Remove LabelKind.

It has three variants, but only `LabelKind::Label` is ever used. This
means `SingleLabelManySpans::kind` can also be removed.

Author: nnethercote

compiler/rustc_builtin_macros/src/format.rs

@@ -883,7 +883,6 @@ fn report_invalid_references(
             highlight: SingleLabelManySpans {
                 spans: args.explicit_args().iter().map(|arg| arg.expr.span).collect(),
                 label: "",
-                kind: rustc_errors::LabelKind::Label,
             },
         });
         // Point out `{:.*}` placeholders: those take an extra argument.

compiler/rustc_errors/src/diagnostic_impls.rs

@@ -312,25 +312,13 @@ impl<G: EmissionGuarantee> IntoDiagnostic<'_, G> for TargetDataLayoutErrors<'_>
 pub struct SingleLabelManySpans {
     pub spans: Vec<Span>,
     pub label: &'static str,
-    pub kind: LabelKind,
 }
 impl AddToDiagnostic for SingleLabelManySpans {
     fn add_to_diagnostic_with<F>(self, diag: &mut crate::Diagnostic, _: F) {
-        match self.kind {
-            LabelKind::Note => diag.span_note(self.spans, self.label),
-            LabelKind::Label => diag.span_labels(self.spans, self.label),
-            LabelKind::Help => diag.span_help(self.spans, self.label),
-        };
+        diag.span_labels(self.spans, self.label);
     }
 }
 
-/// The kind of label to attach when using [`SingleLabelManySpans`]
-pub enum LabelKind {
-    Note,
-    Label,
-    Help,
-}
-
 #[derive(Subdiagnostic)]
 #[label(errors_expected_lifetime_parameter)]
 pub struct ExpectedLifetimeParameter {

compiler/rustc_errors/src/lib.rs

@@ -36,8 +36,7 @@ pub use diagnostic_builder::{
 };
 pub use diagnostic_impls::{
     DiagnosticArgFromDisplay, DiagnosticSymbolList, ExpectedLifetimeParameter,
-    IndicateAnonymousLifetime, InvalidFlushedDelayedDiagnosticLevel, LabelKind,
-    SingleLabelManySpans,
+    IndicateAnonymousLifetime, InvalidFlushedDelayedDiagnosticLevel, SingleLabelManySpans,
 };
 pub use emitter::ColorConfig;
 pub use rustc_error_messages::{