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>

8 files changed, 420 insertions, 0 deletions

diff --git a/gcc/testsuite/c-c++-common/has-feature-common.c b/gcc/testsuite/c-c++-common/has-feature-common.c
new file mode 100644
index 0000000..1604d77
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/has-feature-common.c
@@ -0,0 +1,73 @@
+/* { dg-do compile } */
+/* Test __has_{feature,extension} for generic features.  */
+
+#define FEAT(x) (__has_feature (x) && __has_extension (x))
+#define EXT(x) (__has_extension (x) && !__has_feature (x))
+
+#if __has_feature (unknown_feature) || __has_extension (unknown_feature)
+#error unknown feature is known!
+#endif
+
+#if !EXT (gnu_asm_goto_with_outputs)
+#error
+#endif
+
+#if !EXT (__gnu_asm_goto_with_outputs__)
+#error
+#endif
+
+#if !EXT (gnu_asm_goto_with_outputs_full)
+#error
+#endif
+
+#if !EXT (__gnu_asm_goto_with_outputs_full__)
+#error
+#endif
+
+#if !FEAT (enumerator_attributes)
+#error
+#endif
+
+#if !FEAT (__enumerator_attributes__)
+#error
+#endif
+
+#if !FEAT (attribute_deprecated_with_message)
+#error
+#endif
+
+#if !FEAT (__attribute_deprecated_with_message__)
+#error
+#endif
+
+#if !FEAT (attribute_unavailable_with_message)
+#error
+#endif
+
+#if !FEAT (__attribute_unavailable_with_message__)
+#error
+#endif
+
+#if !FEAT (tls)
+#error
+#endif
+
+#if !FEAT(__tls__)
+#error
+#endif
+
+#if defined (__SANITIZE_ADDRESS__) != __has_feature (address_sanitizer)
+#error
+#endif
+
+#if defined (__SANITIZE_ADDRESS__) != __has_extension (address_sanitizer)
+#error
+#endif
+
+#if defined (__SANITIZE_THREAD__) != __has_feature (thread_sanitizer)
+#error
+#endif
+
+#if defined (__SANITIZE_THREAD__) != __has_extension (thread_sanitizer)
+#error
+#endif
diff --git a/gcc/testsuite/c-c++-common/has-feature-pedantic.c b/gcc/testsuite/c-c++-common/has-feature-pedantic.c
new file mode 100644
index 0000000..4ac16a4
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/has-feature-pedantic.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-pedantic-errors" } */
+
+/* When -pedantic-errors is passed, __has_extension should behave like
+   __has_feature.  */
+
+#if __has_feature (gnu_asm_goto_with_outputs)
+#error extension recognized as feature
+#endif
+
+#if __has_extension (gnu_asm_goto_with_outputs)
+#error pure extensions should not be recognized with -pedantic-errors
+#endif
+
+#if !__has_feature (tls) || !__has_extension (tls)
+#error features should still be recognized with -pedantic-errors
+#endif
+
+/* Make this TU non-empty to appease -pedantic-errors.  */
+int foo;
diff --git a/gcc/testsuite/g++.dg/ext/has-feature.C b/gcc/testsuite/g++.dg/ext/has-feature.C
new file mode 100644
index 0000000..52191b7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/has-feature.C
@@ -0,0 +1,206 @@
+// { dg-do compile }
+// { dg-options "" }
+
+#define FEAT(x) (__has_feature(x) && __has_extension(x))
+#define CXX11 (__cplusplus >= 201103L)
+#define CXX14 (__cplusplus >= 201402L)
+
+#if !FEAT(cxx_exceptions) || !FEAT(cxx_rtti)
+#error
+#endif
+
+#if __has_feature (cxx_access_control_sfinae) != CXX11
+#error
+#endif
+
+#if !__has_extension (cxx_access_control_sfinae)
+#error
+#endif
+
+#if FEAT(cxx_alias_templates) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_alignas) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_alignof) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_attributes) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_constexpr) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_decltype) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_decltype_incomplete_return_types) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_default_function_template_args) != CXX11
+#error
+#endif
+
+#if FEAT(cxx_defaulted_functions) != CXX11
+#error
+#endif
+
+#if __has_feature (cxx_delegating_constructors) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_deleted_functions) != CXX11
+#error
+#endif
+
+#if __has_feature (cxx_explicit_conversions) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_generalized_initializers) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_implicit_moves) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_inheriting_constructors) != CXX11
+#error
+#endif
+
+#if !__has_extension (cxx_inline_namespaces)
+#error
+#endif
+
+#if __has_feature (cxx_inline_namespaces) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_lambdas) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_local_type_template_args) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_noexcept) != CXX11
+#error
+#endif
+
+#if __has_feature (cxx_nonstatic_member_init) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_nullptr) != CXX11
+#error
+#endif
+
+#if __has_feature (cxx_override_control) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_reference_qualified_functions) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_range_for) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_raw_string_literals) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_rvalue_references) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_static_assert) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_thread_local) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_auto_type) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_strong_enums) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_trailing_return) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_unicode_literals) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_unrestricted_unions) != CXX11
+#error
+#endif
+
+#if FEAT (cxx_user_literals) != CXX11
+#error
+#endif
+
+#if !__has_extension (cxx_variadic_templates)
+#error
+#endif
+
+#if __has_feature (cxx_variadic_templates) != CXX11
+#error
+#endif
+
+#if !__has_extension (cxx_binary_literals)
+#error
+#endif
+
+#if __has_feature (cxx_binary_literals) != CXX14
+#error
+#endif
+
+#if FEAT (cxx_decltype_auto) != CXX14
+#error
+#endif
+
+#if FEAT (cxx_aggregate_nsdmi) != CXX14
+#error
+#endif
+
+#if __has_extension (cxx_init_captures) != CXX11
+#error
+#endif
+
+#if __has_feature (cxx_init_captures) != CXX14
+#error
+#endif
+
+#if FEAT (cxx_generic_lambdas) != CXX14
+#error
+#endif
+
+#if FEAT (cxx_relaxed_constexpr) != CXX14
+#error
+#endif
+
+#if FEAT (cxx_return_type_deduction) != CXX14
+#error
+#endif
+
+#if __has_feature (cxx_variable_templates) != CXX14
+#error
+#endif
diff --git a/gcc/testsuite/gcc.dg/asan/has-feature-asan.c b/gcc/testsuite/gcc.dg/asan/has-feature-asan.c
new file mode 100644
index 0000000..810b69b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/asan/has-feature-asan.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-fsanitize=address" } */
+#define FEAT(x) (__has_feature (x) && __has_extension (x))
+#if !FEAT (address_sanitizer)
+#error
+#endif
diff --git a/gcc/testsuite/gcc.dg/has-feature.c b/gcc/testsuite/gcc.dg/has-feature.c
new file mode 100644
index 0000000..2fd0b4c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/has-feature.c
@@ -0,0 +1,62 @@
+/* { dg-do compile } */
+/* { dg-options "" } */
+/* Test __has_{feature,extension} for C language features.  */
+
+#if !__has_extension (c_alignas) || !__has_extension (c_alignof)
+#error
+#endif
+
+#if !__has_extension (c_atomic) || !__has_extension (c_generic_selections)
+#error
+#endif
+
+#if !__has_extension (c_static_assert) || !__has_extension (c_thread_local)
+#error
+#endif
+
+#if !__has_extension (cxx_binary_literals)
+#error
+#endif
+
+#if  __STDC_VERSION__ >= 201112L
+/* Have C11 features.  */
+#if !__has_feature (c_alignas) || !__has_feature (c_alignof)
+#error
+#endif
+
+#if !__has_feature (c_atomic) || !__has_feature (c_generic_selections)
+#error
+#endif
+
+#if !__has_feature (c_static_assert) || !__has_feature (c_thread_local)
+#error
+#endif
+
+#else
+/* Don't have C11 features.  */
+#if __has_feature (c_alignas) || __has_feature (c_alignof)
+#error
+#endif
+
+#if __has_feature (c_atomic) || __has_feature (c_generic_selections)
+#error
+#endif
+
+#if __has_feature (c_static_assert) || __has_feature (c_thread_local)
+#error
+#endif
+
+#endif
+
+#if __STDC_VERSION__ >= 202000L
+/* Have C2x features.  */
+#if !__has_feature (cxx_binary_literals)
+#error
+#endif
+
+#else
+/* Don't have C2x features.  */
+#if __has_feature (cxx_binary_literals)
+#error
+#endif
+#endif
diff --git a/gcc/testsuite/gcc.dg/ubsan/has-feature-ubsan.c b/gcc/testsuite/gcc.dg/ubsan/has-feature-ubsan.c
new file mode 100644
index 0000000..e5da1cc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ubsan/has-feature-ubsan.c
@@ -0,0 +1,6 @@
+/* { dg-do compile } */
+/* { dg-options "-fsanitize=undefined" } */
+#define FEAT(x) (__has_feature (x) && __has_extension (x))
+#if !FEAT (undefined_behavior_sanitizer)
+#error
+#endif
diff --git a/gcc/testsuite/obj-c++.dg/has-feature.mm b/gcc/testsuite/obj-c++.dg/has-feature.mm
new file mode 100644
index 0000000..77c7617
--- /dev/null
+++ b/gcc/testsuite/obj-c++.dg/has-feature.mm
@@ -0,0 +1,21 @@
+// { dg-do compile }
+
+#define CXX11 (__cplusplus >= 201103L)
+
+#if !__has_feature (objc_instancetype)
+#error
+#endif
+
+#if !__has_feature (objc_default_synthesize_properties)
+#error
+#endif
+
+// C features should not be available.
+#if __has_extension (c_alignas) || __has_feature (c_alignof)
+#error
+#endif
+
+// C++ features should be available (given the right standard).
+#if __has_feature (cxx_constexpr) != CXX11
+#error
+#endif
diff --git a/gcc/testsuite/objc.dg/has-feature.m b/gcc/testsuite/objc.dg/has-feature.m
new file mode 100644
index 0000000..168b0ce
--- /dev/null
+++ b/gcc/testsuite/objc.dg/has-feature.m
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+
+#define HAVE_C11 (__STDC_VERSION__ >= 201112L)
+
+#if !__has_feature (objc_instancetype)
+#error
+#endif
+
+#if !__has_feature (objc_default_synthesize_properties)
+#error
+#endif
+
+/* C features should be available as extensions.  */
+#if !__has_extension (c_alignas)
+#error
+#endif
+
+/* And as features given the appropriate C standard.  */
+#if __has_feature (c_alignas) != HAVE_C11
+#error
+#endif
+
+/* Shouldn't have C++ features even as extensions.  */
+#if __has_feature (cxx_constexpr) || __has_extension (cxx_constexpr)
+#error
+#endif