Add runtime check to avoid overwrite arg easily in diag and store and restore snapshot when set subdiag arg

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

compiler/rustc_passes/src/errors.rs

@@ -1509,7 +1509,7 @@ pub(crate) struct EnumVariantSameName<'tcx> {
     #[primary_span]
     pub variant_span: Span,
     pub dead_name: Symbol,
-    pub descr: &'tcx str,
+    pub dead_descr: &'tcx str,
 }
 
 #[derive(Subdiagnostic)]
@@ -1707,6 +1707,7 @@ impl Subdiagnostic for UnusedVariableStringInterp {
 #[derive(LintDiagnostic)]
 #[diag(passes_unused_variable_try_ignore)]
 pub(crate) struct UnusedVarTryIgnore {
+    pub name: String,
     #[subdiagnostic]
     pub sugg: UnusedVarTryIgnoreSugg,
 }