Add emit_for function in diagnostic

When emmitting a note, previously it was not known if the note was for an error or a
warning. If it was for a warning, then with `-Awarnings` it should not have been print.
The `emit_for` function allows someone to specify which level should determine its visibility.

Author: mvdnes

src/libsyntax/diagnostic.rs

@@ -207,6 +207,14 @@ impl Handler {
         if lvl == Warning && !self.can_emit_warnings { return }
         self.emit.borrow_mut().emit(cmsp, msg, Some(code), lvl);
     }
+    pub fn emit_for(&self,
+                cmsp: Option<(&codemap::CodeMap, Span)>,
+                msg: &str,
+                lvl: Level,
+                for_lvl: Level) {
+        if for_lvl == Warning && !self.can_emit_warnings { return }
+        self.emit.borrow_mut().emit(cmsp, msg, None, lvl);
+    }
     pub fn custom_emit(&self, cm: &codemap::CodeMap,
                        sp: RenderSpan, msg: &str, lvl: Level) {
         if lvl == Warning && !self.can_emit_warnings { return }

src/libsyntax/parse/obsolete.rs

@@ -18,6 +18,7 @@ use codemap::Span;
 use parse::parser;
 use parse::token;
 use ptr::P;
+use diagnostic::{Warning, Error, Note};
 
 /// The specific types of unsupported syntax
 #[derive(Copy, PartialEq, Eq, Hash)]
@@ -87,10 +88,11 @@ impl<'a> ParserObsoleteMethods for parser::Parser<'a> {
         }
 
         if !self.obsolete_set.contains(&kind) {
+            let for_level = if error { Error } else { Warning };
             self.sess
                 .span_diagnostic
                 .handler()
-                .note(&format!("{}", desc));
+                .emit_for(None, &format!("{}", desc), Note, for_level);
             self.obsolete_set.insert(kind);
         }
     }