make -freflection cc-1 only and only c++26 mode

Author: changkhothuychung

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -901,4 +901,7 @@ def warn_drv_gcc_install_dir_libstdcxx : Warning<
     "future releases of the clang compiler will prefer GCC installations "
     "containing libstdc++ include directories; '%0' would be chosen over '%1'">,
     InGroup<DiagGroup<"gcc-install-dir-libstdcxx">>;
+
+def err_drv_reflection_requires_cxx26 : Error<
+  "option '%0' is only supported when compiling in C++26 mode">;
 }

clang/include/clang/Options/Options.td

@@ -3696,7 +3696,7 @@ defm application_extension : BoolFOption<"application-extension",
   NegFlag<SetFalse>>;
 defm reflection : BoolFOption<"reflection",
   LangOpts<"Reflection">, DefaultFalse,
-  PosFlag<SetTrue, [], [ClangOption, CC1Option],
+  PosFlag<SetTrue, [], [CC1Option],
           "Enable C++26 reflection">,
   NegFlag<SetFalse>>, ShouldParseIf<cplusplus.KeyPath>;
 defm sized_deallocation : BoolFOption<"sized-deallocation",

clang/lib/Frontend/CompilerInvocation.cpp

@@ -624,6 +624,11 @@ static bool FixupInvocation(CompilerInvocation &Invocation,
     LangOpts.RawStringLiterals = true;
   }
 
+  if (Args.hasArg(OPT_freflection) && !LangOpts.CPlusPlus26) {
+    Diags.Report(diag::err_drv_reflection_requires_cxx26)
+        << Args.getLastArg(options::OPT_freflection)->getAsString(Args);
+  }
+
   LangOpts.NamedLoops =
       Args.hasFlag(OPT_fnamed_loops, OPT_fno_named_loops, LangOpts.C2y);