gccrs: adds warnings for enums

Adds missing warnings for Enums.

Fixes: #4367

gcc/rust/ChangeLog:

	* checks/lints/rust-lint-scan-deadcode.h: Add warnings for
	Enums.

Signed-off-by: lenny.chiadmi-delage <[email protected]>

Author: Villosse

gcc/rust/checks/lints/rust-lint-scan-deadcode.h

@@ -29,12 +29,13 @@ namespace Rust {
 namespace Analysis {
 
 // Scan item symbols and warn the symbol if it is not in the live_symbols set.
-// There are three kinds of item we should handle in this pass.
+// There are four kinds of item we should handle in this pass.
 // 1. Function item
 // 2. The function item in the impl block without trait
 // 3. StructStruct, e.g., `Struct Foo{one: 1, two: 2}`. Furthermore, the unused
 //    struct fields will be warned too.
 // 4. TupleStruct, e.g., `Struct Foo(i32, i32)`
+// 5. Enum, e.g., `enum Foo { A, B }`
 class ScanDeadcode : public MarkLiveBase
 {
   using Rust::Analysis::MarkLiveBase::visit;
@@ -116,6 +117,19 @@ class ScanDeadcode : public MarkLiveBase
       }
   }
 
+  void visit (HIR::Enum &enm) override
+  {
+    HirId hirId = enm.get_mappings ().get_hirid ();
+    if (should_warn (hirId) && !enm.get_visibility ().is_public ())
+      {
+	bool name_starts_underscore
+	  = enm.get_identifier ().as_string ().at (0) == '_';
+	if (!name_starts_underscore)
+	  rust_warning_at (enm.get_locus (), 0, "enum is never used: %qs",
+			   enm.get_identifier ().as_string ().c_str ());
+      }
+  }
+
   void visit (HIR::ImplBlock &blc) override
   {
     if (blc.has_impl_items ())