[gcc r15-8767] gccrs: scan-deadcode: Do not warn unused fields if they start with '_'

[Arthur Cohen]

https://gcc.gnu.org/g:ee93fe2c991c81b664855d510e6d721c101689d9

commit r15-8767-gee93fe2c991c81b664855d510e6d721c101689d9
Author: Arthur Cohen <arthur.cohen@embecosm.com>
Date:   Thu Jan 30 13:08:33 2025 +0100

    gccrs: scan-deadcode: Do not warn unused fields if they start with '_'
    
    gcc/rust/ChangeLog:
    
            * checks/lints/rust-lint-scan-deadcode.h: Check if the field name starts with an
            underscore before warning.

Diff:
---
 gcc/rust/checks/lints/rust-lint-scan-deadcode.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/checks/lints/rust-lint-scan-deadcode.h b/gcc/rust/checks/lints/rust-lint-scan-deadcode.h
index e6ef1392c89e..0fc203b03189 100644
--- a/gcc/rust/checks/lints/rust-lint-scan-deadcode.h
+++ b/gcc/rust/checks/lints/rust-lint-scan-deadcode.h
@@ -93,7 +93,8 @@ public:
 	  {
 	    HirId field_hir_id = field.get_mappings ().get_hirid ();
 	    if (should_warn (field_hir_id)
-		&& !field.get_visibility ().is_public ())
+		&& !field.get_visibility ().is_public ()
+		&& field.get_field_name ().as_string ().at (0) != '_')
 	      {
 		rust_warning_at (field.get_locus (), 0,
 				 "field is never read: %qs",