privacy: Avoid some unnecessary mutability

Author: petrochenkov

compiler/rustc_privacy/src/lib.rs

@@ -929,7 +929,7 @@ impl<'tcx> NamePrivacyVisitor<'tcx> {
 
     // Checks that a field in a struct constructor (expression or pattern) is accessible.
     fn check_field(
-        &mut self,
+        &self,
         hir_id: hir::HirId,    // ID of the field use
         use_ctxt: Span,        // syntax context of the field name at the use site
         def: ty::AdtDef<'tcx>, // definition of the struct or enum
@@ -947,7 +947,7 @@ impl<'tcx> NamePrivacyVisitor<'tcx> {
 
     // Checks that a field in a struct constructor (expression or pattern) is accessible.
     fn emit_unreachable_field_error(
-        &mut self,
+        &self,
         fields: Vec<(Symbol, Span, bool /* field is present */)>,
         def: ty::AdtDef<'tcx>, // definition of the struct or enum
         update_syntax: Option<Span>,
@@ -1010,7 +1010,7 @@ impl<'tcx> NamePrivacyVisitor<'tcx> {
     }
 
     fn check_expanded_fields(
-        &mut self,
+        &self,
         adt: ty::AdtDef<'tcx>,
         variant: &'tcx ty::VariantDef,
         fields: &[hir::ExprField<'tcx>],
@@ -1148,7 +1148,7 @@ impl<'tcx> TypePrivacyVisitor<'tcx> {
         result.is_break()
     }
 
-    fn check_def_id(&mut self, def_id: DefId, kind: &str, descr: &dyn fmt::Display) -> bool {
+    fn check_def_id(&self, def_id: DefId, kind: &str, descr: &dyn fmt::Display) -> bool {
         let is_error = !self.item_is_accessible(def_id);
         if is_error {
             self.tcx.dcx().emit_err(ItemIsPrivate { span: self.span, kind, descr: descr.into() });
@@ -1405,7 +1405,7 @@ impl SearchInterfaceForPrivateItemsVisitor<'_> {
         self
     }
 
-    fn check_def_id(&mut self, def_id: DefId, kind: &str, descr: &dyn fmt::Display) -> bool {
+    fn check_def_id(&self, def_id: DefId, kind: &str, descr: &dyn fmt::Display) -> bool {
         if self.leaks_private_dep(def_id) {
             self.tcx.emit_node_span_lint(
                 lint::builtin::EXPORTED_PRIVATE_DEPENDENCIES,