6 files changed, 50 insertions, 11 deletions

diff --git a/crates/ra_hir/src/expr.rs b/crates/ra_hir/src/expr.rs
index 4e73590d0..e9db8282f 100644
--- a/crates/ra_hir/src/expr.rs
+++ b/crates/ra_hir/src/expr.rs
@@ -14,7 +14,7 @@ use crate::{
     name::AsName,
     type_ref::{Mutability, TypeRef},
 };
-use crate::ty::primitive::{UintTy, UncertainIntTy, UncertainFloatTy};
+use crate::{ path::GenericArgs, ty::primitive::{UintTy, UncertainIntTy, UncertainFloatTy}};
 
 pub use self::scope::{ExprScopes, ScopesWithSyntaxMapping, ScopeEntryWithSyntax};
 
@@ -193,6 +193,7 @@ pub enum Expr {
         receiver: ExprId,
         method_name: Name,
         args: Vec<ExprId>,
+        generic_args: Option<GenericArgs>,
     },
     Match {
         expr: ExprId,
@@ -597,7 +598,11 @@ impl ExprCollector {
                     Vec::new()
                 };
                 let method_name = e.name_ref().map(|nr| nr.as_name()).unwrap_or_else(Name::missing);
-                self.alloc_expr(Expr::MethodCall { receiver, method_name, args }, syntax_ptr)
+                let generic_args = e.type_arg_list().and_then(GenericArgs::from_ast);
+                self.alloc_expr(
+                    Expr::MethodCall { receiver, method_name, args, generic_args },
+                    syntax_ptr,
+                )
             }
             ast::ExprKind::MatchExpr(e) => {
                 let expr = self.collect_expr_opt(e.expr());
diff --git a/crates/ra_hir/src/path.rs b/crates/ra_hir/src/path.rs
index 8ed54607a..83bbbb741 100644
--- a/crates/ra_hir/src/path.rs
+++ b/crates/ra_hir/src/path.rs
@@ -129,7 +129,7 @@ impl Path {
 }
 
 impl GenericArgs {
-    fn from_ast(node: &ast::TypeArgList) -> Option<GenericArgs> {
+    pub 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());
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index db0a20514..f32c77faf 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -165,6 +165,17 @@ impl Substs {
     pub fn empty() -> Substs {
         Substs(Arc::new([]))
     }
+
+    /// Replaces the end of the substitutions by other ones.
+    pub(crate) fn replace_tail(self, replace_by: Vec<Ty>) -> Substs {
+        // again missing Arc::make_mut_slice...
+        let len = replace_by.len().min(self.0.len());
+        let parent_len = self.0.len() - len;
+        let mut result = Vec::with_capacity(parent_len + len);
+        result.extend(self.0.iter().take(parent_len).cloned());
+        result.extend(replace_by);
+        Substs(result.into())
+    }
 }
 
 /// A type. This is based on the `TyKind` enum in rustc (librustc/ty/sty.rs).
@@ -1367,15 +1378,34 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 }
                 ret_ty
             }
-            Expr::MethodCall { receiver, args, method_name } => {
+            Expr::MethodCall { receiver, args, method_name, generic_args } => {
                 let receiver_ty = self.infer_expr(*receiver, &Expectation::none());
                 let resolved = receiver_ty.clone().lookup_method(self.db, method_name);
-                let method_ty = match resolved {
+                let (method_ty, def_generics) = match resolved {
                     Some(func) => {
                         self.write_method_resolution(tgt_expr, func);
-                        self.db.type_for_def(func.into())
+                        (self.db.type_for_def(func.into()), Some(func.generic_params(self.db)))
+                    }
+                    None => (Ty::Unknown, None),
+                };
+                // handle provided type arguments
+                let method_ty = if let Some(generic_args) = generic_args {
+                    // if args are provided, it should be all of them, but we can't rely on that
+                    let param_count = def_generics.map(|g| g.params.len()).unwrap_or(0);
+                    let mut new_substs = Vec::with_capacity(generic_args.args.len());
+                    for arg in generic_args.args.iter().take(param_count) {
+                        match arg {
+                            GenericArg::Type(type_ref) => {
+                                let ty = self.make_ty(type_ref);
+                                new_substs.push(ty);
+                            }
+                        }
                     }
-                    None => Ty::Unknown,
+                    let substs = method_ty.substs().unwrap_or_else(Substs::empty);
+                    let substs = substs.replace_tail(new_substs);
+                    method_ty.apply_substs(substs)
+                } else {
+                    method_ty
                 };
                 let method_ty = self.insert_type_vars(method_ty);
                 let (expected_receiver_ty, param_tys, ret_ty) = match &method_ty {
diff --git a/crates/ra_hir/src/ty/snapshots/tests__infer_impl_generics.snap b/crates/ra_hir/src/ty/snapshots/tests__infer_impl_generics.snap
index eabbe52fd..44f00a52e 100644
--- a/crates/ra_hir/src/ty/snapshots/tests__infer_impl_generics.snap
+++ b/crates/ra_hir/src/ty/snapshots/tests__infer_impl_generics.snap
@@ -1,5 +1,5 @@
 ---
-created: "2019-02-16T20:53:59.657979128Z"
+created: "2019-02-16T21:58:14.029368845Z"
 creator: [email protected]
 source: crates/ra_hir/src/ty/tests.rs
 expression: "&result"
@@ -34,6 +34,6 @@ expression: "&result"
 [309; 319) 'a.z(1i128)': (u64, i64, i128)
 [313; 318) '1i128': i128
 [325; 326) 'a': A<u64, i64>
-[325; 339) 'a.z::<u128>(1)': (u64, i64, i32)
-[337; 338) '1': i32
+[325; 339) 'a.z::<u128>(1)': (u64, i64, u128)
+[337; 338) '1': u128
 
diff --git a/crates/ra_syntax/src/ast/generated.rs b/crates/ra_syntax/src/ast/generated.rs
index aa9da92da..dd91b5063 100644
--- a/crates/ra_syntax/src/ast/generated.rs
+++ b/crates/ra_syntax/src/ast/generated.rs
@@ -2095,6 +2095,10 @@ impl MethodCallExpr {
     pub fn name_ref(&self) -> Option<&NameRef> {
         super::child_opt(self)
     }
+
+    pub fn type_arg_list(&self) -> Option<&TypeArgList> {
+        super::child_opt(self)
+    }
 }
 
 // Module
diff --git a/crates/ra_syntax/src/grammar.ron b/crates/ra_syntax/src/grammar.ron
index 5ec68014b..27a123681 100644
--- a/crates/ra_syntax/src/grammar.ron
+++ b/crates/ra_syntax/src/grammar.ron
@@ -431,7 +431,7 @@ Grammar(
         ),
         "MethodCallExpr": (
             traits: ["ArgListOwner"],
-            options: [ "Expr", "NameRef" ],
+            options: [ "Expr", "NameRef", "TypeArgList" ],
         ),
         "IndexExpr": (),
         "FieldExpr": (options: ["Expr", "NameRef"]),