When suggesting assoc function with type params, include turbofish

Author: estebank

src/librustc_typeck/check/method/suggest.rs

@@ -462,15 +462,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
                 if static_sources.len() == 1 {
                     if let SelfSource::MethodCall(expr) = source {
-                        err.span_suggestion(expr.span.to(span),
-                                            "use associated function syntax instead",
-                                            format!("{}::{}",
-                                                    self.ty_to_string(actual),
-                                                    item_name),
-                                            Applicability::MachineApplicable);
+                        err.span_suggestion(
+                            expr.span.to(span),
+                            "use associated function syntax instead",
+                            format!("{}::{}", self.ty_to_value_string(actual), item_name),
+                            Applicability::MachineApplicable,
+                        );
                     } else {
-                        err.help(&format!("try with `{}::{}`",
-                                          self.ty_to_string(actual), item_name));
+                        err.help(&format!(
+                            "try with `{}::{}`",
+                            self.ty_to_value_string(actual),
+                            item_name,
+                        ));
                     }
 
                     report_candidates(span, &mut err, static_sources);
@@ -579,6 +582,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         None
     }
 
+    /// Print out the type for use in value namespace.
+    fn ty_to_value_string(&self, ty: Ty<'tcx>) -> String {
+        match ty.kind {
+            ty::Adt(def, substs) => format!("{}", ty::Instance::new(def.did, substs)),
+            _ => self.ty_to_string(ty),
+        }
+    }
+
     fn suggest_use_candidates(&self,
                               err: &mut DiagnosticBuilder<'_>,
                               mut msg: String,

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.rs

@@ -0,0 +1,11 @@
+struct GenericAssocMethod<T>(T);
+
+impl<T> GenericAssocMethod<T> {
+    fn default_hello() {}
+}
+
+fn main() {
+    let x = GenericAssocMethod(33i32);
+    x.default_hello();
+    //~^ ERROR no method named `default_hello` found for type `GenericAssocMethod<i32>`
+}

src/test/ui/suggestions/suggest-assoc-fn-call-with-turbofish.stderr

@@ -0,0 +1,22 @@
+error[E0599]: no method named `default_hello` found for type `GenericAssocMethod<i32>` in the current scope
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:9:7
+   |
+LL | struct GenericAssocMethod<T>(T);
+   | -------------------------------- method `default_hello` not found for this
+...
+LL |     x.default_hello();
+   |     --^^^^^^^^^^^^^
+   |     | |
+   |     | this is an associated function, not a method
+   |     help: use associated function syntax instead: `GenericAssocMethod::<i32>::default_hello`
+   |
+   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
+note: the candidate is defined in an impl for the type `GenericAssocMethod<_>`
+  --> $DIR/suggest-assoc-fn-call-with-turbofish.rs:4:5
+   |
+LL |     fn default_hello() {}
+   |     ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.