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

compiler/rustc_errors/src/emitter.rs

@@ -212,7 +212,12 @@ fn emit_artifact_notification(&mut self, _path: &Path, _artifact_type: &str) {}
     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 @@ fn emit_future_breakage_report(&mut self, diags: Vec<crate::Diagnostic>) {
         }
     }
 
-    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 @@ pub fn emit_future_breakage_report(&self, diags: Vec<Diagnostic>) {
         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 @@ fn emit_artifact_notification(&mut self, path: &Path, artifact_type: &str) {
         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);
     }
 

compiler/rustc_lint_defs/src/lib.rs

@@ -214,6 +214,13 @@ pub fn from_attr(attr: &Attribute) -> Option<Level> {
             _ => None,
         }
     }
+
+    pub fn is_error(self) -> bool {
+        match self {
+            Level::Allow | Level::Expect(_) | Level::Warn | Level::ForceWarn => false,
+            Level::Deny | Level::Forbid => true,
+        }
+    }
 }
 
 /// Specification of a single lint.

compiler/rustc_metadata/src/creader.rs

@@ -208,10 +208,7 @@ pub fn report_unused_deps(&self, tcx: TyCtxt<'_>) {
             let unused_externs =
                 self.unused_externs.iter().map(|ident| ident.to_ident_string()).collect::<Vec<_>>();
             let unused_externs = unused_externs.iter().map(String::as_str).collect::<Vec<&str>>();
-            tcx.sess
-                .parse_sess
-                .span_diagnostic
-                .emit_unused_externs(level.as_str(), &unused_externs);
+            tcx.sess.parse_sess.span_diagnostic.emit_unused_externs(level, &unused_externs);
         }
     }
 }