Implement completion for the .await syntax

crates/ra_hir/src/source_binder.rs

@@ -23,6 +23,7 @@ use crate::{
         scope::{ExprScopes, ScopeId},
         BodySourceMap,
     },
+    ty::method_resolution::implements_trait,
     ids::LocationCtx,
     AsName, AstId, Const, Crate, DefWithBody, Either, Enum, Function, HirDatabase, HirFileId,
     MacroDef, Module, Name, Path, PerNs, Resolver, Static, Struct, Trait, Ty,
@@ -409,6 +410,42 @@ impl SourceAnalyzer {
         crate::ty::autoderef(db, &self.resolver, canonical).map(|canonical| canonical.value)
     }
 
+    /// Checks that particular type `ty` implements `std::future::Future` trait.
+    /// This function is used in `.await` syntax completion.
+    pub fn impls_future(&self, db: &impl HirDatabase, ty: Ty) -> bool {
+        // Search for std::future::Future trait in scope
+        let future_trait = self.resolver.traits_in_scope(db)
+            .into_iter()
+            .filter(|t| {
+                let std = t.module(db).parent(db)
+                    .and_then(|m| m
+                        .name(db)
+                        .and_then(|n| Some(n.to_string() == "std")))
+                    .unwrap_or(false);
+
+                let future = t.module(db).name(db)
+                    .and_then(|n| Some(n.to_string() == "future"))
+                    .unwrap_or(false);
+
+                let future_trait = t.name(db)
+                    .and_then(|n| Some(n.to_string() == "Future"))
+                    .unwrap_or(false);
+
+                std && future && future_trait
+            })
+            .nth(0);
+
+        if let Some(trait_) = future_trait {
+            let krate = self.resolver.krate();
+            if let Some(krate) = krate {
+                let canonical_ty = crate::ty::Canonical { value: ty, num_vars: 0 };
+                return implements_trait(&canonical_ty, db, &self.resolver, krate, trait_);
+            }
+        }
+
+        false
+    }
+
     #[cfg(test)]
     pub(crate) fn body_source_map(&self) -> Arc<BodySourceMap> {
         self.body_source_map.clone().unwrap()

crates/ra_hir/src/ty/method_resolution.rs

@@ -15,7 +15,7 @@ use crate::{
     resolve::Resolver,
     traits::TraitItem,
     ty::primitive::{FloatBitness, UncertainFloatTy, UncertainIntTy},
-    ty::{Ty, TypeCtor},
+    ty::{Ty, TypeCtor, traits::Solution},
     Crate, Function, HirDatabase, Module, Name, Trait,
 };
 
@@ -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);
+
+    if let Some(solution) = solution {
+        if let Solution::Unique(_) = solution {
+            return true
+        }
+    }
+
+    false
+}
+
 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`.