Force warnings even when can_emit_warnings == false

compiler/rustc_errors/src/diagnostic.rs

@@ -29,7 +29,7 @@ pub struct Diagnostic {
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
 pub enum DiagnosticId {
     Error(String),
-    Lint { name: String, has_future_breakage: bool },
+    Lint { name: String, has_future_breakage: bool, is_force_warn: bool },
 }
 
 /// A "sub"-diagnostic attached to a parent diagnostic.
@@ -109,6 +109,13 @@ impl Diagnostic {
         }
     }
 
+    pub fn is_force_warn(&self) -> bool {
+        match self.code {
+            Some(DiagnosticId::Lint { is_force_warn, .. }) => is_force_warn,
+            _ => false,
+        }
+    }
+
     /// Cancel the diagnostic (a structured diagnostic must either be emitted or
     /// canceled or it will panic when dropped).
     pub fn cancel(&mut self) {