[gcc r17-3110] gccrs: add unused braces lint

https://gcc.gnu.org/g:414d7946327e2b9c4b73b35b43024b1c411b5ced

commit r17-3110-g414d7946327e2b9c4b73b35b43024b1c411b5ced
Author: Lucas Ly Ba <[email protected]>
Date:   Fri Jun 26 22:33:18 2026 +0200

    gccrs: add unused braces lint
    
    gcc/rust/ChangeLog:
    
            * checks/lints/unused/rust-unused-checker.cc (UnusedChecker::visit):
            Warn on unnecessary braces around an assigned value.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/unused-braces_0.rs: New test.
    
    Signed-off-by: Lucas Ly Ba <[email protected]>

Diff:
---
 gcc/rust/checks/lints/unused/rust-unused-checker.cc | 9 +++++++++
 gcc/testsuite/rust/compile/unused-braces_0.rs       | 8 ++++++++
 2 files changed, 17 insertions(+)

diff --git a/gcc/rust/checks/lints/unused/rust-unused-checker.cc b/gcc/rust/checks/lints/unused/rust-unused-checker.cc
index 14e2df8dac87..2c521634d8b7 100644
--- a/gcc/rust/checks/lints/unused/rust-unused-checker.cc
+++ b/gcc/rust/checks/lints/unused/rust-unused-checker.cc
@@ -330,6 +330,15 @@ UnusedChecker::visit (HIR::LetStmt &stmt)
 			 "unused doc comment");
 	break;
       }
+  if (stmt.has_init_expr ()
+      && stmt.get_init_expr ().get_expression_type ()
+	   == HIR::Expr::ExprType::Block)
+    {
+      auto &block = static_cast<HIR::BlockExpr &> (stmt.get_init_expr ());
+      if (block.get_statements ().empty () && block.has_expr ())
+	rust_warning_at (block.get_locus (), OPT_Wunused,
+			 "unnecessary braces around assigned value");
+    }
   walk (stmt);
 }
 
diff --git a/gcc/testsuite/rust/compile/unused-braces_0.rs b/gcc/testsuite/rust/compile/unused-braces_0.rs
new file mode 100644
index 000000000000..d1cd3bbdf95e
--- /dev/null
+++ b/gcc/testsuite/rust/compile/unused-braces_0.rs
@@ -0,0 +1,8 @@
+// { dg-additional-options "-frust-unused-check-2.0" }
+#![feature(no_core)]
+#![no_core]
+
+pub fn foo() {
+    let _x = { 5 };
+// { dg-warning "unnecessary braces around assigned value" "" { target *-*-* } .-1 }
+}