[gcc r17-3103] gccrs: Fix duplicate "trailing semicolon in macro used" warnings

https://gcc.gnu.org/g:1bf052967ce09aca7cb20b35a85b7e4a07f147d7

commit r17-3103-g1bf052967ce09aca7cb20b35a85b7e4a07f147d7
Author: Yap Zhi Heng <[email protected]>
Date:   Mon Jul 6 19:51:31 2026 +0800

    gccrs: Fix duplicate "trailing semicolon in macro used" warnings
    
    gcc/rust/ChangeLog:
    
            * expand/rust-macro-expand.cc (transcribe_expression (Parser<MacroInvocLexer>)):
            Prevent the same trailing semicolon warning from being generated at the same loc.
    
    Signed-Off-By: Yap Zhi Heng <[email protected]>

Diff:
---
 gcc/rust/expand/rust-macro-expand.cc | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/gcc/rust/expand/rust-macro-expand.cc b/gcc/rust/expand/rust-macro-expand.cc
index 2ab9d2541dcb..30373722e8c8 100644
--- a/gcc/rust/expand/rust-macro-expand.cc
+++ b/gcc/rust/expand/rust-macro-expand.cc
@@ -1012,9 +1012,14 @@ transcribe_expression (Parser<MacroInvocLexer> &parser)
   // FIXME: make this an error for some edititons
   if (parser.peek_current_token ()->get_id () == SEMICOLON)
     {
-      rust_warning_at (
-	parser.peek_current_token ()->get_locus (), 0,
-	"trailing semicolon in macro used in expression context");
+      // TODO bandaid for now, make this a member for MacroExpander instead in
+      // the future
+      static std::unordered_set<location_t> warned_loc;
+      auto locus = parser.peek_current_token ()->get_locus ();
+      if (warned_loc.insert (locus).second)
+	rust_warning_at (
+	  parser.peek_current_token ()->get_locus (), 0,
+	  "trailing semicolon in macro used in expression context");
       parser.skip_token ();
     }