Fixed bug calling .note() instead of .help(). Added small note when two

different closures fail typechecking.

See #24036

src/librustc/middle/infer/error_reporting.rs

@@ -812,7 +812,7 @@ impl<'a, 'tcx> ErrorReporting<'tcx> for InferCtxt<'a, 'tcx> {
         }
         self.give_suggestion(same_regions);
         for &(ref trace, terr) in trace_origins {
-            self.report_type_error(trace.clone(), &terr);
+            self.report_and_explain_type_error(trace.clone(), &terr);
         }
     }
 

src/librustc/middle/ty.rs

@@ -5096,7 +5096,7 @@ pub fn type_err_to_str<'tcx>(cx: &ctxt<'tcx>, err: &type_err<'tcx>) -> String {
     }
 }
 
-pub fn note_and_explain_type_err(cx: &ctxt, err: &type_err) {
+pub fn note_and_explain_type_err<'tcx>(cx: &ctxt<'tcx>, err: &type_err<'tcx>) {
     match *err {
         terr_regions_does_not_outlive(subregion, superregion) => {
             note_and_explain_region(cx, "", subregion, "...");
@@ -5127,6 +5127,14 @@ pub fn note_and_explain_type_err(cx: &ctxt, err: &type_err) {
                                     "expected concrete lifetime is ",
                                     conc_region, "");
         }
+        terr_sorts(values) => {
+            let expected_str = ty_sort_string(cx, values.expected);
+            let found_str = ty_sort_string(cx, values.found);
+            if expected_str == found_str && expected_str == "closure" {
+                cx.sess.note(&format!("no two closures, even if identical, have the same type"));
+                cx.sess.help(&format!("consider boxing your closure and/or using it as a trait object"));
+            }
+        }
         _ => {}
     }
 }

src/librustc/session/mod.rs

@@ -155,7 +155,7 @@ impl Session {
         self.diagnostic().handler().note(msg)
     }
     pub fn help(&self, msg: &str) {
-        self.diagnostic().handler().note(msg)
+        self.diagnostic().handler().help(msg)
     }
     pub fn opt_span_bug(&self, opt_sp: Option<Span>, msg: &str) -> ! {
         match opt_sp {