Fix typo in E0308 if/else label

Author: estebank

src/librustc/infer/error_reporting/mod.rs

@@ -1650,7 +1650,7 @@ impl<'tcx> ObligationCause<'tcx> {
                 hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have compatible types",
                 _ => "match arms have compatible types",
             },
-            IfExpression { .. } => "if and else have compatible types",
+            IfExpression { .. } => "if and else have incompatible types",
             IfExpressionWithNoElse => "if missing an else returns ()",
             MainFunctionType => "`main` function has the correct type",
             StartFunctionType => "`start` function has the correct type",

src/librustc/ty/error.rs

@@ -247,20 +247,31 @@ impl<'tcx> ty::TyS<'tcx> {
 }
 
 impl<'tcx> TyCtxt<'tcx> {
-    pub fn note_and_explain_type_err(self,
-                                     db: &mut DiagnosticBuilder<'_>,
-                                     err: &TypeError<'tcx>,
-                                     sp: Span) {
+    pub fn note_and_explain_type_err(
+        self,
+        db: &mut DiagnosticBuilder<'_>,
+        err: &TypeError<'tcx>,
+        sp: Span,
+    ) {
         use self::TypeError::*;
 
-        match err.clone() {
+        match err {
             Sorts(values) => {
                 let expected_str = values.expected.sort_string(self);
                 let found_str = values.found.sort_string(self);
                 if expected_str == found_str && expected_str == "closure" {
                     db.note("no two closures, even if identical, have the same type");
                     db.help("consider boxing your closure and/or using it as a trait object");
                 }
+                if expected_str == found_str && expected_str == "opaque type" { // Issue #63167
+                    db.note("distinct uses of `impl Trait` result in different opaque types");
+                    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" {
+                        db.help("if both futures resolve to the same type, consider `await`ing \
+                                 on both of them");
+                    }
+                }
                 if let (ty::Infer(ty::IntVar(_)), ty::Float(_)) =
                        (&values.found.sty, &values.expected.sty) // Issue #53280
                 {