feat(protocol): help is a single Display ref now.

src/protocol.rs

@@ -30,7 +30,7 @@ pub trait Diagnostic: std::error::Error {
 
     /// Additional help text related to this Diagnostic. Do you have any
     /// advice for the poor soul who's just run into this issue?
-    fn help(&self) -> Option<Box<dyn '_ + Iterator<Item = &'_ str>>> {
+    fn help(&self) -> Option<&(dyn Display)> {
         None
     }
 

src/reporter.rs

@@ -131,10 +131,7 @@ impl DiagnosticReporter for MietteReporter {
         }
 
         if let Some(help) = diagnostic.help() {
-            writeln!(f)?;
-            for msg in help {
-                writeln!(f, "﹦{}", msg)?;
-            }
+            writeln!(f,  "﹦{}", help)?;
         }
 
         Ok(())
@@ -162,9 +159,7 @@ impl DiagnosticReporter for JokeReporter {
             diagnostic,
             diagnostic
                 .help()
-                .unwrap_or_else(|| Box::new(vec!["have you tried not failing?"].into_iter()))
-                .collect::<Vec<&str>>()
-                .join(" ")
+                .unwrap_or(&"have you tried not failing?")
         )?;
         writeln!(
             f,

tests/reporter.rs

@@ -23,10 +23,8 @@ impl Diagnostic for MyBad {
         &"oops::my::bad"
     }
 
-    }
-
-    fn help(&self) -> Option<Box<dyn '_ + Iterator<Item = &'_ str>>> {
-        Some(Box::new(vec!["try doing it better next time?"].into_iter()))
+    fn help(&self) -> Option<&(dyn std::fmt::Display)> {
+        Some(&"try doing it better next time?")
     }
 
     fn snippets(&self) -> Option<&[DiagnosticSnippet]> {