2 files changed, 47 insertions, 2 deletions

diff --git a/crates/ra_hir/src/source_binder.rs b/crates/ra_hir/src/source_binder.rs
index c2c6921cb..e86716d74 100644
--- a/crates/ra_hir/src/source_binder.rs
+++ b/crates/ra_hir/src/source_binder.rs
@@ -18,14 +18,18 @@ use ra_syntax::{
 use rustc_hash::{FxHashMap, FxHashSet};
 
 use crate::{
-    expr,
     expr::{
+        self,
         scope::{ExprScopes, ScopeId},
         BodySourceMap,
     },
     ids::LocationCtx,
+    name,
+    path::{PathKind, PathSegment},
+    ty::method_resolution::implements_trait,
     AsName, AstId, Const, Crate, DefWithBody, Either, Enum, Function, HirDatabase, HirFileId,
-    MacroDef, Module, Name, Path, PerNs, Resolver, Static, Struct, Trait, Ty,
+    MacroDef, Module, ModuleDef, Name, Path, PerNs, Resolution, Resolver, Static, Struct, Trait,
+    Ty,
 };
 
 /// Locates the module by `FileId`. Picks topmost module in the file.
@@ -409,6 +413,33 @@ impl SourceAnalyzer {
         crate::ty::autoderef(db, &self.resolver, canonical).map(|canonical| canonical.value)
     }
 
+    /// Checks that particular type `ty` implements `std::future::Future`.
+    /// This function is used in `.await` syntax completion.
+    pub fn impls_future(&self, db: &impl HirDatabase, ty: Ty) -> bool {
+        let std_future_path = Path {
+            kind: PathKind::Abs,
+            segments: vec![
+                PathSegment { name: name::STD, args_and_bindings: None },
+                PathSegment { name: name::FUTURE_MOD, args_and_bindings: None },
+                PathSegment { name: name::FUTURE_TYPE, args_and_bindings: None },
+            ],
+        };
+
+        let std_future_trait =
+            match self.resolver.resolve_path_segments(db, &std_future_path).into_fully_resolved() {
+                PerNs { types: Some(Resolution::Def(ModuleDef::Trait(trait_))), .. } => trait_,
+                _ => return false,
+            };
+
+        let krate = match self.resolver.krate() {
+            Some(krate) => krate,
+            _ => return false,
+        };
+
+        let canonical_ty = crate::ty::Canonical { value: ty, num_vars: 0 };
+        implements_trait(&canonical_ty, db, &self.resolver, krate, std_future_trait)
+    }
+
     #[cfg(test)]
     pub(crate) fn body_source_map(&self) -> Arc<BodySourceMap> {
         self.body_source_map.clone().unwrap()
diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
index d421bf9ef..88d012a74 100644
--- a/crates/ra_hir/src/ty/method_resolution.rs
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -255,6 +255,20 @@ fn iterate_inherent_methods<T>(
     None
 }
 
+pub(crate) fn implements_trait(
+    ty: &Canonical<Ty>,
+    db: &impl HirDatabase,
+    resolver: &Resolver,
+    krate: Crate,
+    trait_: Trait,
+) -> bool {
+    let env = lower::trait_env(db, resolver);
+    let goal = generic_implements_goal(db, env.clone(), trait_, ty.clone());
+    let solution = db.trait_solve(krate, goal);
+
+    solution.is_some()
+}
+
 impl Ty {
     // This would be nicer if it just returned an iterator, but that runs into
     // lifetime problems, because we need to borrow temp `CrateImplBlocks`.