Implement basic support for Associated Methods and Constants

This is done in `infer_path_expr`. When `Resolver::resolve_path` returns
`PartiallyResolved`, we use the returned `Resolution` together with the given
`segment_index` to check if we can find something matching the segment at
segment_index in the impls for that particular type.

crates/ra_hir/src/impl_block.rs

@@ -88,7 +88,7 @@ impl ImplBlock {
         if let Some(TypeRef::Path(path)) = self.target_trait_ref(db) {
             let resolver = self.resolver(db);
             if let Some(Resolution::Def(ModuleDef::Trait(tr))) =
-                resolver.resolve_path(db, &path).take_types()
+                resolver.resolve_path(db, &path).into_per_ns().take_types()
             {
                 return Some(tr);
             }

crates/ra_hir/src/nameres.rs

@@ -119,6 +119,10 @@ impl<T> PerNs<T> {
         self.types.is_some() && self.values.is_some()
     }
 
+    pub fn is_values(&self) -> bool {
+        self.values.is_some() && self.types.is_none()
+    }
+
     pub fn take(self, namespace: Namespace) -> Option<T> {
         match namespace {
             Namespace::Types => self.types,
@@ -297,7 +301,14 @@ where
             );
             (res, if res.is_none() { ReachedFixedPoint::No } else { ReachedFixedPoint::Yes })
         } else {
-            self.result.resolve_path_fp(self.db, ResolveMode::Import, original_module, &import.path)
+            let res = self.result.resolve_path_fp(
+                self.db,
+                ResolveMode::Import,
+                original_module,
+                &import.path,
+            );
+
+            (res.module, res.reached_fixedpoint)
         };
 
         if reached_fixedpoint != ReachedFixedPoint::Yes {
@@ -435,6 +446,27 @@ where
     }
 }
 
+#[derive(Debug, Clone)]
+pub struct ResolvePathResult {
+    pub(crate) module: PerNs<ModuleDef>,
+    pub(crate) segment_index: Option<usize>,
+    reached_fixedpoint: ReachedFixedPoint,
+}
+
+impl ResolvePathResult {
+    fn empty(reached_fixedpoint: ReachedFixedPoint) -> ResolvePathResult {
+        ResolvePathResult::with(PerNs::none(), reached_fixedpoint, None)
+    }
+
+    fn with(
+        module: PerNs<ModuleDef>,
+        reached_fixedpoint: ReachedFixedPoint,
+        segment_index: Option<usize>,
+    ) -> ResolvePathResult {
+        ResolvePathResult { module, reached_fixedpoint, segment_index }
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum ResolveMode {
     Import,
@@ -468,8 +500,9 @@ impl ItemMap {
         db: &impl PersistentHirDatabase,
         original_module: Module,
         path: &Path,
-    ) -> PerNs<ModuleDef> {
-        self.resolve_path_fp(db, ResolveMode::Other, original_module, path).0
+    ) -> (PerNs<ModuleDef>, Option<usize>) {
+        let res = self.resolve_path_fp(db, ResolveMode::Other, original_module, path);
+        (res.module, res.segment_index)
     }
 
     fn resolve_in_prelude(
@@ -534,7 +567,7 @@ impl ItemMap {
         mode: ResolveMode,
         original_module: Module,
         path: &Path,
-    ) -> (PerNs<ModuleDef>, ReachedFixedPoint) {
+    ) -> ResolvePathResult {
         let mut segments = path.segments.iter().enumerate();
         let mut curr_per_ns: PerNs<ModuleDef> = match path.kind {
             PathKind::Crate => PerNs::types(original_module.crate_root(db).into()),
@@ -549,7 +582,7 @@ impl ItemMap {
             {
                 let segment = match segments.next() {
                     Some((_, segment)) => segment,
-                    None => return (PerNs::none(), ReachedFixedPoint::Yes),
+                    None => return ResolvePathResult::empty(ReachedFixedPoint::Yes),
                 };
                 log::debug!("resolving {:?} in crate root (+ extern prelude)", segment);
                 self.resolve_name_in_crate_root_or_extern_prelude(
@@ -561,7 +594,7 @@ impl ItemMap {
             PathKind::Plain => {
                 let segment = match segments.next() {
                     Some((_, segment)) => segment,
-                    None => return (PerNs::none(), ReachedFixedPoint::Yes),
+                    None => return ResolvePathResult::empty(ReachedFixedPoint::Yes),
                 };
                 log::debug!("resolving {:?} in module", segment);
                 self.resolve_name_in_module(db, original_module, &segment.name)
@@ -571,20 +604,20 @@ impl ItemMap {
                     PerNs::types(p.into())
                 } else {
                     log::debug!("super path in root module");
-                    return (PerNs::none(), ReachedFixedPoint::Yes);
+                    return ResolvePathResult::empty(ReachedFixedPoint::Yes);
                 }
             }
             PathKind::Abs => {
                 // 2018-style absolute path -- only extern prelude
                 let segment = match segments.next() {
                     Some((_, segment)) => segment,
-                    None => return (PerNs::none(), ReachedFixedPoint::Yes),
+                    None => return ResolvePathResult::empty(ReachedFixedPoint::Yes),
                 };
                 if let Some(def) = self.extern_prelude.get(&segment.name) {
                     log::debug!("absolute path {:?} resolved to crate {:?}", path, def);
                     PerNs::types(*def)
                 } else {
-                    return (PerNs::none(), ReachedFixedPoint::No); // extern crate declarations can add to the extern prelude
+                    return ResolvePathResult::empty(ReachedFixedPoint::No); // extern crate declarations can add to the extern prelude
                 }
             }
         };
@@ -598,7 +631,7 @@ impl ItemMap {
                     // (don't break here because `curr_per_ns` might contain
                     // something in the value namespace, and it would be wrong
                     // to return that)
-                    return (PerNs::none(), ReachedFixedPoint::No);
+                    return ResolvePathResult::empty(ReachedFixedPoint::No);
                 }
             };
             // resolve segment in curr
@@ -612,15 +645,15 @@ impl ItemMap {
                         };
                         log::debug!("resolving {:?} in other crate", path);
                         let item_map = db.item_map(module.krate);
-                        let def = item_map.resolve_path(db, *module, &path);
-                        return (def, ReachedFixedPoint::Yes);
+                        let (def, s) = item_map.resolve_path(db, *module, &path);
+                        return ResolvePathResult::with(def, ReachedFixedPoint::Yes, s);
                     }
 
                     match self[module.module_id].items.get(&segment.name) {
                         Some(res) if !res.def.is_none() => res.def,
                         _ => {
                             log::debug!("path segment {:?} not found", segment.name);
-                            return (PerNs::none(), ReachedFixedPoint::No);
+                            return ResolvePathResult::empty(ReachedFixedPoint::No);
                         }
                     }
                 }
@@ -629,9 +662,22 @@ impl ItemMap {
                     tested_by!(item_map_enum_importing);
                     match e.variant(db, &segment.name) {
                         Some(variant) => PerNs::both(variant.into(), variant.into()),
-                        None => PerNs::none(),
+                        None => {
+                            return ResolvePathResult::with(
+                                PerNs::types((*e).into()),
+                                ReachedFixedPoint::Yes,
+                                Some(i),
+                            );
                         }
                     }
+                }
+                ModuleDef::Struct(s) => {
+                    return ResolvePathResult::with(
+                        PerNs::types((*s).into()),
+                        ReachedFixedPoint::Yes,
+                        Some(i),
+                    );
+                }
                 _ => {
                     // could be an inherent method call in UFCS form
                     // (`Struct::method`), or some other kind of associated
@@ -641,11 +687,11 @@ impl ItemMap {
                         segment.name,
                         curr,
                     );
-                    return (PerNs::none(), ReachedFixedPoint::Yes);
+                    return ResolvePathResult::empty(ReachedFixedPoint::Yes);
                 }
             };
         }
-        (curr_per_ns, ReachedFixedPoint::Yes)
+        ResolvePathResult::with(curr_per_ns, ReachedFixedPoint::Yes, None)
     }
 }
 

crates/ra_hir/src/resolve.rs

@@ -32,6 +32,32 @@ pub(crate) struct ExprScope {
     scope_id: ScopeId,
 }
 
+#[derive(Debug, Clone)]
+pub enum PathResult {
+    /// Path was fully resolved
+    FullyResolved(PerNs<Resolution>),
+    /// Path was partially resolved, first element contains the resolution
+    /// second contains the index in the Path.segments which we were unable to resolve
+    PartiallyResolved(PerNs<Resolution>, usize),
+}
+
+impl PathResult {
+    pub fn segment_index(&self) -> Option<usize> {
+        match self {
+            PathResult::FullyResolved(_) => None,
+            PathResult::PartiallyResolved(_, ref i) => Some(*i),
+        }
+    }
+
+    /// Consumes `PathResult` and returns the contained `PerNs<Resolution>`
+    pub fn into_per_ns(self) -> PerNs<Resolution> {
+        match self {
+            PathResult::FullyResolved(def) => def,
+            PathResult::PartiallyResolved(def, _) => def,
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub(crate) enum Scope {
     /// All the items and imported names of a module
@@ -67,18 +93,26 @@ impl Resolver {
         resolution
     }
 
-    pub fn resolve_path(&self, db: &impl HirDatabase, path: &Path) -> PerNs<Resolution> {
+    pub fn resolve_path(&self, db: &impl HirDatabase, path: &Path) -> PathResult {
+        use self::PathResult::*;
         if let Some(name) = path.as_ident() {
-            self.resolve_name(db, name)
+            FullyResolved(self.resolve_name(db, name))
         } else if path.is_self() {
-            self.resolve_name(db, &Name::self_param())
+            FullyResolved(self.resolve_name(db, &Name::self_param()))
         } else {
             let (item_map, module) = match self.module() {
                 Some(m) => m,
-                _ => return PerNs::none(),
+                _ => return FullyResolved(PerNs::none()),
             };
-            let module_res = item_map.resolve_path(db, module, path);
-            module_res.map(Resolution::Def)
+            let (module_res, segment_index) = item_map.resolve_path(db, module, path);
+
+            let def = module_res.map(Resolution::Def);
+
+            if let Some(index) = segment_index {
+                PartiallyResolved(def, index)
+            } else {
+                FullyResolved(def)
+            }
         }
     }
 

crates/ra_hir/src/ty.rs

@@ -32,17 +32,20 @@ use rustc_hash::FxHashMap;
 
 use test_utils::tested_by;
 
+use ra_syntax::ast::NameOwner;
+
 use crate::{
     Function, Struct, StructField, Enum, EnumVariant, Path, Name,
+    Const,
     FnSignature, ModuleDef, AdtDef,
     HirDatabase,
     type_ref::{TypeRef, Mutability},
-    name::KnownName,
+    name::{KnownName, AsName},
     expr::{Body, Expr, BindingAnnotation, Literal, ExprId, Pat, PatId, UnaryOp, BinaryOp, Statement, FieldPat, self},
     generics::GenericParams,
     path::GenericArg,
     adt::VariantDef,
-    resolve::{Resolver, Resolution}, nameres::Namespace
+    resolve::{Resolver, Resolution, PathResult}, nameres::Namespace
 };
 
 /// The ID of a type variable.
@@ -370,7 +373,7 @@ impl Ty {
         }
 
         // Resolve the path (in type namespace)
-        let resolution = resolver.resolve_path(db, path).take_types();
+        let resolution = resolver.resolve_path(db, path).into_per_ns().take_types();
 
         let def = match resolution {
             Some(Resolution::Def(def)) => def,
@@ -678,6 +681,19 @@ fn type_for_fn(db: &impl HirDatabase, def: Function) -> Ty {
     Ty::FnDef { def: def.into(), sig, name, substs }
 }
 
+fn type_for_const(db: &impl HirDatabase, resolver: &Resolver, def: Const) -> Ty {
+    let node = def.source(db).1;
+
+    let tr = node
+        .type_ref()
+        .map(TypeRef::from_ast)
+        .as_ref()
+        .map(|tr| Ty::from_hir(db, resolver, tr))
+        .unwrap_or_else(|| Ty::Unknown);
+
+    tr
+}
+
 /// Compute the type of a tuple struct constructor.
 fn type_for_struct_constructor(db: &impl HirDatabase, def: Struct) -> Ty {
     let var_data = def.variant_data(db);
@@ -1172,16 +1188,57 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     }
 
     fn infer_path_expr(&mut self, resolver: &Resolver, path: &Path) -> Option<Ty> {
-        let resolved = resolver.resolve_path(self.db, &path).take_values()?;
+        let resolved = resolver.resolve_path(self.db, &path);
+
+        let (resolved, segment_index) = match resolved {
+            PathResult::FullyResolved(def) => (def.take_values()?, None),
+            PathResult::PartiallyResolved(def, index) => (def.take_types()?, Some(index)),
+        };
+
         match resolved {
             Resolution::Def(def) => {
                 let typable: Option<TypableDef> = def.into();
                 let typable = typable?;
+
+                if let Some(segment_index) = segment_index {
+                    let ty = self.db.type_for_def(typable, Namespace::Types);
+                    // TODO: What to do if segment_index is not the last segment
+                    // in the path
+                    let segment = &path.segments[segment_index];
+
+                    // Attempt to find an impl_item for the type which has a name matching
+                    // the current segment
+                    let ty = ty.iterate_impl_items(self.db, |item| match item {
+                        crate::ImplItem::Method(func) => {
+                            let sig = func.signature(self.db);
+                            if segment.name == *sig.name() {
+                                return Some(type_for_fn(self.db, func));
+                            }
+                            None
+                        }
+                        crate::ImplItem::Const(c) => {
+                            let node = c.source(self.db).1;
+
+                            if let Some(name) = node.name().map(|n| n.as_name()) {
+                                if segment.name == name {
+                                    return Some(type_for_const(self.db, resolver, c));
+                                }
+                            }
+
+                            None
+                        }
+
+                        // TODO: Resolve associated types
+                        crate::ImplItem::Type(_) => None,
+                    });
+                    ty
+                } else {
                     let substs = Ty::substs_from_path(self.db, &self.resolver, path, typable);
                     let ty = self.db.type_for_def(typable, Namespace::Values).apply_substs(substs);
                     let ty = self.insert_type_vars(ty);
                     Some(ty)
                 }
+            }
             Resolution::LocalBinding(pat) => {
                 let ty = self.type_of_pat.get(pat)?;
                 let ty = self.resolve_ty_as_possible(&mut vec![], ty.clone());
@@ -1204,7 +1261,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             None => return (Ty::Unknown, None),
         };
         let resolver = &self.resolver;
-        let typable: Option<TypableDef> = match resolver.resolve_path(self.db, &path).take_types() {
+        let typable: Option<TypableDef> =
+            match resolver.resolve_path(self.db, &path).into_per_ns().take_types() {
                 Some(Resolution::Def(def)) => def.into(),
                 Some(Resolution::LocalBinding(..)) => {
                     // this cannot happen

crates/ra_hir/src/ty/snapshots/tests__infer_associated_const.snap

@@ -0,0 +1,14 @@
+---
+created: "2019-02-20T11:04:56.553382800Z"
+creator: insta@0.6.3
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[227; 305) '{     ...:ID; }': ()
+[237; 238) 'x': u32
+[241; 252) 'Struct::FOO': u32
+[262; 263) 'y': u32
+[266; 275) 'Enum::BAR': u32
+[285; 286) 'z': u32
+[289; 302) 'TraitTest::ID': u32
+

crates/ra_hir/src/ty/snapshots/tests__infer_associated_method_enum.snap

@@ -0,0 +1,20 @@
+---
+created: "2019-02-20T11:04:56.553382800Z"
+creator: insta@0.6.3
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[48; 68) '{     ...     }': A
+[58; 62) 'A::B': A
+[89; 109) '{     ...     }': A
+[99; 103) 'A::C': A
+[122; 179) '{     ...  c; }': ()
+[132; 133) 'a': A
+[136; 140) 'A::b': fn b() -> A
+[136; 142) 'A::b()': A
+[148; 149) 'a': A
+[159; 160) 'c': A
+[163; 167) 'A::c': fn c() -> A
+[163; 169) 'A::c()': A
+[175; 176) 'c': A
+

crates/ra_hir/src/ty/snapshots/tests__infer_associated_method_generics.snap

@@ -0,0 +1,16 @@
+---
+created: "2019-02-21T10:25:18.568887300Z"
+creator: insta@0.6.3
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[64; 67) 'val': T
+[82; 109) '{     ...     }': Gen<T>
+[92; 103) 'Gen { val }': Gen<T>
+[98; 101) 'val': T
+[123; 155) '{     ...32); }': ()
+[133; 134) 'a': Gen<[unknown]>
+[137; 146) 'Gen::make': fn make<[unknown]>(T) -> Gen<T>
+[137; 152) 'Gen::make(0u32)': Gen<[unknown]>
+[147; 151) '0u32': u32
+

crates/ra_hir/src/ty/snapshots/tests__infer_associated_method_struct.snap

@@ -0,0 +1,16 @@
+---
+created: "2019-02-20T11:04:56.553382800Z"
+creator: insta@0.6.3
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[50; 76) '{     ...     }': A
+[60; 70) 'A { x: 0 }': A
+[67; 68) '0': u32
+[89; 123) '{     ...a.x; }': ()
+[99; 100) 'a': A
+[103; 109) 'A::new': fn new() -> A
+[103; 111) 'A::new()': A
+[117; 118) 'a': A
+[117; 120) 'a.x': u32
+

crates/ra_hir/src/ty/snapshots/tests__infer_associated_method_with_modules.snap

@@ -0,0 +1,23 @@
+---
+created: "2019-02-21T08:55:53.926725400Z"
+creator: insta@0.6.3
+source: crates/ra_hir/src/ty/tests.rs
+expression: "&result"
+---
+[56; 64) '{ A {} }': A
+[58; 62) 'A {}': A
+[126; 132) '{ 99 }': u32
+[128; 130) '99': u32
+[202; 210) '{ C {} }': C
+[204; 208) 'C {}': C
+[241; 325) '{     ...g(); }': ()
+[251; 252) 'x': A
+[255; 266) 'a::A::thing': fn thing() -> A
+[255; 268) 'a::A::thing()': A
+[278; 279) 'y': u32
+[282; 293) 'b::B::thing': fn thing() -> u32
+[282; 295) 'b::B::thing()': u32
+[305; 306) 'z': C
+[309; 320) 'c::C::thing': fn thing() -> C
+[309; 322) 'c::C::thing()': C
+

crates/ra_hir/src/ty/tests.rs

@@ -586,6 +586,139 @@ fn test() -> i128 {
     );
 }
 
+#[test]
+fn infer_associated_const() {
+    check_inference(
+        "infer_associated_const",
+        r#"
+struct Struct;
+
+impl Struct {
+    const FOO: u32 = 1;
+}
+
+enum Enum;
+
+impl Enum {
+    const BAR: u32 = 2;
+}
+
+trait Trait {
+    const ID: u32;
+}
+
+struct TraitTest;
+
+impl Trait for TraitTest {
+    const ID: u32 = 5;
+}
+
+fn test() {
+    let x = Struct::FOO;
+    let y = Enum::BAR;
+    let z = TraitTest::ID;
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_associated_method_struct() {
+    check_inference(
+        "infer_associated_method_struct",
+        r#"
+struct A { x: u32 };
+
+impl A {
+    fn new() -> A {
+        A { x: 0 }
+    }
+}
+fn test() {
+    let a = A::new();
+    a.x;
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_associated_method_enum() {
+    check_inference(
+        "infer_associated_method_enum",
+        r#"
+enum A { B, C };
+
+impl A {
+    pub fn b() -> A {
+        A::B
+    }
+    pub fn c() -> A {
+        A::C
+    }
+}
+fn test() {
+    let a = A::b();
+    a;
+    let c = A::c();
+    c;
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_associated_method_with_modules() {
+    check_inference(
+        "infer_associated_method_with_modules",
+        r#"
+mod a {
+    struct A;
+    impl A { pub fn thing() -> A { A {} }}
+}
+
+mod b {
+    struct B;
+    impl B { pub fn thing() -> u32 { 99 }}
+
+    mod c {
+        struct C;
+        impl C { pub fn thing() -> C { C {} }}
+    }
+}
+use b::c;
+
+fn test() {
+    let x = a::A::thing();
+    let y = b::B::thing();
+    let z = c::C::thing();
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_associated_method_generics() {
+    check_inference(
+        "infer_associated_method_generics",
+        r#"
+struct Gen<T> {
+    val: T
+}
+
+impl<T> Gen<T> {
+    pub fn make(val: T) -> Gen<T> {
+        Gen { val }
+    }
+}
+
+fn test() {
+    let a = Gen::make(0u32);
+}
+"#,
+    );
+}
+
 #[test]
 fn no_panic_on_field_of_enum() {
     check_inference(

crates/ra_ide_api/src/completion/complete_path.rs

@@ -10,7 +10,7 @@ pub(super) fn complete_path(acc: &mut Completions, ctx: &CompletionContext) {
         Some(path) => path.clone(),
         _ => return,
     };
-    let def = match ctx.resolver.resolve_path(ctx.db, &path).take_types() {
+    let def = match ctx.resolver.resolve_path(ctx.db, &path).into_per_ns().take_types() {
         Some(Resolution::Def(def)) => def,
         _ => return,
     };

crates/ra_ide_api/src/goto_definition.rs

@@ -79,7 +79,7 @@ pub(crate) fn reference_definition(
     if let Some(path) =
         name_ref.syntax().ancestors().find_map(ast::Path::cast).and_then(hir::Path::from_ast)
     {
-        let resolved = resolver.resolve_path(db, &path);
+        let resolved = resolver.resolve_path(db, &path).into_per_ns();
         match resolved.clone().take_types().or_else(|| resolved.take_values()) {
             Some(Resolution::Def(def)) => return Exact(NavigationTarget::from_def(db, def)),
             Some(Resolution::LocalBinding(pat)) => {

crates/ra_ide_api/src/hover.rs

@@ -223,4 +223,24 @@ mod tests {
         assert_eq!("usize", &type_name);
     }
 
+    #[test]
+    fn test_hover_infer_associated_method_result() {
+        let (analysis, position) = single_file_with_position(
+            "
+            struct Thing { x: u32 };
+
+            impl Thing {
+                fn new() -> Thing {
+                    Thing { x: 0 }
+                }
+            }
+
+            fn main() {
+                let foo_<|>test = Thing::new();
+            }
+            ",
+        );
+        let hover = analysis.hover(position).unwrap().unwrap();
+        assert_eq!(hover.info, "Thing");
+    }
 }