Merge #576

576: Beginnings of generics r=matklad a=flodiebold

This implements the beginnings of the generics infrastructure; generic parameters for structs work and are correctly substituted in fields. Functions and methods aren't handled at all yet (as the tests show).

The name resolution in `ty` really needs refactoring now, I hope to do that next ;)

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

21 files changed, 805 insertions, 97 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..88eda5ed0 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::GenericParams,
     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 generic_params(&self, db: &impl HirDatabase) -> Arc<GenericParams> {
+        db.generic_params(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 generic_params(&self, db: &impl HirDatabase) -> Arc<GenericParams> {
+        db.generic_params(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 generic_params(&self, db: &impl HirDatabase) -> Arc<GenericParams> {
+        db.generic_params(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 generic_params(&self, db: &impl HirDatabase) -> Arc<GenericParams> {
+        db.generic_params(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 generic_params(&self, db: &impl HirDatabase) -> Arc<GenericParams> {
+        db.generic_params(self.def_id)
+    }
 }
diff --git a/crates/ra_hir/src/code_model_impl/module.rs b/crates/ra_hir/src/code_model_impl/module.rs
index 7215236f9..73c212de8 100644
--- a/crates/ra_hir/src/code_model_impl/module.rs
+++ b/crates/ra_hir/src/code_model_impl/module.rs
@@ -95,7 +95,7 @@ impl Module {
     }
 
     /// Finds a child module with the specified name.
-    pub fn child_impl(&self, db: &impl HirDatabase, name: &Name) -> Option<Module> {
+    pub(crate) fn child_impl(&self, db: &impl HirDatabase, name: &Name) -> Option<Module> {
         let loc = self.def_id.loc(db);
         let module_tree = db.module_tree(loc.source_root_id);
         let child_id = loc.module_id.child(&module_tree, name)?;
@@ -103,7 +103,7 @@ impl Module {
     }
 
     /// Iterates over all child modules.
-    pub fn children_impl(&self, db: &impl HirDatabase) -> impl Iterator<Item = Module> {
+    pub(crate) fn children_impl(&self, db: &impl HirDatabase) -> impl Iterator<Item = Module> {
         // FIXME this should be implementable without collecting into a vec, but
         // it's kind of hard since the iterator needs to keep a reference to the
         // module tree.
@@ -117,7 +117,7 @@ impl Module {
         children.into_iter()
     }
 
-    pub fn parent_impl(&self, db: &impl HirDatabase) -> Option<Module> {
+    pub(crate) fn parent_impl(&self, db: &impl HirDatabase) -> Option<Module> {
         let loc = self.def_id.loc(db);
         let module_tree = db.module_tree(loc.source_root_id);
         let parent_id = loc.module_id.parent(&module_tree)?;
@@ -125,13 +125,13 @@ impl Module {
     }
 
     /// Returns a `ModuleScope`: a set of items, visible in this module.
-    pub fn scope_impl(&self, db: &impl HirDatabase) -> ModuleScope {
+    pub(crate) fn scope_impl(&self, db: &impl HirDatabase) -> ModuleScope {
         let loc = self.def_id.loc(db);
         let item_map = db.item_map(loc.source_root_id);
         item_map.per_module[&loc.module_id].clone()
     }
 
-    pub fn resolve_path_impl(&self, db: &impl HirDatabase, path: &Path) -> PerNs<DefId> {
+    pub(crate) fn resolve_path_impl(&self, db: &impl HirDatabase, path: &Path) -> PerNs<DefId> {
         let mut curr_per_ns = PerNs::types(
             match path.kind {
                 PathKind::Crate => self.crate_root(db),
@@ -147,7 +147,7 @@ impl Module {
             .def_id,
         );
 
-        for name in path.segments.iter() {
+        for segment in path.segments.iter() {
             let curr = match curr_per_ns.as_ref().take_types() {
                 Some(r) => r,
                 None => {
@@ -163,15 +163,17 @@ impl Module {
             curr_per_ns = match curr.resolve(db) {
                 Def::Module(m) => {
                     let scope = m.scope(db);
-                    match scope.get(&name) {
+                    match scope.get(&segment.name) {
                         Some(r) => r.def_id,
                         None => PerNs::none(),
                     }
                 }
                 Def::Enum(e) => {
                     // enum variant
-                    let matching_variant =
-                        e.variants(db).into_iter().find(|(n, _variant)| n == name);
+                    let matching_variant = e
+                        .variants(db)
+                        .into_iter()
+                        .find(|(n, _variant)| n == &segment.name);
 
                     match matching_variant {
                         Some((_n, variant)) => PerNs::both(variant.def_id(), e.def_id()),
@@ -189,7 +191,10 @@ impl Module {
         curr_per_ns
     }
 
-    pub fn problems_impl(&self, db: &impl HirDatabase) -> Vec<(TreeArc<SyntaxNode>, Problem)> {
+    pub(crate) fn problems_impl(
+        &self,
+        db: &impl HirDatabase,
+    ) -> Vec<(TreeArc<SyntaxNode>, Problem)> {
         let loc = self.def_id.loc(db);
         let module_tree = db.module_tree(loc.source_root_id);
         loc.module_id.problems(&module_tree, db)
diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 60065cf6a..f383701d7 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::GenericParams,
 };
 
 #[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::GenericParams::generic_params_query)]
+    fn generic_params(&self, def_id: DefId) -> Arc<GenericParams>;
+
     #[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..d8248ad49
--- /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 GenericParams {
+    pub(crate) params: Vec<GenericParam>,
+}
+
+impl GenericParams {
+    pub(crate) fn generic_params_query(db: &impl HirDatabase, def_id: DefId) -> Arc<GenericParams> {
+        let (_file_id, node) = def_id.source(db);
+        let mut generics = GenericParams::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/ids.rs b/crates/ra_hir/src/ids.rs
index 0d8e67547..c5408e277 100644
--- a/crates/ra_hir/src/ids.rs
+++ b/crates/ra_hir/src/ids.rs
@@ -151,6 +151,15 @@ pub(crate) enum DefKind {
     Type,
     Item,
 
+    /// The constructor of a struct. E.g. if we have `struct Foo(usize)`, the
+    /// name `Foo` needs to resolve to different types depending on whether we
+    /// are in the types or values namespace: As a type, `Foo` of course refers
+    /// to the struct `Foo`; as a value, `Foo` is a callable type with signature
+    /// `(usize) -> Foo`. The cleanest approach to handle this seems to be to
+    /// have different defs in the two namespaces.
+    ///
+    /// rustc does the same; note that it even creates a struct constructor if
+    /// the struct isn't a tuple struct (see `CtorKind::Fictive` in rustc).
     StructCtor,
 }
 
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..6e6f2f04b 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 generic_params() for db::GenericParamsQuery;
         }
     }
 }
diff --git a/crates/ra_hir/src/nameres.rs b/crates/ra_hir/src/nameres.rs
index 4efafd409..4874e82f3 100644
--- a/crates/ra_hir/src/nameres.rs
+++ b/crates/ra_hir/src/nameres.rs
@@ -221,10 +221,10 @@ where
             };
         }
         for (import_id, import_data) in input.imports.iter() {
-            if let Some(name) = import_data.path.segments.iter().last() {
+            if let Some(segment) = import_data.path.segments.iter().last() {
                 if !import_data.is_glob {
                     module_items.items.insert(
-                        name.clone(),
+                        segment.name.clone(),
                         Resolution {
                             def_id: PerNs::none(),
                             import: Some(import_id),
@@ -319,13 +319,13 @@ where
             PathKind::Crate => module_id.crate_root(&self.module_tree),
         };
 
-        for (i, name) in import.path.segments.iter().enumerate() {
+        for (i, segment) in import.path.segments.iter().enumerate() {
             let is_last = i == import.path.segments.len() - 1;
 
-            let def_id = match self.result.per_module[&curr].items.get(name) {
+            let def_id = match self.result.per_module[&curr].items.get(&segment.name) {
                 Some(res) if !res.def_id.is_none() => res.def_id,
                 _ => {
-                    log::debug!("path segment {:?} not found", name);
+                    log::debug!("path segment {:?} not found", segment.name);
                     return false;
                 }
             };
@@ -336,7 +336,7 @@ where
                 } else {
                     log::debug!(
                         "path segment {:?} resolved to value only, but is not last",
-                        name
+                        segment.name
                     );
                     return false;
                 };
@@ -358,17 +358,17 @@ where
                             log::debug!("resolving {:?} in other source root", path);
                             let def_id = module.resolve_path(self.db, &path);
                             if !def_id.is_none() {
-                                let name = path.segments.last().unwrap();
+                                let last_segment = path.segments.last().unwrap();
                                 self.update(module_id, |items| {
                                     let res = Resolution {
                                         def_id,
                                         import: Some(import_id),
                                     };
-                                    items.items.insert(name.clone(), res);
+                                    items.items.insert(last_segment.name.clone(), res);
                                 });
                                 log::debug!(
                                     "resolved import {:?} ({:?}) cross-source root to {:?}",
-                                    name,
+                                    last_segment.name,
                                     import,
                                     def_id.map(|did| did.loc(self.db))
                                 );
@@ -382,7 +382,7 @@ where
                     _ => {
                         log::debug!(
                             "path segment {:?} resolved to non-module {:?}, but is not last",
-                            name,
+                            segment.name,
                             type_def_id.loc(self.db)
                         );
                         return true; // this resolved to a non-module, so the path won't ever resolve
@@ -391,7 +391,7 @@ where
             } else {
                 log::debug!(
                     "resolved import {:?} ({:?}) within source root to {:?}",
-                    name,
+                    segment.name,
                     import,
                     def_id.map(|did| did.loc(self.db))
                 );
@@ -400,7 +400,7 @@ where
                         def_id,
                         import: Some(import_id),
                     };
-                    items.items.insert(name.clone(), res);
+                    items.items.insert(segment.name.clone(), res);
                 })
             }
         }
diff --git a/crates/ra_hir/src/path.rs b/crates/ra_hir/src/path.rs
index 7b0ce3b61..c3d14c689 100644
--- a/crates/ra_hir/src/path.rs
+++ b/crates/ra_hir/src/path.rs
@@ -1,11 +1,35 @@
+use std::sync::Arc;
+
 use ra_syntax::{ast, AstNode};
 
-use crate::{Name, AsName};
+use crate::{Name, AsName, type_ref::TypeRef};
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct Path {
     pub kind: PathKind,
-    pub segments: Vec<Name>,
+    pub segments: Vec<PathSegment>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct PathSegment {
+    pub name: Name,
+    pub args_and_bindings: Option<Arc<GenericArgs>>,
+}
+
+/// Generic arguments to a path segment (e.g. the `i32` in `Option<i32>`). This
+/// can (in the future) also include bindings of associated types, like in
+/// `Iterator<Item = Foo>`.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct GenericArgs {
+    pub args: Vec<GenericArg>,
+    // someday also bindings
+}
+
+/// A single generic argument.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum GenericArg {
+    Type(TypeRef),
+    // or lifetime...
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -34,7 +58,17 @@ impl Path {
         loop {
             let segment = path.segment()?;
             match segment.kind()? {
-                ast::PathSegmentKind::Name(name) => segments.push(name.as_name()),
+                ast::PathSegmentKind::Name(name) => {
+                    let args = segment
+                        .type_arg_list()
+                        .and_then(GenericArgs::from_ast)
+                        .map(Arc::new);
+                    let segment = PathSegment {
+                        name: name.as_name(),
+                        args_and_bindings: args,
+                    };
+                    segments.push(segment);
+                }
                 ast::PathSegmentKind::CrateKw => {
                     kind = PathKind::Crate;
                     break;
@@ -88,7 +122,23 @@ impl Path {
         if self.kind != PathKind::Plain || self.segments.len() > 1 {
             return None;
         }
-        self.segments.first()
+        self.segments.first().map(|s| &s.name)
+    }
+}
+
+impl GenericArgs {
+    fn from_ast(node: &ast::TypeArgList) -> Option<GenericArgs> {
+        let mut args = Vec::new();
+        for type_arg in node.type_args() {
+            let type_ref = TypeRef::from_ast_opt(type_arg.type_ref());
+            args.push(GenericArg::Type(type_ref));
+        }
+        // lifetimes and assoc type args ignored for now
+        if args.len() > 0 {
+            Some(GenericArgs { args })
+        } else {
+            None
+        }
     }
 }
 
@@ -96,7 +146,10 @@ impl From<Name> for Path {
     fn from(name: Name) -> Path {
         Path {
             kind: PathKind::Plain,
-            segments: vec![name],
+            segments: vec![PathSegment {
+                name,
+                args_and_bindings: None,
+            }],
         }
     }
 }
@@ -160,7 +213,10 @@ fn convert_path(prefix: Option<Path>, path: &ast::Path) -> Option<Path> {
                 kind: PathKind::Plain,
                 segments: Vec::with_capacity(1),
             });
-            res.segments.push(name.as_name());
+            res.segments.push(PathSegment {
+                name: name.as_name(),
+                args_and_bindings: None, // no type args in use
+            });
             res
         }
         ast::PathSegmentKind::CrateKw => {
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index 8d6493887..9b7182485 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -37,6 +37,8 @@ use crate::{
     type_ref::{TypeRef, Mutability},
     name::KnownName,
     expr::{Body, Expr, BindingAnnotation, Literal, ExprId, Pat, PatId, UnaryOp, BinaryOp, Statement, FieldPat},
+    generics::GenericParams,
+    path::GenericArg,
 };
 
 /// The ID of a type variable.
@@ -151,10 +153,20 @@ impl Expectation {
     }
 }
 
+/// A list of substitutions for generic parameters.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct Substs(Arc<[Ty]>);
+
+impl Substs {
+    pub fn empty() -> Substs {
+        Substs(Arc::new([]))
+    }
+}
+
 /// 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 +187,8 @@ 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 +247,15 @@ 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 (starting with parameters from the
+        /// surrounding impl, then the current function).
+        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 +269,7 @@ 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,
@@ -259,8 +278,12 @@ pub struct FnSig {
 impl Ty {
     pub(crate) fn from_hir(
         db: &impl HirDatabase,
+        // TODO: the next three parameters basically describe the scope for name
+        // resolution; this should be refactored into something like a general
+        // resolver architecture
         module: &Module,
         impl_block: Option<&ImplBlock>,
+        generics: &GenericParams,
         type_ref: &TypeRef,
     ) -> Self {
         match type_ref {
@@ -268,32 +291,32 @@ 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 +335,19 @@ impl Ty {
         db: &impl HirDatabase,
         module: &Module,
         impl_block: Option<&ImplBlock>,
+        generics: &GenericParams,
         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: &GenericParams,
         path: &Path,
     ) -> Self {
         if let Some(name) = path.as_ident() {
@@ -329,7 +356,15 @@ 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 = &GenericParams::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,
@@ -337,16 +372,89 @@ 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(),
+                };
             }
         }
 
         // Resolve in module (in type namespace)
-        let resolved = if let Some(r) = module.resolve_path(db, path).take_types() {
-            r
-        } else {
-            return Ty::Unknown;
+        let resolved = match module.resolve_path(db, path).take_types() {
+            Some(r) => r,
+            None => return Ty::Unknown,
         };
-        db.type_for_def(resolved)
+        let ty = db.type_for_def(resolved);
+        let substs = Ty::substs_from_path(db, module, impl_block, generics, path, resolved);
+        ty.apply_substs(substs)
+    }
+
+    /// Collect generic arguments from a path into a `Substs`. See also
+    /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
+    fn substs_from_path(
+        db: &impl HirDatabase,
+        // the scope of the segment...
+        module: &Module,
+        impl_block: Option<&ImplBlock>,
+        outer_generics: &GenericParams,
+        path: &Path,
+        resolved: DefId,
+    ) -> Substs {
+        let mut substs = Vec::new();
+        let def = resolved.resolve(db);
+        let last = path
+            .segments
+            .last()
+            .expect("path should have at least one segment");
+        let (def_generics, segment) = match def {
+            Def::Struct(s) => (s.generic_params(db), last),
+            Def::Enum(e) => (e.generic_params(db), last),
+            Def::Function(f) => (f.generic_params(db), last),
+            Def::Trait(t) => (t.generic_params(db), last),
+            Def::EnumVariant(ev) => {
+                // the generic args for an enum variant may be either specified
+                // on the segment referring to the enum, or on the segment
+                // referring to the variant. So `Option::<T>::None` and
+                // `Option::None::<T>` are both allowed (though the former is
+                // preferred). See also `def_ids_for_path_segments` in rustc.
+                let len = path.segments.len();
+                let segment = if len >= 2 && path.segments[len - 2].args_and_bindings.is_some() {
+                    // Option::<T>::None
+                    &path.segments[len - 2]
+                } else {
+                    // Option::None::<T>
+                    last
+                };
+                (ev.parent_enum(db).generic_params(db), segment)
+            }
+            _ => return Substs::empty(),
+        };
+        // substs_from_path
+        if let Some(generic_args) = &segment.args_and_bindings {
+            // if args are provided, it should be all of them, but we can't rely on that
+            let param_count = def_generics.params.len();
+            for arg in generic_args.args.iter().take(param_count) {
+                match arg {
+                    GenericArg::Type(type_ref) => {
+                        let ty = Ty::from_hir(db, module, impl_block, outer_generics, type_ref);
+                        substs.push(ty);
+                    }
+                }
+            }
+        }
+        // add placeholders for args that were not provided
+        // TODO: handle defaults
+        for _ in segment
+            .args_and_bindings
+            .as_ref()
+            .map(|ga| ga.args.len())
+            .unwrap_or(0)..def_generics.params.len()
+        {
+            substs.push(Ty::Unknown);
+        }
+        assert_eq!(substs.len(), def_generics.params.len());
+        Substs(substs.into())
     }
 
     pub fn unit() -> Self {
@@ -374,7 +482,14 @@ 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 +509,49 @@ impl Ty {
             _ => None,
         }
     }
+
+    /// If this is a type with type parameters (an ADT or function), replaces
+    /// the `Substs` for these type parameters with the given ones. (So e.g. if
+    /// `self` is `Option<_>` and the substs contain `u32`, we'll have
+    /// `Option<u32>` afterwards.)
+    pub fn apply_substs(self, substs: Substs) -> Ty {
+        match self {
+            Ty::Adt { def_id, name, .. } => Ty::Adt {
+                def_id,
+                name,
+                substs,
+            },
+            _ => self,
+        }
+    }
+
+    /// 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: does this indicate a bug? i.e. should we always
+                    // have substs for all type params? (they might contain the
+                    // params themselves again...)
+                    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 +583,17 @@ 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 +608,49 @@ 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.generic_params(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: &GenericParams) -> 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.generic_params(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.generic_params(db);
     Ty::Adt {
         def_id: s.def_id(),
         name: s.name(db).unwrap_or_else(Name::missing),
+        substs: make_substs(&generics),
     }
 }
 
@@ -495,9 +684,9 @@ pub(super) fn type_for_def(db: &impl HirDatabase, def_id: DefId) -> Ty {
 
 pub(super) fn type_for_field(db: &impl HirDatabase, def_id: DefId, field: Name) -> Option<Ty> {
     let def = def_id.resolve(db);
-    let variant_data = match def {
-        Def::Struct(s) => s.variant_data(db),
-        Def::EnumVariant(ev) => ev.variant_data(db),
+    let (variant_data, generics) = match def {
+        Def::Struct(s) => (s.variant_data(db), s.generic_params(db)),
+        Def::EnumVariant(ev) => (ev.variant_data(db), ev.parent_enum(db).generic_params(db)),
         // TODO: unions
         _ => panic!(
             "trying to get type for field in non-struct/variant {:?}",
@@ -507,7 +696,13 @@ 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 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 +879,26 @@ 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 = GenericParams::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_substs(&mut self, substs1: &Substs, substs2: &Substs) -> bool {
+        substs1
+            .0
+            .iter()
+            .zip(substs2.0.iter())
+            .all(|(t1, t2)| self.unify(t1, t2))
     }
 
     fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
@@ -708,12 +921,16 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             (Ty::Bool, _) | (Ty::Str, _) | (Ty::Never, _) | (Ty::Char, _) => ty1 == ty2,
             (
                 Ty::Adt {
-                    def_id: def_id1, ..
+                    def_id: def_id1,
+                    substs: substs1,
+                    ..
                 },
                 Ty::Adt {
-                    def_id: def_id2, ..
+                    def_id: def_id2,
+                    substs: substs2,
+                    ..
                 },
-            ) if def_id1 == def_id2 => true,
+            ) if def_id1 == def_id2 => self.unify_substs(substs1, substs2),
             (Ty::Slice(t1), Ty::Slice(t2)) => self.unify(t1, t2),
             (Ty::RawPtr(t1, m1), Ty::RawPtr(t2, m2)) if m1 == m2 => self.unify(t1, t2),
             (Ty::Ref(t1, m1), Ty::Ref(t2, m2)) if m1 == m2 => self.unify(t1, t2),
@@ -848,73 +1065,100 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         Some(ty)
     }
 
-    fn resolve_variant(&self, path: Option<&Path>) -> (Ty, Option<DefId>) {
-        let path = if let Some(path) = path {
-            path
-        } else {
-            return (Ty::Unknown, None);
+    fn resolve_variant(&mut self, path: Option<&Path>) -> (Ty, Option<DefId>) {
+        let path = match path {
+            Some(path) => path,
+            None => return (Ty::Unknown, None),
         };
-        let def_id = if let Some(def_id) = self.module.resolve_path(self.db, &path).take_types() {
-            def_id
-        } else {
-            return (Ty::Unknown, None);
+        let def_id = match self.module.resolve_path(self.db, &path).take_types() {
+            Some(def_id) => def_id,
+            _ => return (Ty::Unknown, None),
         };
+        // TODO remove the duplication between here and `Ty::from_path`?
+        // TODO provide generics of function
+        let generics = GenericParams::default();
+        let substs = Ty::substs_from_path(
+            self.db,
+            &self.module,
+            self.impl_block.as_ref(),
+            &generics,
+            path,
+            def_id,
+        );
         match def_id.resolve(self.db) {
             Def::Struct(s) => {
                 let ty = type_for_struct(self.db, s);
+                let ty = self.insert_type_vars(ty.apply_substs(substs));
                 (ty, Some(def_id))
             }
             Def::EnumVariant(ev) => {
                 let ty = type_for_enum_variant(self.db, ev);
+                let ty = self.insert_type_vars(ty.apply_substs(substs));
                 (ty, Some(def_id))
             }
             _ => (Ty::Unknown, None),
         }
     }
 
-    fn resolve_fields(&self, path: Option<&Path>) -> Option<(Ty, Vec<StructField>)> {
-        let def_id = self.module.resolve_path(self.db, path?).take_types()?;
+    fn resolve_fields(&mut self, path: Option<&Path>) -> Option<(Ty, Vec<StructField>)> {
+        let (ty, def_id) = self.resolve_variant(path);
+        let def_id = def_id?;
         let def = def_id.resolve(self.db);
 
         match def {
             Def::Struct(s) => {
                 let fields = s.fields(self.db);
-                Some((type_for_struct(self.db, s), fields))
+                Some((ty, fields))
             }
             Def::EnumVariant(ev) => {
                 let fields = ev.fields(self.db);
-                Some((type_for_enum_variant(self.db, ev), fields))
+                Some((ty, fields))
             }
             _ => None,
         }
     }
 
-    fn infer_tuple_struct_pat(&mut self, path: Option<&Path>, subpats: &[PatId]) -> Ty {
+    fn infer_tuple_struct_pat(
+        &mut self,
+        path: Option<&Path>,
+        subpats: &[PatId],
+        expected: &Ty,
+    ) -> Ty {
         let (ty, fields) = self
             .resolve_fields(path)
             .unwrap_or((Ty::Unknown, Vec::new()));
 
+        self.unify(&ty, expected);
+
+        let substs = ty.substs().expect("adt should have substs");
+
         for (i, &subpat) in subpats.iter().enumerate() {
             let expected_ty = fields
                 .get(i)
                 .and_then(|field| field.ty(self.db))
-                .unwrap_or(Ty::Unknown);
+                .unwrap_or(Ty::Unknown)
+                .subst(&substs);
             self.infer_pat(subpat, &expected_ty);
         }
 
         ty
     }
 
-    fn infer_struct_pat(&mut self, path: Option<&Path>, subpats: &[FieldPat]) -> Ty {
+    fn infer_struct_pat(&mut self, path: Option<&Path>, subpats: &[FieldPat], expected: &Ty) -> Ty {
         let (ty, fields) = self
             .resolve_fields(path)
             .unwrap_or((Ty::Unknown, Vec::new()));
 
+        self.unify(&ty, expected);
+
+        let substs = ty.substs().expect("adt should have substs");
+
         for subpat in subpats {
             let matching_field = fields.iter().find(|field| field.name() == &subpat.name);
             let expected_ty = matching_field
                 .and_then(|field| field.ty(self.db))
-                .unwrap_or(Ty::Unknown);
+                .unwrap_or(Ty::Unknown)
+                .subst(&substs);
             self.infer_pat(subpat.pat, &expected_ty);
         }
 
@@ -959,11 +1203,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             Pat::TupleStruct {
                 path: ref p,
                 args: ref subpats,
-            } => self.infer_tuple_struct_pat(p.as_ref(), subpats),
+            } => self.infer_tuple_struct_pat(p.as_ref(), subpats, expected),
             Pat::Struct {
                 path: ref p,
                 args: ref fields,
-            } => self.infer_struct_pat(p.as_ref(), fields),
+            } => self.infer_struct_pat(p.as_ref(), fields, expected),
             Pat::Path(path) => self
                 .module
                 .resolve_path(self.db, &path)
@@ -1155,11 +1399,13 @@ 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 +1426,12 @@ 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 +1444,6 @@ 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 +1555,10 @@ 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 +1586,11 @@ 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..9f65c5fe1 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::GenericParams
+};
 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 = GenericParams::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.rs b/crates/ra_hir/src/ty/tests.rs
index fc4054159..06e32df59 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -418,6 +418,95 @@ fn test() {
     );
 }
 
+#[test]
+fn infer_struct_generics() {
+    check_inference(
+        r#"
+struct A<T> {
+    x: T,
+}
+
+fn test(a1: A<u32>, i: i32) {
+    a1.x;
+    let a2 = A { x: i };
+    a2.x;
+    let a3 = A::<i128> { x: 1 };
+    a3.x;
+}
+"#,
+        "struct_generics.txt",
+    );
+}
+
+#[test]
+fn infer_generics_in_patterns() {
+    check_inference(
+        r#"
+struct A<T> {
+    x: T,
+}
+
+enum Option<T> {
+    Some(T),
+    None,
+}
+
+fn test(a1: A<u32>, o: Option<u64>) {
+    let A { x: x2 } = a1;
+    let A::<i64> { x: x3 } = A { x: 1 };
+    match o {
+        Option::Some(t) => t,
+        _ => 1,
+    };
+}
+"#,
+        "generics_in_patterns.txt",
+    );
+}
+
+#[test]
+fn infer_function_generics() {
+    check_inference(
+        r#"
+fn id<T>(t: T) -> T { t }
+
+fn test() {
+    id(1u32);
+    id::<i128>(1);
+    let x: u64 = id(1);
+}
+"#,
+        "function_generics.txt",
+    );
+}
+
+#[test]
+fn infer_generic_chain() {
+    check_inference(
+        r#"
+struct A<T> {
+    x: T,
+}
+impl<T2> A<T2> {
+    fn x(self) -> T2 {
+        self.x
+    }
+}
+fn id<T>(t: T) -> T { t }
+
+fn test() -> i128 {
+     let x = 1;
+     let y = id(x);
+     let a = A { x: id(y) };
+     let z = id(a.x);
+     let b = A { x: z };
+     b.x()
+}
+"#,
+        "generic_chain.txt",
+    );
+}
+
 fn infer(content: &str) -> String {
     let (db, _, file_id) = MockDatabase::with_single_file(content);
     let source_file = db.source_file(file_id);
diff --git a/crates/ra_hir/src/ty/tests/data/function_generics.txt b/crates/ra_hir/src/ty/tests/data/function_generics.txt
new file mode 100644
index 000000000..e44d26cfd
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/function_generics.txt
@@ -0,0 +1,14 @@
+[10; 11) 't': [unknown]
+[21; 26) '{ t }': [unknown]
+[23; 24) 't': [unknown]
+[38; 98) '{     ...(1); }': ()
+[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
new file mode 100644
index 000000000..568e00846
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/generic_chain.txt
@@ -0,0 +1,29 @@
+[53; 57) 'self': A<[unknown]>
+[65; 87) '{     ...     }': [unknown]
+[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': 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/generics_in_patterns.txt b/crates/ra_hir/src/ty/tests/data/generics_in_patterns.txt
new file mode 100644
index 000000000..1b01ef19e
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/generics_in_patterns.txt
@@ -0,0 +1,17 @@
+[79; 81) 'a1': A<u32>
+[91; 92) 'o': Option<u64>
+[107; 244) '{     ...  }; }': ()
+[117; 128) 'A { x: x2 }': A<u32>
+[124; 126) 'x2': u32
+[131; 133) 'a1': A<u32>
+[143; 161) 'A::<i6...: x3 }': A<i64>
+[157; 159) 'x3': i64
+[164; 174) 'A { x: 1 }': A<i64>
+[171; 172) '1': i64
+[180; 241) 'match ...     }': u64
+[186; 187) 'o': Option<u64>
+[198; 213) 'Option::Some(t)': Option<u64>
+[211; 212) 't': u64
+[217; 218) 't': u64
+[228; 229) '_': Option<u64>
+[233; 234) '1': u64
diff --git a/crates/ra_hir/src/ty/tests/data/struct_generics.txt b/crates/ra_hir/src/ty/tests/data/struct_generics.txt
new file mode 100644
index 000000000..1024a39a9
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/struct_generics.txt
@@ -0,0 +1,15 @@
+[36; 38) 'a1': A<u32>
+[48; 49) 'i': i32
+[56; 147) '{     ...3.x; }': ()
+[62; 64) 'a1': A<u32>
+[62; 66) 'a1.x': u32
+[76; 78) 'a2': A<i32>
+[81; 91) 'A { x: i }': A<i32>
+[88; 89) 'i': i32
+[97; 99) 'a2': A<i32>
+[97; 101) 'a2.x': i32
+[111; 113) 'a3': A<i128>
+[116; 134) 'A::<i1...x: 1 }': A<i128>
+[131; 132) '1': i128
+[140; 142) 'a3': A<i128>
+[140; 144) 'a3.x': i128
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..a1b666899 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 generic_params() for hir::db::GenericParamsQuery;
         }
     }
 }
diff --git a/crates/ra_syntax/src/ast/generated.rs b/crates/ra_syntax/src/ast/generated.rs
index 271040bf4..9fe946172 100644
--- a/crates/ra_syntax/src/ast/generated.rs
+++ b/crates/ra_syntax/src/ast/generated.rs
@@ -105,6 +105,38 @@ impl ArrayType {
     }
 }
 
+// AssocTypeArg
+#[derive(Debug, PartialEq, Eq, Hash)]
+#[repr(transparent)]
+pub struct AssocTypeArg {
+    pub(crate) syntax: SyntaxNode,
+}
+unsafe impl TransparentNewType for AssocTypeArg {
+    type Repr = rowan::SyntaxNode<RaTypes>;
+}
+
+impl AstNode for AssocTypeArg {
+    fn cast(syntax: &SyntaxNode) -> Option<&Self> {
+        match syntax.kind() {
+            ASSOC_TYPE_ARG => Some(AssocTypeArg::from_repr(syntax.into_repr())),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+    fn to_owned(&self) -> TreeArc<AssocTypeArg> { TreeArc::cast(self.syntax.to_owned()) }
+}
+
+
+impl AssocTypeArg {
+    pub fn name_ref(&self) -> Option<&NameRef> {
+        super::child_opt(self)
+    }
+
+    pub fn type_ref(&self) -> Option<&TypeRef> {
+        super::child_opt(self)
+    }
+}
+
 // Attr
 #[derive(Debug, PartialEq, Eq, Hash)]
 #[repr(transparent)]
@@ -1397,6 +1429,34 @@ impl AstNode for Lifetime {
 impl ast::AstToken for Lifetime {}
 impl Lifetime {}
 
+// LifetimeArg
+#[derive(Debug, PartialEq, Eq, Hash)]
+#[repr(transparent)]
+pub struct LifetimeArg {
+    pub(crate) syntax: SyntaxNode,
+}
+unsafe impl TransparentNewType for LifetimeArg {
+    type Repr = rowan::SyntaxNode<RaTypes>;
+}
+
+impl AstNode for LifetimeArg {
+    fn cast(syntax: &SyntaxNode) -> Option<&Self> {
+        match syntax.kind() {
+            LIFETIME_ARG => Some(LifetimeArg::from_repr(syntax.into_repr())),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+    fn to_owned(&self) -> TreeArc<LifetimeArg> { TreeArc::cast(self.syntax.to_owned()) }
+}
+
+
+impl LifetimeArg {
+    pub fn lifetime(&self) -> Option<&Lifetime> {
+        super::child_opt(self)
+    }
+}
+
 // LifetimeParam
 #[derive(Debug, PartialEq, Eq, Hash)]
 #[repr(transparent)]
@@ -2355,6 +2415,10 @@ impl PathSegment {
     pub fn name_ref(&self) -> Option<&NameRef> {
         super::child_opt(self)
     }
+
+    pub fn type_arg_list(&self) -> Option<&TypeArgList> {
+        super::child_opt(self)
+    }
 }
 
 // PathType
@@ -3335,6 +3399,70 @@ impl TupleType {
     }
 }
 
+// TypeArg
+#[derive(Debug, PartialEq, Eq, Hash)]
+#[repr(transparent)]
+pub struct TypeArg {
+    pub(crate) syntax: SyntaxNode,
+}
+unsafe impl TransparentNewType for TypeArg {
+    type Repr = rowan::SyntaxNode<RaTypes>;
+}
+
+impl AstNode for TypeArg {
+    fn cast(syntax: &SyntaxNode) -> Option<&Self> {
+        match syntax.kind() {
+            TYPE_ARG => Some(TypeArg::from_repr(syntax.into_repr())),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+    fn to_owned(&self) -> TreeArc<TypeArg> { TreeArc::cast(self.syntax.to_owned()) }
+}
+
+
+impl TypeArg {
+    pub fn type_ref(&self) -> Option<&TypeRef> {
+        super::child_opt(self)
+    }
+}
+
+// TypeArgList
+#[derive(Debug, PartialEq, Eq, Hash)]
+#[repr(transparent)]
+pub struct TypeArgList {
+    pub(crate) syntax: SyntaxNode,
+}
+unsafe impl TransparentNewType for TypeArgList {
+    type Repr = rowan::SyntaxNode<RaTypes>;
+}
+
+impl AstNode for TypeArgList {
+    fn cast(syntax: &SyntaxNode) -> Option<&Self> {
+        match syntax.kind() {
+            TYPE_ARG_LIST => Some(TypeArgList::from_repr(syntax.into_repr())),
+            _ => None,
+        }
+    }
+    fn syntax(&self) -> &SyntaxNode { &self.syntax }
+    fn to_owned(&self) -> TreeArc<TypeArgList> { TreeArc::cast(self.syntax.to_owned()) }
+}
+
+
+impl TypeArgList {
+    pub fn type_args(&self) -> impl Iterator<Item = &TypeArg> {
+        super::children(self)
+    }
+
+    pub fn lifetime_args(&self) -> impl Iterator<Item = &LifetimeArg> {
+        super::children(self)
+    }
+
+    pub fn assoc_type_args(&self) -> impl Iterator<Item = &AssocTypeArg> {
+        super::children(self)
+    }
+}
+
 // TypeDef
 #[derive(Debug, PartialEq, Eq, Hash)]
 #[repr(transparent)]
diff --git a/crates/ra_syntax/src/grammar.ron b/crates/ra_syntax/src/grammar.ron
index fc47c36d3..0385183fd 100644
--- a/crates/ra_syntax/src/grammar.ron
+++ b/crates/ra_syntax/src/grammar.ron
@@ -597,8 +597,16 @@ Grammar(
             ]
         ),
         "PathSegment": (
-            options: [ "NameRef" ]
+            options: [ "NameRef", "TypeArgList" ]
         ),
+        "TypeArgList": (collections: [
+            ["type_args", "TypeArg"],
+            ["lifetime_args", "LifetimeArg"],
+            ["assoc_type_args", "AssocTypeArg"],
+        ]),
+        "TypeArg": (options: ["TypeRef"]),
+        "AssocTypeArg": (options: ["NameRef", "TypeRef"]),
+        "LifetimeArg": (options: ["Lifetime"]),
         "Comment": ( traits: ["AstToken"] ),
         "Whitespace": ( traits: ["AstToken"] ),
     },