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, 59 insertions, 0 deletions

diff --git a/gcc/objc/objc-act.cc b/gcc/objc/objc-act.cc
index fe19aa5..02ed6d9 100644
--- a/gcc/objc/objc-act.cc
+++ b/gcc/objc/objc-act.cc
@@ -10340,5 +10340,51 @@ objc_common_init_ts (void)
   MARK_TS_TYPED (PROPERTY_REF);
 }
 
+/* Information for Objective-C-specific features known to __has_feature.  */
+
+struct objc_feature_info
+{
+  typedef bool (*predicate_t) ();
+
+  const char *ident;
+  predicate_t predicate;
+
+  constexpr objc_feature_info (const char *name)
+    : ident (name), predicate (nullptr) {}
+  constexpr objc_feature_info (const char *name, predicate_t p)
+    : ident (name), predicate (p) {}
+
+  bool has_feature () const
+    {
+      return predicate ? predicate () : true;
+    }
+};
+
+static bool objc_nonfragile_abi_p ()
+{
+  return flag_next_runtime && flag_objc_abi >= 2;
+}
+
+static constexpr objc_feature_info objc_features[] =
+{
+  { "objc_default_synthesize_properties" },
+  { "objc_instancetype" },
+  { "objc_nonfragile_abi", objc_nonfragile_abi_p }
+};
+
+/* Register Objective-C-specific features for __has_feature.  */
+
+void
+objc_common_register_features ()
+{
+  for (unsigned i = 0; i < ARRAY_SIZE (objc_features); i++)
+    {
+      const objc_feature_info *info = objc_features + i;
+      if (!info->has_feature ())
+	continue;
+
+      c_common_register_feature (info->ident, true);
+    }
+}
 
 #include "gt-objc-objc-act.h"
diff --git a/gcc/objc/objc-act.h b/gcc/objc/objc-act.h
index 68f9029..df40127 100644
--- a/gcc/objc/objc-act.h
+++ b/gcc/objc/objc-act.h
@@ -29,6 +29,9 @@ int objc_gimplify_expr (tree *, gimple_seq *, gimple_seq *);
 void objc_common_init_ts (void);
 const char *objc_get_sarif_source_language (const char *);
 
+/* Register features common to Objective-C and Objective-C++.  */
+void objc_common_register_features ();
+
 /* NB: The remaining public functions are prototyped in c-common.h, for the
    benefit of stub-objc.cc and objc-act.cc.  */
 
diff --git a/gcc/objc/objc-lang.cc b/gcc/objc/objc-lang.cc
index 8e56de6..107fb0e 100644
--- a/gcc/objc/objc-lang.cc
+++ b/gcc/objc/objc-lang.cc
@@ -56,6 +56,16 @@ objc_get_sarif_source_language (const char *)
   return "objectivec";
 }
 
+/* Implement c-family hook to add language-specific features
+   for __has_{feature,extension}.  */
+
+void
+c_family_register_lang_features ()
+{
+  objc_common_register_features ();
+  c_register_features ();
+}
+
 /* Lang hook routines common to C and ObjC appear in c-objc-common.cc;
    there should be very few (if any) routines below.  */