neovim/src/nvim/assert.h

#ifndef NVIM_ASSERT_H
#define NVIM_ASSERT_H

#include "auto/config.h"

// support static asserts (aka compile-time asserts)

// some compilers don't properly support short-circuiting apparently, giving
// ugly syntax errors when using things like defined(__clang__) &&
// defined(__has_feature) && __has_feature(...). Therefore we define Clang's
// __has_feature and __has_extension macro's before referring to them.
#ifndef __has_feature
# define __has_feature(x) 0
#endif

#ifndef __has_extension
# define __has_extension __has_feature
#endif

/// @def STATIC_ASSERT
/// @brief Assert at compile time if condition is not satisfied.
///
/// Should be put on its own line, followed by a semicolon.
///
/// Example:
///
///     STATIC_ASSERT(sizeof(void *) == 8, "Expected 64-bit mode");
///
/// @param[in]  condition  Condition to check, should be an integer constant
///                        expression.
/// @param[in]  message  Message which will be given if check fails.

/// @def STATIC_ASSERT_EXPR
/// @brief Like #STATIC_ASSERT, but can be used where expressions are used.
///
/// STATIC_ASSERT_EXPR may be put in brace initializer lists. Error message
/// given in this case is not very nice with the current implementation though
/// and `message` argument is ignored.

// define STATIC_ASSERT as C11's _Static_assert whenever either C11 mode is
// detected or the compiler is known to support it. Note that Clang in C99
// mode defines __has_feature(c_static_assert) as false and
// __has_extension(c_static_assert) as true. Meaning it does support it, but
// warns. A similar thing goes for gcc, which warns when it's not compiling
// as C11 but does support _Static_assert since 4.6. Since we prefer the
// clearer messages we get from _Static_assert, we suppress the warnings
// temporarily.

#define STATIC_ASSERT_PRAGMA_START
#define STATIC_ASSERT_PRAGMA_END
#define STATIC_ASSERT(cond, msg) \
  do { \
    STATIC_ASSERT_PRAGMA_START \
    STATIC_ASSERT_STATEMENT(cond, msg); \
    STATIC_ASSERT_PRAGMA_END \
  } while (0)

// the easiest case, when the mode is C11 (generic compiler) or Clang
// advertises explicit support for c_static_assert, meaning it won't warn.
#if __STDC_VERSION__ >= 201112L || __has_feature(c_static_assert)
# define STATIC_ASSERT_STATEMENT(cond, msg) _Static_assert(cond, msg)
// if we're dealing with gcc >= 4.6 in C99 mode, we can still use
// _Static_assert but we need to suppress warnings, this is pretty ugly.
#elif (!defined(__clang__) && !defined(__INTEL_COMPILER)) &&  /* NOLINT(whitespace/parens)*/ \
  (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6))

# define STATIC_ASSERT_STATEMENT(cond, msg) _Static_assert(cond, msg)

# undef STATIC_ASSERT_PRAGMA_START

# if __GNUC__ >= 6
#  define STATIC_ASSERT_PRAGMA_START \
  _Pragma("GCC diagnostic push") \
  _Pragma("GCC diagnostic ignored \"-Wpedantic\"")
# else
#  define STATIC_ASSERT_PRAGMA_START \
  _Pragma("GCC diagnostic push") \
  _Pragma("GCC diagnostic ignored \"-pedantic\"")
# endif

# undef STATIC_ASSERT_PRAGMA_END
# define STATIC_ASSERT_PRAGMA_END \
  _Pragma("GCC diagnostic pop")

// the same goes for clang in C99 mode, but we suppress a different warning
#elif defined(__clang__) && __has_extension(c_static_assert)

# define STATIC_ASSERT_STATEMENT(cond, msg) _Static_assert(cond, msg)

# undef STATIC_ASSERT_PRAGMA_START
# define STATIC_ASSERT_PRAGMA_START \
  _Pragma("clang diagnostic push") \
  _Pragma("clang diagnostic ignored \"-Wc11-extensions\"")

# undef STATIC_ASSERT_PRAGMA_END
# define STATIC_ASSERT_PRAGMA_END \
  _Pragma("clang diagnostic pop")

// TODO(aktau): verify that this works, don't have MSVC on hand.
#elif _MSC_VER >= 1600

# define STATIC_ASSERT_STATEMENT(cond, msg) static_assert(cond, msg)

// fallback for compilers that don't support _Static_assert or static_assert
// not as pretty but gets the job done. Credit goes to Pádraig Brady and
// contributors.
#else
# define STATIC_ASSERT_STATEMENT STATIC_ASSERT_EXPR
#endif

#define ASSERT_CONCAT_(a, b) a##b
#define ASSERT_CONCAT(a, b) ASSERT_CONCAT_(a, b)
// These can't be used after statements in c89.
#ifdef __COUNTER__
# define STATIC_ASSERT_EXPR(e, m) \
  ((enum { ASSERT_CONCAT(static_assert_, __COUNTER__) = 1/(!!(e)), }) 0)
#else
// This can't be used twice on the same line so ensure if using in headers
// that the headers are not included twice (by wrapping in #ifndef...#endif)
// Note it doesn't cause an issue when used on same line of separate modules
// compiled with gcc -combine -fwhole-program.
# define STATIC_ASSERT_EXPR(e, m) \
  ((enum { ASSERT_CONCAT(assert_line_, __LINE__) = 1/(!!(e)), }) 0)
#endif

/// @def STRICT_ADD
/// @brief Adds (a + b) and stores result in `c`.  Aborts on overflow.
///
/// Requires GCC 5+ and Clang 3.8+
///   https://clang.llvm.org/docs/LanguageExtensions.html
///   https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html
///
/// Alternative for compilers without __builtin_xx_overflow ?
///   https://stackoverflow.com/a/44830670/152142
///
/// @param a  Operand 1.
/// @param b  Operand 2.
/// @param c  Where to store the result.
/// @param t  Result type. Not used if compiler supports __builtin_add_overflow.
#ifdef HAVE_BUILTIN_ADD_OVERFLOW
# define STRICT_ADD(a, b, c, t) \
  do { \
    if (__builtin_add_overflow(a, b, c)) { \
      ELOG("STRICT_ADD overflow"); \
      abort(); \
    } \
  } while (0)
#else
# define STRICT_ADD(a, b, c, t) \
  do { *(c) = (t)((a) + (b)); } while (0)
#endif

/// @def STRICT_SUB
/// @brief Subtracts (a - b) and stores result in `c`.  Aborts on overflow.
/// @see STRICT_ADD
#ifdef HAVE_BUILTIN_ADD_OVERFLOW
# define STRICT_SUB(a, b, c, t) \
  do { \
    if (__builtin_sub_overflow(a, b, c)) { \
      ELOG("STRICT_SUB overflow"); \
      abort(); \
    } \
  } while (0)
#else
# define STRICT_SUB(a, b, c, t) \
  do { *(c) = (t)((a) - (b)); } while (0)
#endif

#endif  // NVIM_ASSERT_H