0.3.0: converge relibc to upstream 0.6.0 + Red Bear patches

include/features.h

@@ -3,26 +3,93 @@
  * Copyright (c) 2020 Rich Felker musl-libc
  */
 
-#ifndef _FEATURES_H
-#define _FEATURES_H
+#ifndef _FEATURES_H__RELIBC
+#define _FEATURES_H__RELIBC
 
-#if __STDC_VERSION__ >= 199901L
-#define __restrict restrict
-#elif !defined(__GNUC__)
-#define __restrict
+// Version metadata for feature gating
+// This is useful for divergent implementation specific behavior
+// glibc, ulibc, and likely others define a similar macro
+// musl does not define an equivalent macro
+#define __RELIBC__ 1
+#define __RELIBC__MAJOR 0
+#define __RELIBC__MINOR 2
+
+/*
+ * Sources:
+ * https://en.cppreference.com/w/c/language/attributes
+ * https://clang.llvm.org/docs/LanguageExtensions.html
+ * https://gcc.gnu.org/onlinedocs/cpp/_005f_005fhas_005fc_005fattribute.html
+ * https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html
+ */
+
+// Clang doesn't define __has_cpp_attribute if compiling C code
+#if !defined(__has_cpp_attribute)
+    #define __has_cpp_attribute(x) 0
 #endif
 
-#if __STDC_VERSION__ >= 199901L || defined(__cplusplus)
-#define __inline inline
-#elif !defined(__GNUC__)
-#define __inline
+// Clang doesn't define __has_c_attribute if compiling C++ code
+#if !defined(__has_c_attribute)
+    #define __has_c_attribute(x) 0
 #endif
 
-#if __STDC_VERSION__ >= 201112L
-#elif defined(__GNUC__)
-#define _Noreturn __attribute__((__noreturn__))
+// Check if C23+ attributes are available
+#if defined(__cplusplus)
+// HACK: GCC backports C++ attributes to C++98 but doesn't accept attributes
+// placed before the function like cbindgen emits.
+// Let's just disable attributes for C++98 by checking if a random C++11
+// feature is available.
+#define __HAS_ATTRIBUTE(x) __cpp_variable_templates &&__has_cpp_attribute(x)
 #else
-#define _Noreturn
+#define __HAS_ATTRIBUTE(x)                                                     \
+  (__has_c_attribute(x) || __STDC_VERSION__ >= 202311L ||                      \
+   __has_cpp_attribute(x))
+#endif
+
+// TODO: Not emitted with cbindgen
+#if __STDC_VERSION__ >= 199901L
+    #define __restrict restrict
+#elif !defined(__GNUC__)
+    #define __restrict
+#endif
+
+// TODO: Not emitted with cbindgen
+#if __STDC_VERSION__ >= 199901L || defined(__cplusplus)
+    #define __inline inline
+#elif !defined(__GNUC__)
+    #define __inline
+#endif
+
+// Analogous to Rust's Never type
+//TODO: clang fails to compile C with [[noreturn]]
+#if defined(__cplusplus) && __HAS_ATTRIBUTE(noreturn) && !(__clang__)
+    #define __noreturn [[noreturn]]
+// #elif __STDC_VERSION__ >= 201112L
+// FIXME: cbindgen incorrectly places _Noreturn
+// #define __noreturn _Noreturn
+#elif defined(__GNUC__)
+    #define __noreturn __attribute__((__noreturn__))
+#else
+    #define __noreturn
+#endif
+
+// Analogous to Rust's #[must_use]
+// C23 only
+#if __HAS_ATTRIBUTE(nodiscard)
+    #define __nodiscard [[nodiscard]]
+    #define __nodiscardNote(x) [[nodiscard(x)]]
+#else
+    #define __nodiscard
+    #define __nodiscardNote(x)
+#endif
+
+// Analogous to Rust's #[deprecated]
+// C23 only
+#if __HAS_ATTRIBUTE(deprecated)
+    #define __deprecated [[deprecated]]
+    #define __deprecatedNote(x) [[deprecated(x)]]
+#else
+    #define __deprecated
+    #define __deprecatedNote(x)
 #endif
 
 #endif