[clang] Create new warning group for deprecation of '-fno-relaxed-template-template-args' (llvm#92324)

This allows the warning to be disabled in isolation, as it helps when
treating them as errors.

Author: mizvekov

clang/docs/ReleaseNotes.rst

@@ -51,7 +51,8 @@ C++ Specific Potentially Breaking Changes
 - The behavior controlled by the `-frelaxed-template-template-args` flag is now
   on by default, and the flag is deprecated. Until the flag is finally removed,
   it's negative spelling can be used to obtain compatibility with previous
-  versions of clang.
+  versions of clang. The deprecation warning for the negative spelling can be
+  disabled with `-Wno-deprecated-no-relaxed-template-template-args`.
 
 - Clang now rejects pointer to member from parenthesized expression in unevaluated context such as ``decltype(&(foo::bar))``. (#GH40906).
 

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -436,6 +436,9 @@ def warn_drv_clang_unsupported : Warning<
   "the clang compiler does not support '%0'">;
 def warn_drv_deprecated_arg : Warning<
   "argument '%0' is deprecated%select{|, use '%2' instead}1">, InGroup<Deprecated>;
+def warn_drv_deprecated_arg_no_relaxed_template_template_args : Warning<
+  "argument '-fno-relaxed-template-template-args' is deprecated">,
+  InGroup<DeprecatedNoRelaxedTemplateTemplateArgs>;
 def warn_drv_deprecated_custom : Warning<
   "argument '%0' is deprecated, %1">, InGroup<Deprecated>;
 def warn_drv_assuming_mfloat_abi_is : Warning<

clang/include/clang/Basic/DiagnosticGroups.td

@@ -104,6 +104,7 @@ def EnumConversion : DiagGroup<"enum-conversion",
                                [EnumEnumConversion,
                                 EnumFloatConversion,
                                 EnumCompareConditional]>;
+def DeprecatedNoRelaxedTemplateTemplateArgs : DiagGroup<"deprecated-no-relaxed-template-template-args">;
 def ObjCSignedCharBoolImplicitIntConversion :
   DiagGroup<"objc-signed-char-bool-implicit-int-conversion">;
 def Shorten64To32 : DiagGroup<"shorten-64-to-32">;
@@ -228,6 +229,7 @@ def Deprecated : DiagGroup<"deprecated", [DeprecatedAnonEnumEnumConversion,
                                           DeprecatedLiteralOperator,
                                           DeprecatedPragma,
                                           DeprecatedRegister,
+                                          DeprecatedNoRelaxedTemplateTemplateArgs,
                                           DeprecatedThisCapture,
                                           DeprecatedType,
                                           DeprecatedVolatile,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7253,10 +7253,14 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (Arg *A =
           Args.getLastArg(options::OPT_frelaxed_template_template_args,
                           options::OPT_fno_relaxed_template_template_args)) {
-    D.Diag(diag::warn_drv_deprecated_arg)
-        << A->getAsString(Args) << /*hasReplacement=*/false;
-    if (A->getOption().matches(options::OPT_fno_relaxed_template_template_args))
+    if (A->getOption().matches(
+            options::OPT_fno_relaxed_template_template_args)) {
+      D.Diag(diag::warn_drv_deprecated_arg_no_relaxed_template_template_args);
       CmdArgs.push_back("-fno-relaxed-template-template-args");
+    } else {
+      D.Diag(diag::warn_drv_deprecated_arg)
+          << A->getAsString(Args) << /*hasReplacement=*/false;
+    }
   }
 
   // -fsized-deallocation is off by default, as it is an ABI-breaking change for

clang/test/Driver/frelaxed-template-template-args.cpp

@@ -1,7 +1,9 @@
 // RUN: %clang -fsyntax-only -### %s 2>&1 | FileCheck --check-prefix=CHECK-DEF %s
 // RUN: %clang -fsyntax-only -frelaxed-template-template-args %s 2>&1 | FileCheck --check-prefix=CHECK-ON %s
 // RUN: %clang -fsyntax-only -fno-relaxed-template-template-args %s 2>&1 | FileCheck --check-prefix=CHECK-OFF %s
+// RUN: %clang -fsyntax-only -fno-relaxed-template-template-args -Wno-deprecated-no-relaxed-template-template-args %s 2>&1 | FileCheck --check-prefix=CHECK-DIS --allow-empty %s
 
 // CHECK-DEF-NOT: "-cc1"{{.*}} "-fno-relaxed-template-template-args"
 // CHECK-ON:  warning: argument '-frelaxed-template-template-args' is deprecated [-Wdeprecated]
-// CHECK-OFF: warning: argument '-fno-relaxed-template-template-args' is deprecated [-Wdeprecated]
+// CHECK-OFF: warning: argument '-fno-relaxed-template-template-args' is deprecated [-Wdeprecated-no-relaxed-template-template-args]
+// CHECK-DIS-NOT: warning: argument '-fno-relaxed-template-template-args' is deprecated