    let a: (S<u64>, _) = S::make();
+    let b: (_, i32) = S::make();
+}
+"#),
+        @r###"
+    [131; 203) '{     ...e(); }': ()
+    [141; 142) 'a': (S<u64>, i64)
+    [158; 165) 'S::make': fn make<S<u64>, i64>() -> (Self, T)
+    [158; 167) 'S::make()': (S<u64>, i64)
+    [177; 178) 'b': (S<u32>, i32)
+    [191; 198) 'S::make': fn make<S<u32>, i32>() -> (Self, T)
+    [191; 200) 'S::make()': (S<u32>, i32)
+    "###
+    );
+}
+
+#[test]
+fn infer_trait_assoc_method_generics_5() {
+    assert_snapshot!(
+        infer(r#"
+trait Trait<T> {
+    fn make<U>() -> (Self, T, U);
+}
+struct S<T>;
+impl Trait<i64> for S<u64> {}
+fn test() {
+    let a = <S as Trait<i64>>::make::<u8>();
+    let b: (S<u64>, _, _) = Trait::<i64>::make::<u8>();
+}
+"#),
+        @r###"
+    [107; 211) '{     ...>(); }': ()
+    [117; 118) 'a': (S<u64>, i64, u8)
+    [121; 150) '<S as ...::<u8>': fn make<S<u64>, i64, u8>() -> (Self, T, U)
+    [121; 152) '<S as ...<u8>()': (S<u64>, i64, u8)
+    [162; 163) 'b': (S<u64>, i64, u8)
+    [182; 206) 'Trait:...::<u8>': fn make<S<u64>, i64, u8>() -> (Self, T, U)
+    [182; 208) 'Trait:...<u8>()': (S<u64>, i64, u8)
+    "###
+    );
+}
+
+#[test]
 fn infer_from_bound_1() {
     assert_snapshot!(
         infer(r#"
@@ -3303,6 +3450,22 @@ fn test() { S.foo()<|>; }
     assert_eq!(t, "u128");
 }
 
+#[ignore]
+#[test]
+fn method_resolution_by_value_before_autoref() {
+    let t = type_at(
+        r#"
+//- /main.rs
+trait Clone { fn clone(&self) -> Self; }
+struct S;
+impl Clone for S {}
+impl Clone for &S {}
+fn test() { (S.clone(), (&S).clone(), (&&S).clone())<|>; }
+"#,
+    );
+    assert_eq!(t, "(S, S, &S)");
+}
+
 #[test]
 fn method_resolution_trait_before_autoderef() {
     let t = type_at(