start cleaning up the resolution

Nameres related types, like `PerNs<Resolution>`, can represent
unreasonable situations, like a local in a type namespace. We should
clean this up, by requiring that call-site specifies the kind of
resolution it expects.

crates/ra_hir/src/expr/validation.rs

@@ -11,7 +11,7 @@ use crate::{
     name,
     path::{PathKind, PathSegment},
     ty::{ApplicationTy, InferenceResult, Ty, TypeCtor},
-    Function, ModuleDef, Name, Path, PerNs, Resolution,
+    Function, Name, Path,
 };
 
 use super::{Expr, ExprId, RecordLitField};
@@ -119,11 +119,10 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
         };
 
         let resolver = self.func.resolver(db);
-        let std_result_enum =
-            match resolver.resolve_path_segments(db, &std_result_path).into_fully_resolved() {
-                PerNs { types: Some(Resolution::Def(ModuleDef::Enum(e))), .. } => e,
-                _ => return,
-            };
+        let std_result_enum = match resolver.resolve_known_enum(db, &std_result_path) {
+            Some(it) => it,
+            _ => return,
+        };
 
         let std_result_ctor = TypeCtor::Adt(AdtDef::Enum(std_result_enum));
         let params = match &mismatch.expected {

crates/ra_hir/src/resolve.rs

@@ -15,7 +15,7 @@ use crate::{
     name::{Name, SELF_PARAM, SELF_TYPE},
     nameres::{CrateDefMap, CrateModuleId, PerNs},
     path::Path,
-    MacroDef, ModuleDef, Trait,
+    Enum, MacroDef, ModuleDef, Struct, Trait,
 };
 
 #[derive(Debug, Clone, Default)]
@@ -39,6 +39,8 @@ pub(crate) struct ExprScope {
 #[derive(Debug, Clone)]
 pub(crate) struct PathResult {
     /// The actual path resolution
+    // FIXME: `PerNs<Resolution>` type doesn't make sense, as not every
+    // Resolution variant can appear in every namespace
     resolution: PerNs<Resolution>,
     /// The first index in the path that we
     /// were unable to resolve.
@@ -113,6 +115,9 @@ pub(crate) enum Scope {
 pub enum Resolution {
     /// An item
     Def(ModuleDef),
+
+    // FIXME: there's no way we can syntactically confuse a local with generic
+    // param, so these two should not be members of the single enum
     /// A local binding (only value namespace)
     LocalBinding(PatId),
     /// A generic parameter
@@ -121,6 +126,37 @@ pub enum Resolution {
 }
 
 impl Resolver {
+    /// Resolve known trait from std, like `std::futures::Future`
+    pub(crate) fn resolve_known_trait(&self, db: &impl HirDatabase, path: &Path) -> Option<Trait> {
+        let res = self.resolve_path_segments(db, path).into_fully_resolved().take_types()?;
+        match res {
+            Resolution::Def(ModuleDef::Trait(it)) => Some(it),
+            _ => None,
+        }
+    }
+
+    /// Resolve known struct from std, like `std::boxed::Box`
+    pub(crate) fn resolve_known_struct(
+        &self,
+        db: &impl HirDatabase,
+        path: &Path,
+    ) -> Option<Struct> {
+        let res = self.resolve_path_segments(db, path).into_fully_resolved().take_types()?;
+        match res {
+            Resolution::Def(ModuleDef::Struct(it)) => Some(it),
+            _ => None,
+        }
+    }
+
+    /// Resolve known enum from std, like `std::result::Result`
+    pub(crate) fn resolve_known_enum(&self, db: &impl HirDatabase, path: &Path) -> Option<Enum> {
+        let res = self.resolve_path_segments(db, path).into_fully_resolved().take_types()?;
+        match res {
+            Resolution::Def(ModuleDef::Enum(it)) => Some(it),
+            _ => None,
+        }
+    }
+
     pub(crate) fn resolve_name(&self, db: &impl HirDatabase, name: &Name) -> PerNs<Resolution> {
         let mut resolution = PerNs::none();
         for scope in self.scopes.iter().rev() {

crates/ra_hir/src/source_binder.rs

@@ -29,7 +29,7 @@ use crate::{
     path::{PathKind, PathSegment},
     ty::method_resolution::implements_trait,
     AsName, AstId, Const, Crate, DefWithBody, Either, Enum, Function, HasBody, HirFileId, MacroDef,
-    Module, ModuleDef, Name, Path, PerNs, Resolution, Resolver, Static, Struct, Trait, Ty,
+    Module, Name, Path, PerNs, Resolver, Static, Struct, Trait, Ty,
 };
 
 /// Locates the module by `FileId`. Picks topmost module in the file.
@@ -426,11 +426,10 @@ impl SourceAnalyzer {
             ],
         };
 
-        let std_future_trait =
-            match self.resolver.resolve_path_segments(db, &std_future_path).into_fully_resolved() {
-                PerNs { types: Some(Resolution::Def(ModuleDef::Trait(trait_))), .. } => trait_,
-                _ => return false,
-            };
+        let std_future_trait = match self.resolver.resolve_known_trait(db, &std_future_path) {
+            Some(it) => it,
+            _ => return false,
+        };
 
         let krate = match self.resolver.krate() {
             Some(krate) => krate,

crates/ra_hir/src/ty/infer.rs

@@ -34,7 +34,7 @@ use super::{
 };
 use crate::{
     adt::VariantDef,
-    code_model::{ModuleDef::Trait, TypeAlias},
+    code_model::TypeAlias,
     db::HirDatabase,
     diagnostics::DiagnosticSink,
     expr::{
@@ -43,12 +43,9 @@ use crate::{
     },
     generics::{GenericParams, HasGenericParams},
     name,
-    nameres::{Namespace, PerNs},
+    nameres::Namespace,
     path::{GenericArg, GenericArgs, PathKind, PathSegment},
-    resolve::{
-        Resolution::{self, Def},
-        Resolver,
-    },
+    resolve::{Resolution, Resolver},
     ty::infer::diagnostics::InferenceDiagnostic,
     type_ref::{Mutability, TypeRef},
     AdtDef, ConstData, DefWithBody, FnData, Function, HasBody, ImplItem, ModuleDef, Name, Path,
@@ -1460,12 +1457,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             ],
         };
 
-        match self.resolver.resolve_path_segments(self.db, &into_iter_path).into_fully_resolved() {
-            PerNs { types: Some(Def(Trait(trait_))), .. } => {
-                Some(trait_.associated_type_by_name(self.db, &name::ITEM)?)
-            }
-            _ => None,
-        }
+        let trait_ = self.resolver.resolve_known_trait(self.db, &into_iter_path)?;
+        trait_.associated_type_by_name(self.db, &name::ITEM)
     }
 
     fn resolve_ops_try_ok(&self) -> Option<TypeAlias> {
@@ -1478,12 +1471,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             ],
         };
 
-        match self.resolver.resolve_path_segments(self.db, &ops_try_path).into_fully_resolved() {
-            PerNs { types: Some(Def(Trait(trait_))), .. } => {
-                Some(trait_.associated_type_by_name(self.db, &name::OK)?)
-            }
-            _ => None,
-        }
+        let trait_ = self.resolver.resolve_known_trait(self.db, &ops_try_path)?;
+        trait_.associated_type_by_name(self.db, &name::OK)
     }
 
     fn resolve_future_future_output(&self) -> Option<TypeAlias> {
@@ -1496,16 +1485,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             ],
         };
 
-        match self
-            .resolver
-            .resolve_path_segments(self.db, &future_future_path)
-            .into_fully_resolved()
-        {
-            PerNs { types: Some(Def(Trait(trait_))), .. } => {
-                Some(trait_.associated_type_by_name(self.db, &name::OUTPUT)?)
-            }
-            _ => None,
-        }
+        let trait_ = self.resolver.resolve_known_trait(self.db, &future_future_path)?;
+        trait_.associated_type_by_name(self.db, &name::OUTPUT)
     }
 
     fn resolve_boxed_box(&self) -> Option<AdtDef> {
@@ -1517,13 +1498,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 PathSegment { name: name::BOX_TYPE, args_and_bindings: None },
             ],
         };
-
-        match self.resolver.resolve_path_segments(self.db, &boxed_box_path).into_fully_resolved() {
-            PerNs { types: Some(Def(ModuleDef::Struct(struct_))), .. } => {
-                Some(AdtDef::Struct(struct_))
-            }
-            _ => None,
-        }
+        let struct_ = self.resolver.resolve_known_struct(self.db, &boxed_box_path)?;
+        Some(AdtDef::Struct(struct_))
     }
 }
 

crates/ra_hir/src/ty/lower.rs

@@ -86,7 +86,7 @@ impl Ty {
         }
     }
 
-    pub(crate) fn from_hir_path(db: &impl HirDatabase, resolver: &Resolver, path: &Path) -> Self {
+    pub(crate) fn from_hir_path(db: &impl HirDatabase, resolver: &Resolver, path: &Path) -> Ty {
         // Resolve the path (in type namespace)
         let (resolution, remaining_index) = resolver.resolve_path_segments(db, path).into_inner();
         let resolution = resolution.take_types();