[gcc r15-7354] c++: bogus -Wvexing-parse with trailing-return-type [PR118718]

[Marek Polacek via Gcc-cvs]

https://gcc.gnu.org/g:53d1f6cdb5a82e859176e854636400faba0bf0bf

commit r15-7354-g53d1f6cdb5a82e859176e854636400faba0bf0bf
Author: Marek Polacek <pola...@redhat.com>
Date:   Fri Jan 31 14:52:36 2025 -0500

    c++: bogus -Wvexing-parse with trailing-return-type [PR118718]
    
    This warning should not warn for
    
      auto f1 () -> auto;
    
    because that cannot be confused with initializing a variable.
    
            PR c++/118718
    
    gcc/cp/ChangeLog:
    
            * parser.cc (warn_about_ambiguous_parse): Don't warn when a trailing
            return type is present.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wvexing-parse10.C: New test.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/parser.cc                            | 4 ++++
 gcc/testsuite/g++.dg/warn/Wvexing-parse10.C | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 44515bb9074a..1da881e295b4 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -23617,6 +23617,10 @@ warn_about_ambiguous_parse (const 
cp_decl_specifier_seq *decl_specifiers,
                        (const_cast<cp_declarator *>(declarator))))
     return;
 
+  /* Don't warn for auto f () -> auto.  */
+  if (declarator->u.function.late_return_type)
+    return;
+
   /* Don't warn when the whole declarator (not just the declarator-id!)
      was parenthesized.  That is, don't warn for int(n()) but do warn
      for int(f)().  */
diff --git a/gcc/testsuite/g++.dg/warn/Wvexing-parse10.C 
b/gcc/testsuite/g++.dg/warn/Wvexing-parse10.C
new file mode 100644
index 000000000000..3fbe88b7d00b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wvexing-parse10.C
@@ -0,0 +1,9 @@
+// PR c++/118718
+// { dg-do compile { target c++14 } }
+
+void
+fn ()
+{
+  auto f1 () -> auto;
+  auto f2 (); // { dg-warning "empty parentheses" }
+}