c-family: Implement __has_feature and __has_extension [PR60512]

This patch implements clang's __has_feature and __has_extension in GCC.
Currently the patch aims to implement all documented features (and some
undocumented ones) following the documentation at
https://clang.llvm.org/docs/LanguageExtensions.html with the exception
of the legacy features for C++ type traits.  These are omitted, since as
the clang documentation notes, __has_builtin is the correct "modern" way
to query for these (which GCC already implements).

gcc/c-family/ChangeLog:

	PR c++/60512
	* c-common.cc (struct hf_feature_info): New.
	(c_common_register_feature): New.
	(init_has_feature): New.
	(has_feature_p): New.
	* c-common.h (c_common_has_feature): New.
	(c_family_register_lang_features): New.
	(c_common_register_feature): New.
	(has_feature_p): New.
	* c-lex.cc (init_c_lex): Plumb through has_feature callback.
	(c_common_has_builtin): Generalize and move common part ...
	(c_common_lex_availability_macro): ... here.
	(c_common_has_feature): New.
	* c-ppoutput.cc (init_pp_output): Plumb through has_feature.

gcc/c/ChangeLog:

	PR c++/60512
	* c-lang.cc (c_family_register_lang_features): New.
	* c-objc-common.cc (struct c_feature_info): New.
	(c_register_features): New.
	* c-objc-common.h (c_register_features): New.

gcc/cp/ChangeLog:

	PR c++/60512
	* cp-lang.cc (c_family_register_lang_features): New.
	* cp-objcp-common.cc (struct cp_feature_selector): New.
	(cp_feature_selector::has_feature): New.
	(struct cp_feature_info): New.
	(cp_register_features): New.
	* cp-objcp-common.h (cp_register_features): New.

gcc/ChangeLog:

	PR c++/60512
	* doc/cpp.texi: Document __has_{feature,extension}.

gcc/objc/ChangeLog:

	PR c++/60512
	* objc-act.cc (struct objc_feature_info): New.
	(objc_nonfragile_abi_p): New.
	(objc_common_register_features): New.
	* objc-act.h (objc_common_register_features): New.
	* objc-lang.cc (c_family_register_lang_features): New.

gcc/objcp/ChangeLog:

	PR c++/60512
	* objcp-lang.cc (c_family_register_lang_features): New.

libcpp/ChangeLog:

	PR c++/60512
	* include/cpplib.h (struct cpp_callbacks): Add has_feature.
	(enum cpp_builtin_type): Add BT_HAS_{FEATURE,EXTENSION}.
	* init.cc: Add __has_{feature,extension}.
	* macro.cc (_cpp_builtin_macro_text): Handle
	BT_HAS_{FEATURE,EXTENSION}.

gcc/testsuite/ChangeLog:

	PR c++/60512
	* c-c++-common/has-feature-common.c: New test.
	* c-c++-common/has-feature-pedantic.c: New test.
	* g++.dg/ext/has-feature.C: New test.
	* gcc.dg/asan/has-feature-asan.c: New test.
	* gcc.dg/has-feature.c: New test.
	* gcc.dg/ubsan/has-feature-ubsan.c: New test.
	* obj-c++.dg/has-feature.mm: New test.
	* objc.dg/has-feature.m: New test.

Co-Authored-By: Iain Sandoe <iain@sandoe.co.uk>

3 files changed, 14 insertions, 1 deletions

diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index f857ffa..2b66262 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -764,6 +764,9 @@ struct cpp_callbacks
   /* Callback to determine whether a built-in function is recognized.  */
   int (*has_builtin) (cpp_reader *);
 
+  /* Callback to determine whether a feature is available.  */
+  int (*has_feature) (cpp_reader *, bool);
+
   /* Callback that can change a user lazy into normal macro.  */
   void (*user_lazy_macro) (cpp_reader *, cpp_macro *, unsigned);
 
@@ -968,7 +971,9 @@ enum cpp_builtin_type
   BT_HAS_STD_ATTRIBUTE,		/* `__has_c_attribute(x)' */
   BT_HAS_BUILTIN,		/* `__has_builtin(x)' */
   BT_HAS_INCLUDE,		/* `__has_include(x)' */
-  BT_HAS_INCLUDE_NEXT		/* `__has_include_next(x)' */
+  BT_HAS_INCLUDE_NEXT,		/* `__has_include_next(x)' */
+  BT_HAS_FEATURE,		/* `__has_feature(x)' */
+  BT_HAS_EXTENSION		/* `__has_extension(x)' */
 };
 
 #define CPP_HASHNODE(HNODE)	((cpp_hashnode *) (HNODE))
diff --git a/libcpp/init.cc b/libcpp/init.cc
index 250a02a..5dfce4b 100644
--- a/libcpp/init.cc
+++ b/libcpp/init.cc
@@ -435,6 +435,8 @@ static const struct builtin_macro builtin_array[] =
   B("__has_builtin",	 BT_HAS_BUILTIN,   true),
   B("__has_include",	 BT_HAS_INCLUDE,   true),
   B("__has_include_next",BT_HAS_INCLUDE_NEXT,   true),
+  B("__has_feature",	 BT_HAS_FEATURE, true),
+  B("__has_extension",	 BT_HAS_EXTENSION, true),
   /* Keep builtins not used for -traditional-cpp at the end, and
      update init_builtins() if any more are added.  */
   B("_Pragma",		 BT_PRAGMA,        true),
diff --git a/libcpp/macro.cc b/libcpp/macro.cc
index f437da4..6f24a9d 100644
--- a/libcpp/macro.cc
+++ b/libcpp/macro.cc
@@ -677,6 +677,12 @@ _cpp_builtin_macro_text (cpp_reader *pfile, cpp_hashnode *node,
       number = builtin_has_include (pfile, node,
 				    node->value.builtin == BT_HAS_INCLUDE_NEXT);
       break;
+
+    case BT_HAS_FEATURE:
+    case BT_HAS_EXTENSION:
+      number = pfile->cb.has_feature (pfile,
+				      node->value.builtin == BT_HAS_FEATURE);
+      break;
     }
 
   if (result == NULL)