Add clarification on E0308 about opaque types

diff --git a/src/librustc/ty/error.rs b/src/librustc/ty/error.rs
index 6daecd7ae941aca89851207c958000cea1e7959d..c1593799286efd1f91ab2bd4a0e655081cebc142 100644 (file)
--- a/src/librustc/ty/error.rs
+++ b/src/librustc/ty/error.rs
@@ -268,6 +268,7 @@ pub fn note_and_explain_type_err(
                     let e_str = values.expected.to_string();
                     let f_str = values.found.to_string();
                     if &e_str == &f_str && &e_str == "impl std::future::Future" {
+                        // FIXME: use non-string based check.
                         db.help("if both futures resolve to the same type, consider `await`ing \
                                  on both of them");
                     }