[gcc r14-8667] c++: add deprecation notice for -fconcepts-ts

[gcc r14-8667] c++: add deprecation notice for -fconcepts-ts

[Marek Polacek]

https://gcc.gnu.org/g:d836db149d439658cb98688f3f5c6ed58446e333

commit r14-8667-gd836db149d439658cb98688f3f5c6ed58446e333
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Jan 30 17:11:34 2024 -0500

    c++: add deprecation notice for -fconcepts-ts
    
    We plan to remove -fconcepts-ts in GCC 15 and thus remove the flag_concepts_ts
    code.  This note is an admonishing reminder to convert the Concepts TS
    code to C++20 Concepts.
    
    gcc/c-family/ChangeLog:
    
            * c-opts.cc (c_common_post_options): Add an inform saying that
            -fconcepts-ts is deprecated and will be removed in GCC 15.
    
    gcc/ChangeLog:
    
            * doc/invoke.texi: Mention that -fconcepts-ts was deprecated in GCC 14.

Diff:
---
 gcc/c-family/c-opts.cc | 5 +++++
 gcc/doc/invoke.texi    | 4 +++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index b38a1225ac43..b845aff2226f 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -1139,6 +1139,11 @@ c_common_post_options (const char **pfilename)
   if (cxx_dialect >= cxx20 || flag_concepts_ts)
     flag_concepts = 1;
 
+  /* -fconcepts-ts will be removed in GCC 15.  */
+  if (flag_concepts_ts)
+    inform (input_location, "%<-fconcepts-ts%> is deprecated and will be "
+	    "removed in GCC 15; please convert your code to C++20 concepts");
+
   /* -fimmediate-escalation has no effect when immediate functions are not
      supported.  */
   if (flag_immediate_escalation && cxx_dialect < cxx20)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index eb931b984e8f..ca2c0e90452d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -3204,7 +3204,9 @@ the language standard, so @option{-fconcepts} defaults to on.
 Some constructs that were allowed by the earlier C++ Extensions for
 Concepts Technical Specification, ISO 19217 (2015), but didn't make it
 into the standard, can additionally be enabled by
-@option{-fconcepts-ts}.
+@option{-fconcepts-ts}.  The option @option{-fconcepts-ts} was deprecated
+in GCC 14 and may be removed in GCC 15; users are expected to convert
+their code to C++20 concepts.
 
 @opindex fconstexpr-depth
 @item -fconstexpr-depth=@var{n}