Plumb through rustc_lint_defs::Level as enum rather than string.

compiler/rustc_errors/src/emitter.rs

@@ -212,7 +212,12 @@ pub trait Emitter {
     fn emit_future_breakage_report(&mut self, _diags: Vec<Diagnostic>) {}
 
     /// Emit list of unused externs
-    fn emit_unused_externs(&mut self, _lint_level: &str, _unused_externs: &[&str]) {}
+    fn emit_unused_externs(
+        &mut self,
+        _lint_level: rustc_lint_defs::Level,
+        _unused_externs: &[&str],
+    ) {
+    }
 
     /// Checks if should show explanations about "rustc --explain"
     fn should_show_explain(&self) -> bool {

compiler/rustc_errors/src/json.rs

@@ -171,7 +171,8 @@ impl Emitter for JsonEmitter {
         }
     }
 
-    fn emit_unused_externs(&mut self, lint_level: &str, unused_externs: &[&str]) {
+    fn emit_unused_externs(&mut self, lint_level: rustc_lint_defs::Level, unused_externs: &[&str]) {
+        let lint_level = lint_level.as_str();
         let data = UnusedExterns { lint_level, unused_extern_names: unused_externs };
         let result = if self.pretty {
             writeln!(&mut self.dst, "{}", as_pretty_json(&data))

compiler/rustc_errors/src/lib.rs

@@ -969,10 +969,10 @@ impl Handler {
         self.inner.borrow_mut().emitter.emit_future_breakage_report(diags)
     }
 
-    pub fn emit_unused_externs(&self, lint_level: &str, unused_externs: &[&str]) {
+    pub fn emit_unused_externs(&self, lint_level: rustc_lint_defs::Level, unused_externs: &[&str]) {
         let mut inner = self.inner.borrow_mut();
 
-        if lint_level == "deny" || lint_level == "forbid" {
+        if lint_level.is_error() {
             inner.bump_err_count();
         }
 
@@ -1147,7 +1147,7 @@ impl HandlerInner {
         self.emitter.emit_artifact_notification(path, artifact_type);
     }
 
-    fn emit_unused_externs(&mut self, lint_level: &str, unused_externs: &[&str]) {
+    fn emit_unused_externs(&mut self, lint_level: rustc_lint_defs::Level, unused_externs: &[&str]) {
         self.emitter.emit_unused_externs(lint_level, unused_externs);
     }