[gcc/devel/rust/master] format_args: Allow extraneous commas, improve safety

[Thomas Schwinge via Gcc-cvs]

https://gcc.gnu.org/g:0c6c73c5317111c5ec9cf465b3f6e37fe250a449

commit 0c6c73c5317111c5ec9cf465b3f6e37fe250a449
Author: Arthur Cohen <arthur.co...@embecosm.com>
Date:   Wed Apr 9 14:42:08 2025 +0200

    format_args: Allow extraneous commas, improve safety
    
    gcc/rust/ChangeLog:
    
            * expand/rust-macro-builtins-format-args.cc 
(format_args_parse_arguments): Improve safety,
            allow extra commas after end of argument list.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/format_args_extra_comma.rs: New test.

Diff:
---
 gcc/rust/expand/rust-macro-builtins-format-args.cc |  7 ++++
 .../rust/compile/format_args_extra_comma.rs        | 47 ++++++++++++++++++++++
 2 files changed, 54 insertions(+)

diff --git a/gcc/rust/expand/rust-macro-builtins-format-args.cc 
b/gcc/rust/expand/rust-macro-builtins-format-args.cc
index 3015225f47ce..bb01eba9873b 100644
--- a/gcc/rust/expand/rust-macro-builtins-format-args.cc
+++ b/gcc/rust/expand/rust-macro-builtins-format-args.cc
@@ -55,6 +55,8 @@ format_args_parse_arguments (AST::MacroInvocData &invoc)
   if (parser.peek_current_token ()->get_id () == STRING_LITERAL)
     format_expr = parser.parse_literal_expr ();
 
+  rust_assert (format_expr);
+
   // TODO(Arthur): Clean this up - if we haven't parsed a string literal but a
   // macro invocation, what do we do here? return a tl::unexpected?
   auto format_str = static_cast<AST::LiteralExpr &> (*format_expr)
@@ -81,6 +83,11 @@ format_args_parse_arguments (AST::MacroInvocData &invoc)
     {
       parser.skip_token (COMMA);
 
+      // Check in case of an extraneous comma in the args list, which is
+      // allowed - format_args!("fmt", arg, arg2,)
+      if (parser.peek_current_token ()->get_id () == last_token_id)
+       break;
+
       if (parser.peek_current_token ()->get_id () == IDENTIFIER
          && parser.peek (1)->get_id () == EQUAL)
        {
diff --git a/gcc/testsuite/rust/compile/format_args_extra_comma.rs 
b/gcc/testsuite/rust/compile/format_args_extra_comma.rs
new file mode 100644
index 000000000000..fcc435c074c2
--- /dev/null
+++ b/gcc/testsuite/rust/compile/format_args_extra_comma.rs
@@ -0,0 +1,47 @@
+#![feature(rustc_attrs)]
+
+#[rustc_builtin_macro]
+macro_rules! format_args {
+    () => {};
+}
+
+#[lang = "sized"]
+trait Sized {}
+
+pub mod core {
+    pub mod fmt {
+        pub struct Formatter;
+        pub struct Result;
+
+        pub struct Arguments<'a>;
+
+        impl<'a> Arguments<'a> {
+            pub fn new_v1(_: &'a [&'static str], _: &'a [ArgumentV1<'a>]) -> 
Arguments<'a> {
+                Arguments
+            }
+        }
+
+        pub struct ArgumentV1<'a>;
+
+        impl<'a> ArgumentV1<'a> {
+            pub fn new<'b, T>(_: &'b T, _: fn(&T, &mut Formatter) -> Result) 
-> ArgumentV1 {
+                ArgumentV1
+            }
+        }
+
+        pub trait Display {
+            fn fmt(&self, _: &mut Formatter) -> Result;
+        }
+
+        impl Display for i32 {
+            fn fmt(&self, _: &mut Formatter) -> Result {
+                // { dg-warning "unused name .self." "" { target *-*-* } .-1 }
+                Result
+            }
+        }
+    }
+}
+
+fn main() {
+    let _formatted = format_args!("extra commas {} {}", 15, 14,);
+}