Merge #2151

2151: Resolve (and complete) trait calls like `Vec::default()` r=flodiebold a=flodiebold

Similar to rustc, we do this using the same code as the method call resolution, just without doing autoderef (and considering more potential candidates).

(Btw, we currently don't complete methods with `self` in path notation, even though they'd be legal to use, so maybe we should -- on the other hand, that will usually not be the most interesting completions...)

Co-authored-by: Florian Diebold <[email protected]>

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(