Implement beginnings of generics

 - add HIR for generic params
 - resolve generic params in type paths
 - add substitions for ADTs
 - insert type variables for substitutions

13 files changed, 288 insertions, 82 deletions

diff --git a/crates/ra_hir/src/adt.rs b/crates/ra_hir/src/adt.rs
index d87fe7049..ab1c428db 100644
--- a/crates/ra_hir/src/adt.rs
+++ b/crates/ra_hir/src/adt.rs
@@ -1,3 +1,6 @@
+//! This module contains the implementation details of the HIR for ADTs, i.e.
+//! structs and enums (and unions).
+
 use std::sync::Arc;
 
 use ra_syntax::{
@@ -62,7 +65,7 @@ fn get_def_id(
     };
     let loc = DefLoc {
         kind: expected_kind,
-        source_item_id: source_item_id,
+        source_item_id,
         ..*same_file_loc
     };
     loc.id(db)
diff --git a/crates/ra_hir/src/code_model_api.rs b/crates/ra_hir/src/code_model_api.rs
index 11e919c1a..6c85e5939 100644
--- a/crates/ra_hir/src/code_model_api.rs
+++ b/crates/ra_hir/src/code_model_api.rs
@@ -12,6 +12,7 @@ use crate::{
     expr::BodySyntaxMapping,
     ty::InferenceResult,
     adt::VariantData,
+    generics::Generics,
     code_model_impl::def_id_to_ast,
 };
 
@@ -201,6 +202,10 @@ impl Struct {
     pub fn source(&self, db: &impl HirDatabase) -> (HirFileId, TreeArc<ast::StructDef>) {
         def_id_to_ast(db, self.def_id)
     }
+
+    pub fn generics(&self, db: &impl HirDatabase) -> Arc<Generics> {
+        db.generics(self.def_id)
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -228,6 +233,10 @@ impl Enum {
     pub fn source(&self, db: &impl HirDatabase) -> (HirFileId, TreeArc<ast::EnumDef>) {
         def_id_to_ast(db, self.def_id)
     }
+
+    pub fn generics(&self, db: &impl HirDatabase) -> Arc<Generics> {
+        db.generics(self.def_id)
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -339,6 +348,10 @@ impl Function {
     pub fn infer(&self, db: &impl HirDatabase) -> Arc<InferenceResult> {
         db.infer(self.def_id)
     }
+
+    pub fn generics(&self, db: &impl HirDatabase) -> Arc<Generics> {
+        db.generics(self.def_id)
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -384,6 +397,10 @@ impl Trait {
     pub fn source(&self, db: &impl HirDatabase) -> (HirFileId, TreeArc<ast::TraitDef>) {
         def_id_to_ast(db, self.def_id)
     }
+
+    pub fn generics(&self, db: &impl HirDatabase) -> Arc<Generics> {
+        db.generics(self.def_id)
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -399,4 +416,8 @@ impl Type {
     pub fn source(&self, db: &impl HirDatabase) -> (HirFileId, TreeArc<ast::TypeDef>) {
         def_id_to_ast(db, self.def_id)
     }
+
+    pub fn generics(&self, db: &impl HirDatabase) -> Arc<Generics> {
+        db.generics(self.def_id)
+    }
 }
diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 60065cf6a..10e64f880 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -14,6 +14,7 @@ use crate::{
     ty::{InferenceResult, Ty, method_resolution::CrateImplBlocks},
     adt::{StructData, EnumData, EnumVariantData},
     impl_block::ModuleImplBlocks,
+    generics::Generics,
 };
 
 #[salsa::query_group]
@@ -101,6 +102,9 @@ pub trait HirDatabase:
     #[salsa::invoke(crate::expr::body_syntax_mapping)]
     fn body_syntax_mapping(&self, def_id: DefId) -> Arc<crate::expr::BodySyntaxMapping>;
 
+    #[salsa::invoke(crate::generics::Generics::generics_query)]
+    fn generics(&self, def_id: DefId) -> Arc<Generics>;
+
     #[salsa::invoke(crate::FnSignature::fn_signature_query)]
     fn fn_signature(&self, def_id: DefId) -> Arc<FnSignature>;
 }
diff --git a/crates/ra_hir/src/generics.rs b/crates/ra_hir/src/generics.rs
new file mode 100644
index 000000000..cdabc0424
--- /dev/null
+++ b/crates/ra_hir/src/generics.rs
@@ -0,0 +1,48 @@
+//! Many kinds of items or constructs can have generic parameters: functions,
+//! structs, impls, traits, etc. This module provides a common HIR for these
+//! generic parameters. See also the `Generics` type and the `generics_of` query
+//! in rustc.
+
+use std::sync::Arc;
+
+use ra_syntax::ast::{TypeParamList, AstNode, NameOwner};
+
+use crate::{db::HirDatabase, DefId, Name, AsName};
+
+/// Data about a generic parameter (to a function, struct, impl, ...).
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct GenericParam {
+    pub(crate) idx: u32,
+    pub(crate) name: Name,
+}
+
+/// Data about the generic parameters of a function, struct, impl, etc.
+#[derive(Clone, PartialEq, Eq, Debug, Default)]
+pub struct Generics {
+    pub(crate) params: Vec<GenericParam>,
+}
+
+impl Generics {
+    pub(crate) fn generics_query(db: &impl HirDatabase, def_id: DefId) -> Arc<Generics> {
+        let (_file_id, node) = def_id.source(db);
+        let mut generics = Generics::default();
+        if let Some(type_param_list) = node.children().find_map(TypeParamList::cast) {
+            for (idx, type_param) in type_param_list.type_params().enumerate() {
+                let name = type_param
+                    .name()
+                    .map(AsName::as_name)
+                    .unwrap_or_else(Name::missing);
+                let param = GenericParam {
+                    idx: idx as u32,
+                    name,
+                };
+                generics.params.push(param);
+            }
+        }
+        Arc::new(generics)
+    }
+
+    pub(crate) fn find_by_name(&self, name: &Name) -> Option<&GenericParam> {
+        self.params.iter().find(|p| &p.name == name)
+    }
+}
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index f1402a286..361d39f03 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -24,6 +24,7 @@ mod type_ref;
 mod ty;
 mod impl_block;
 mod expr;
+mod generics;
 
 mod code_model_api;
 mod code_model_impl;
diff --git a/crates/ra_hir/src/mock.rs b/crates/ra_hir/src/mock.rs
index 018e5e0d4..d674db8e6 100644
--- a/crates/ra_hir/src/mock.rs
+++ b/crates/ra_hir/src/mock.rs
@@ -243,6 +243,7 @@ salsa::database_storage! {
             fn body_hir() for db::BodyHirQuery;
             fn body_syntax_mapping() for db::BodySyntaxMappingQuery;
             fn fn_signature() for db::FnSignatureQuery;
+            fn generics() for db::GenericsQuery;
         }
     }
 }
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index 8d6493887..b9a48929d 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -37,6 +37,7 @@ use crate::{
     type_ref::{TypeRef, Mutability},
     name::KnownName,
     expr::{Body, Expr, BindingAnnotation, Literal, ExprId, Pat, PatId, UnaryOp, BinaryOp, Statement, FieldPat},
+    generics::Generics,
 };
 
 /// The ID of a type variable.
@@ -151,10 +152,14 @@ impl Expectation {
     }
 }
 
+/// A list of substitutions for generic parameters.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct Substs(Arc<[Ty]>);
+
 /// A type. This is based on the `TyKind` enum in rustc (librustc/ty/sty.rs).
 ///
 /// This should be cheap to clone.
-#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug)]
 pub enum Ty {
     /// The primitive boolean type. Written as `bool`.
     Bool,
@@ -175,7 +180,8 @@ pub enum Ty {
         def_id: DefId,
         /// The name, for displaying.
         name: Name,
-        // later we'll need generic substitutions here
+        /// Substitutions for the generic parameters of the type.
+        substs: Substs,
     },
 
     /// The pointee of a string slice. Written as `str`.
@@ -234,9 +240,14 @@ pub enum Ty {
 
     // Opaque (`impl Trait`) type found in a return type.
     // Opaque(DefId, Substs),
+    /// A type parameter; for example, `T` in `fn f<T>(x: T) {}
+    Param {
+        /// The index of the parameter.
+        idx: u32,
+        /// The name of the parameter, for displaying.
+        name: Name,
+    },
 
-    // A type parameter; for example, `T` in `fn f<T>(x: T) {}
-    // Param(ParamTy),
     /// A type variable used during type checking. Not to be confused with a
     /// type parameter.
     Infer(InferTy),
@@ -250,7 +261,7 @@ pub enum Ty {
 }
 
 /// A function signature.
-#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug)]
 pub struct FnSig {
     input: Vec<Ty>,
     output: Ty,
@@ -261,6 +272,7 @@ impl Ty {
         db: &impl HirDatabase,
         module: &Module,
         impl_block: Option<&ImplBlock>,
+        generics: &Generics,
         type_ref: &TypeRef,
     ) -> Self {
         match type_ref {
@@ -268,32 +280,32 @@ impl Ty {
             TypeRef::Tuple(inner) => {
                 let inner_tys = inner
                     .iter()
-                    .map(|tr| Ty::from_hir(db, module, impl_block, tr))
+                    .map(|tr| Ty::from_hir(db, module, impl_block, generics, tr))
                     .collect::<Vec<_>>();
                 Ty::Tuple(inner_tys.into())
             }
-            TypeRef::Path(path) => Ty::from_hir_path(db, module, impl_block, path),
+            TypeRef::Path(path) => Ty::from_hir_path(db, module, impl_block, generics, path),
             TypeRef::RawPtr(inner, mutability) => {
-                let inner_ty = Ty::from_hir(db, module, impl_block, inner);
+                let inner_ty = Ty::from_hir(db, module, impl_block, generics, inner);
                 Ty::RawPtr(Arc::new(inner_ty), *mutability)
             }
             TypeRef::Array(inner) => {
-                let inner_ty = Ty::from_hir(db, module, impl_block, inner);
+                let inner_ty = Ty::from_hir(db, module, impl_block, generics, inner);
                 Ty::Array(Arc::new(inner_ty))
             }
             TypeRef::Slice(inner) => {
-                let inner_ty = Ty::from_hir(db, module, impl_block, inner);
+                let inner_ty = Ty::from_hir(db, module, impl_block, generics, inner);
                 Ty::Slice(Arc::new(inner_ty))
             }
             TypeRef::Reference(inner, mutability) => {
-                let inner_ty = Ty::from_hir(db, module, impl_block, inner);
+                let inner_ty = Ty::from_hir(db, module, impl_block, generics, inner);
                 Ty::Ref(Arc::new(inner_ty), *mutability)
             }
             TypeRef::Placeholder => Ty::Unknown,
             TypeRef::Fn(params) => {
                 let mut inner_tys = params
                     .iter()
-                    .map(|tr| Ty::from_hir(db, module, impl_block, tr))
+                    .map(|tr| Ty::from_hir(db, module, impl_block, generics, tr))
                     .collect::<Vec<_>>();
                 let return_ty = inner_tys
                     .pop()
@@ -312,15 +324,19 @@ impl Ty {
         db: &impl HirDatabase,
         module: &Module,
         impl_block: Option<&ImplBlock>,
+        generics: &Generics,
         type_ref: Option<&TypeRef>,
     ) -> Self {
-        type_ref.map_or(Ty::Unknown, |t| Ty::from_hir(db, module, impl_block, t))
+        type_ref.map_or(Ty::Unknown, |t| {
+            Ty::from_hir(db, module, impl_block, generics, t)
+        })
     }
 
     pub(crate) fn from_hir_path(
         db: &impl HirDatabase,
         module: &Module,
         impl_block: Option<&ImplBlock>,
+        generics: &Generics,
         path: &Path,
     ) -> Self {
         if let Some(name) = path.as_ident() {
@@ -329,7 +345,15 @@ impl Ty {
             } else if let Some(float_ty) = primitive::UncertainFloatTy::from_name(name) {
                 return Ty::Float(float_ty);
             } else if name.as_known_name() == Some(KnownName::SelfType) {
-                return Ty::from_hir_opt(db, module, None, impl_block.map(|i| i.target_type()));
+                // TODO pass the impl block's generics?
+                let generics = &Generics::default();
+                return Ty::from_hir_opt(
+                    db,
+                    module,
+                    None,
+                    generics,
+                    impl_block.map(|i| i.target_type()),
+                );
             } else if let Some(known) = name.as_known_name() {
                 match known {
                     KnownName::Bool => return Ty::Bool,
@@ -337,6 +361,11 @@ impl Ty {
                     KnownName::Str => return Ty::Str,
                     _ => {}
                 }
+            } else if let Some(generic_param) = generics.find_by_name(&name) {
+                return Ty::Param {
+                    idx: generic_param.idx,
+                    name: generic_param.name.clone(),
+                };
             }
         }
 
@@ -374,7 +403,14 @@ impl Ty {
                 }
                 sig_mut.output.walk_mut(f);
             }
-            Ty::Adt { .. } => {} // need to walk type parameters later
+            Ty::Adt { substs, .. } => {
+                // Without an Arc::make_mut_slice, we can't avoid the clone here:
+                let mut v: Vec<_> = substs.0.iter().cloned().collect();
+                for t in &mut v {
+                    t.walk_mut(f);
+                }
+                substs.0 = v.into();
+            }
             _ => {}
         }
     }
@@ -394,6 +430,32 @@ impl Ty {
             _ => None,
         }
     }
+
+    /// Replaces type parameters in this type using the given `Substs`. (So e.g.
+    /// if `self` is `&[T]`, where type parameter T has index 0, and the
+    /// `Substs` contain `u32` at index 0, we'll have `&[u32]` afterwards.)
+    pub fn subst(self, substs: &Substs) -> Ty {
+        self.fold(&mut |ty| match ty {
+            Ty::Param { idx, name } => {
+                if (idx as usize) < substs.0.len() {
+                    substs.0[idx as usize].clone()
+                } else {
+                    // TODO it's yet unclear to me whether we need to shift the indices here
+                    Ty::Param { idx, name }
+                }
+            }
+            ty => ty,
+        })
+    }
+
+    /// Returns the type parameters of this type if it has some (i.e. is an ADT
+    /// or function); so if `self` is `Option<u32>`, this returns the `u32`.
+    fn substs(&self) -> Option<Substs> {
+        match self {
+            Ty::Adt { substs, .. } => Some(substs.clone()),
+            _ => None,
+        }
+    }
 }
 
 impl fmt::Display for Ty {
@@ -425,7 +487,17 @@ impl fmt::Display for Ty {
                     .to_fmt(f)?;
                 write!(f, " -> {}", sig.output)
             }
-            Ty::Adt { name, .. } => write!(f, "{}", name),
+            Ty::Adt { name, substs, .. } => {
+                write!(f, "{}", name)?;
+                if substs.0.len() > 0 {
+                    join(substs.0.iter())
+                        .surround_with("<", ">")
+                        .separator(", ")
+                        .to_fmt(f)?;
+                }
+                Ok(())
+            }
+            Ty::Param { name, .. } => write!(f, "{}", name),
             Ty::Unknown => write!(f, "[unknown]"),
             Ty::Infer(..) => write!(f, "_"),
         }
@@ -440,28 +512,49 @@ fn type_for_fn(db: &impl HirDatabase, f: Function) -> Ty {
     let signature = f.signature(db);
     let module = f.module(db);
     let impl_block = f.impl_block(db);
-    // TODO we ignore type parameters for now
+    let generics = f.generics(db);
     let input = signature
         .params()
         .iter()
-        .map(|tr| Ty::from_hir(db, &module, impl_block.as_ref(), tr))
+        .map(|tr| Ty::from_hir(db, &module, impl_block.as_ref(), &generics, tr))
         .collect::<Vec<_>>();
-    let output = Ty::from_hir(db, &module, impl_block.as_ref(), signature.ret_type());
+    let output = Ty::from_hir(
+        db,
+        &module,
+        impl_block.as_ref(),
+        &generics,
+        signature.ret_type(),
+    );
     let sig = FnSig { input, output };
     Ty::FnPtr(Arc::new(sig))
 }
 
+fn make_substs(generics: &Generics) -> Substs {
+    Substs(
+        generics
+            .params
+            .iter()
+            .map(|_p| Ty::Unknown)
+            .collect::<Vec<_>>()
+            .into(),
+    )
+}
+
 fn type_for_struct(db: &impl HirDatabase, s: Struct) -> Ty {
+    let generics = s.generics(db);
     Ty::Adt {
         def_id: s.def_id(),
         name: s.name(db).unwrap_or_else(Name::missing),
+        substs: make_substs(&generics),
     }
 }
 
 pub(crate) fn type_for_enum(db: &impl HirDatabase, s: Enum) -> Ty {
+    let generics = s.generics(db);
     Ty::Adt {
         def_id: s.def_id(),
         name: s.name(db).unwrap_or_else(Name::missing),
+        substs: make_substs(&generics),
     }
 }
 
@@ -506,8 +599,15 @@ pub(super) fn type_for_field(db: &impl HirDatabase, def_id: DefId, field: Name)
     };
     let module = def_id.module(db);
     let impl_block = def_id.impl_block(db);
+    let generics = db.generics(def_id);
     let type_ref = variant_data.get_field_type_ref(&field)?;
-    Some(Ty::from_hir(db, &module, impl_block.as_ref(), &type_ref))
+    Some(Ty::from_hir(
+        db,
+        &module,
+        impl_block.as_ref(),
+        &generics,
+        &type_ref,
+    ))
 }
 
 /// The result of type inference: A mapping from expressions and patterns to types.
@@ -684,8 +784,18 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         self.type_of_pat.insert(pat, ty);
     }
 
-    fn make_ty(&self, type_ref: &TypeRef) -> Ty {
-        Ty::from_hir(self.db, &self.module, self.impl_block.as_ref(), type_ref)
+    fn make_ty(&mut self, type_ref: &TypeRef) -> Ty {
+        // TODO provide generics of function
+        let generics = Generics::default();
+        let ty = Ty::from_hir(
+            self.db,
+            &self.module,
+            self.impl_block.as_ref(),
+            &generics,
+            type_ref,
+        );
+        let ty = self.insert_type_vars(ty);
+        ty
     }
 
     fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
@@ -848,7 +958,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         Some(ty)
     }
 
-    fn resolve_variant(&self, path: Option<&Path>) -> (Ty, Option<DefId>) {
+    fn resolve_variant(&mut self, path: Option<&Path>) -> (Ty, Option<DefId>) {
         let path = if let Some(path) = path {
             path
         } else {
@@ -862,10 +972,12 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         match def_id.resolve(self.db) {
             Def::Struct(s) => {
                 let ty = type_for_struct(self.db, s);
+                let ty = self.insert_type_vars(ty);
                 (ty, Some(def_id))
             }
             Def::EnumVariant(ev) => {
                 let ty = type_for_enum_variant(self.db, ev);
+                let ty = self.insert_type_vars(ty);
                 (ty, Some(def_id))
             }
             _ => (Ty::Unknown, None),
@@ -1155,11 +1267,13 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 spread,
             } => {
                 let (ty, def_id) = self.resolve_variant(path.as_ref());
+                let substs = ty.substs().expect("adt should have substs");
                 for field in fields {
                     let field_ty = if let Some(def_id) = def_id {
                         self.db
                             .type_for_field(def_id, field.name.clone())
                             .unwrap_or(Ty::Unknown)
+                            .subst(&substs)
                     } else {
                         Ty::Unknown
                     };
@@ -1180,7 +1294,12 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             let i = name.to_string().parse::<usize>().ok();
                             i.and_then(|i| fields.get(i).cloned())
                         }
-                        Ty::Adt { def_id, .. } => self.db.type_for_field(def_id, name.clone()),
+                        Ty::Adt {
+                            def_id, ref substs, ..
+                        } => self
+                            .db
+                            .type_for_field(def_id, name.clone())
+                            .map(|ty| ty.subst(substs)),
                         _ => None,
                     })
                     .unwrap_or(Ty::Unknown);
@@ -1193,7 +1312,6 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             Expr::Cast { expr, type_ref } => {
                 let _inner_ty = self.infer_expr(*expr, &Expectation::none());
                 let cast_ty = self.make_ty(type_ref);
-                let cast_ty = self.insert_type_vars(cast_ty);
                 // TODO check the cast...
                 cast_ty
             }
@@ -1305,12 +1423,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     type_ref,
                     initializer,
                 } => {
-                    let decl_ty = Ty::from_hir_opt(
-                        self.db,
-                        &self.module,
-                        self.impl_block.as_ref(),
-                        type_ref.as_ref(),
-                    );
+                    let decl_ty = type_ref
+                        .as_ref()
+                        .map(|tr| self.make_ty(tr))
+                        .unwrap_or(Ty::Unknown);
                     let decl_ty = self.insert_type_vars(decl_ty);
                     let ty = if let Some(expr) = initializer {
                         let expr_ty = self.infer_expr(*expr, &Expectation::has_type(decl_ty));
@@ -1338,13 +1454,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
         for (type_ref, pat) in signature.params().iter().zip(body.params()) {
             let ty = self.make_ty(type_ref);
-            let ty = self.insert_type_vars(ty);
 
             self.infer_pat(*pat, &ty);
         }
         self.return_ty = {
             let ty = self.make_ty(signature.ret_type());
-            let ty = self.insert_type_vars(ty);
             ty
         };
     }
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index b221bd142..53b6d15a8 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -8,7 +8,11 @@ use rustc_hash::FxHashMap;
 
 use ra_db::SourceRootId;
 
-use crate::{HirDatabase, DefId, module_tree::ModuleId, Module, Crate, Name, Function, impl_block::{ImplId, ImplBlock, ImplItem}};
+use crate::{
+    HirDatabase, DefId, module_tree::ModuleId, Module, Crate, Name, Function,
+    impl_block::{ImplId, ImplBlock, ImplItem},
+    generics::Generics
+};
 use super::Ty;
 
 /// This is used as a key for indexing impls.
@@ -64,8 +68,15 @@ impl CrateImplBlocks {
             if let Some(_target_trait) = impl_data.target_trait() {
                 // ignore for now
             } else {
-                let target_ty =
-                    Ty::from_hir(db, &module, Some(&impl_block), impl_data.target_type());
+                // TODO provide generics of impl
+                let generics = Generics::default();
+                let target_ty = Ty::from_hir(
+                    db,
+                    &module,
+                    Some(&impl_block),
+                    &generics,
+                    impl_data.target_type(),
+                );
                 if let Some(target_ty_fp) = TyFingerprint::for_impl(&target_ty) {
                     self.impls
                         .entry(target_ty_fp)
diff --git a/crates/ra_hir/src/ty/tests/data/function_generics.txt b/crates/ra_hir/src/ty/tests/data/function_generics.txt
index 179e136a0..e44d26cfd 100644
--- a/crates/ra_hir/src/ty/tests/data/function_generics.txt
+++ b/crates/ra_hir/src/ty/tests/data/function_generics.txt
@@ -2,13 +2,13 @@
 [21; 26) '{ t }': [unknown]
 [23; 24) 't': [unknown]
 [38; 98) '{     ...(1); }': ()
-[44; 46) 'id': fn([unknown]) -> [unknown]
-[44; 52) 'id(1u32)': [unknown]
-[47; 51) '1u32': [unknown]
-[58; 68) 'id::<i128>': fn([unknown]) -> [unknown]
-[58; 71) 'id::<i128>(1)': [unknown]
-[69; 70) '1': [unknown]
-[81; 82) 'x': u64
-[90; 92) 'id': fn([unknown]) -> u64
-[90; 95) 'id(1)': u64
-[93; 94) '1': [unknown]
+[44; 46) 'id': fn(T) -> T
+[44; 52) 'id(1u32)': T
+[47; 51) '1u32': u32
+[58; 68) 'id::<i128>': fn(T) -> T
+[58; 71) 'id::<i128>(1)': T
+[69; 70) '1': T
+[81; 82) 'x': T
+[90; 92) 'id': fn(T) -> T
+[90; 95) 'id(1)': T
+[93; 94) '1': T
diff --git a/crates/ra_hir/src/ty/tests/data/generic_chain.txt b/crates/ra_hir/src/ty/tests/data/generic_chain.txt
index 720609153..568e00846 100644
--- a/crates/ra_hir/src/ty/tests/data/generic_chain.txt
+++ b/crates/ra_hir/src/ty/tests/data/generic_chain.txt
@@ -1,29 +1,29 @@
-[53; 57) 'self': A
+[53; 57) 'self': A<[unknown]>
 [65; 87) '{     ...     }': [unknown]
-[75; 79) 'self': A
+[75; 79) 'self': A<[unknown]>
 [75; 81) 'self.x': [unknown]
 [99; 100) 't': [unknown]
 [110; 115) '{ t }': [unknown]
 [112; 113) 't': [unknown]
 [135; 261) '{     ....x() }': i128
-[146; 147) 'x': [unknown]
-[150; 151) '1': [unknown]
-[162; 163) 'y': [unknown]
-[166; 168) 'id': fn([unknown]) -> [unknown]
-[166; 171) 'id(x)': [unknown]
-[169; 170) 'x': [unknown]
-[182; 183) 'a': A
-[186; 200) 'A { x: id(y) }': A
-[193; 195) 'id': fn([unknown]) -> [unknown]
-[193; 198) 'id(y)': [unknown]
-[196; 197) 'y': [unknown]
-[211; 212) 'z': [unknown]
-[215; 217) 'id': fn([unknown]) -> [unknown]
-[215; 222) 'id(a.x)': [unknown]
-[218; 219) 'a': A
-[218; 221) 'a.x': [unknown]
-[233; 234) 'b': A
-[237; 247) 'A { x: z }': A
-[244; 245) 'z': [unknown]
-[254; 255) 'b': A
+[146; 147) 'x': T
+[150; 151) '1': T
+[162; 163) 'y': T
+[166; 168) 'id': fn(T) -> T
+[166; 171) 'id(x)': T
+[169; 170) 'x': T
+[182; 183) 'a': A<T>
+[186; 200) 'A { x: id(y) }': A<T>
+[193; 195) 'id': fn(T) -> T
+[193; 198) 'id(y)': T
+[196; 197) 'y': T
+[211; 212) 'z': T
+[215; 217) 'id': fn(T) -> T
+[215; 222) 'id(a.x)': T
+[218; 219) 'a': A<T>
+[218; 221) 'a.x': T
+[233; 234) 'b': A<T>
+[237; 247) 'A { x: z }': A<T>
+[244; 245) 'z': T
+[254; 255) 'b': A<T>
 [254; 259) 'b.x()': i128
diff --git a/crates/ra_hir/src/ty/tests/data/struct_generics.txt b/crates/ra_hir/src/ty/tests/data/struct_generics.txt
index d1026b459..88cd2b409 100644
--- a/crates/ra_hir/src/ty/tests/data/struct_generics.txt
+++ b/crates/ra_hir/src/ty/tests/data/struct_generics.txt
@@ -1,15 +1,15 @@
-[36; 38) 'a1': A
+[36; 38) 'a1': A<[unknown]>
 [48; 49) 'i': i32
 [56; 147) '{     ...3.x; }': ()
-[62; 64) 'a1': A
+[62; 64) 'a1': A<[unknown]>
 [62; 66) 'a1.x': [unknown]
-[76; 78) 'a2': A
-[81; 91) 'A { x: i }': A
+[76; 78) 'a2': A<i32>
+[81; 91) 'A { x: i }': A<i32>
 [88; 89) 'i': i32
-[97; 99) 'a2': A
-[97; 101) 'a2.x': [unknown]
-[111; 113) 'a3': A
-[116; 134) 'A::<i1...x: 1 }': A
-[131; 132) '1': [unknown]
-[140; 142) 'a3': A
-[140; 144) 'a3.x': [unknown]
+[97; 99) 'a2': A<i32>
+[97; 101) 'a2.x': i32
+[111; 113) 'a3': A<i32>
+[116; 134) 'A::<i1...x: 1 }': A<i32>
+[131; 132) '1': i32
+[140; 142) 'a3': A<i32>
+[140; 144) 'a3.x': i32
diff --git a/crates/ra_ide_api/src/completion/complete_dot.rs b/crates/ra_ide_api/src/completion/complete_dot.rs
index 473edc50e..76c2f8173 100644
--- a/crates/ra_ide_api/src/completion/complete_dot.rs
+++ b/crates/ra_ide_api/src/completion/complete_dot.rs
@@ -24,7 +24,9 @@ pub(super) fn complete_dot(acc: &mut Completions, ctx: &CompletionContext) {
 fn complete_fields(acc: &mut Completions, ctx: &CompletionContext, receiver: Ty) {
     for receiver in receiver.autoderef(ctx.db) {
         match receiver {
-            Ty::Adt { def_id, .. } => {
+            Ty::Adt {
+                def_id, ref substs, ..
+            } => {
                 match def_id.resolve(ctx.db) {
                     Def::Struct(s) => {
                         for field in s.fields(ctx.db) {
@@ -33,7 +35,7 @@ fn complete_fields(acc: &mut Completions, ctx: &CompletionContext, receiver: Ty)
                                 field.name().to_string(),
                             )
                             .kind(CompletionItemKind::Field)
-                            .set_detail(field.ty(ctx.db).map(|ty| ty.to_string()))
+                            .set_detail(field.ty(ctx.db).map(|ty| ty.subst(substs).to_string()))
                             .add_to(acc);
                         }
                     }
diff --git a/crates/ra_ide_api/src/db.rs b/crates/ra_ide_api/src/db.rs
index c2978f909..d53919973 100644
--- a/crates/ra_ide_api/src/db.rs
+++ b/crates/ra_ide_api/src/db.rs
@@ -129,6 +129,7 @@ salsa::database_storage! {
             fn body_hir() for hir::db::BodyHirQuery;
             fn body_syntax_mapping() for hir::db::BodySyntaxMappingQuery;
             fn fn_signature() for hir::db::FnSignatureQuery;
+            fn generics() for hir::db::GenericsQuery;
         }
     }
 }