Kaleidoscope/src/macro_helpers.h

#pragma once

// Code generated by muli-line pre-processor macros is hard to read after
//    pre-processing.
//
// When you want to check pre-processed code, e.g. for debugging or
// to understand what's going on, do the following:
//
// 1) Add the compiler command line definition
//      -DKALEIDOSCOPE_ENABLE_MACRO_NEWLINE_SUBSTITUTION
//    This prevents the __NL__ macro being defined below.
// 2) Generate the preprocessed code (it will contain a lot of __NL__ definitions).
// 3) Open the pre-processed code in your favorite editor.
//    3.1) Replace all __NL__ with newline characters.
//       In vim the command would be ':%s/__NL__/\r/g'.
//    3.2) Autocorrect code-indenting to improve readability. This is necessary
//       as pre-processor macros remove all whitespaces at the beginning of lines.
//       With vim, the command gg=G helps (just type the characters one after
//       the other).
// 4) Don't forget to remove the
//       -DKALEIDOSCOPE_ENABLE_MACRO_NEWLINE_SUBSTITUTION
//    from your compiler command line. Else the code won't compile.

#ifndef KALEIDOSCOPE_ENABLE_MACRO_NEWLINE_SUBSTITUTION
#define __NL__
#endif

#define __NN__

// Some auxiliary macros
//
#define __STRINGIZE(S) #S
#define STRINGIZE(S) __STRINGIZE(S)

// Allow for the creation of verbose messages in static_asserts
//
#define VERBOSE_STATIC_ASSERT_HEADER                                           \
   "\n"                                                                 __NL__ \
   "\n***************************************************************"  __NL__ \
   "\n******************** READ THIS CAREFULLY! *********************"  __NL__ \
   "\n***************************************************************"  __NL__ \
   "\n"

#define VERBOSE_STATIC_ASSERT_FOOTER                                           \
   "\n"                                                                 __NL__ \
   "\n***************************************************************"  __NL__ \
   "\n***************************************************************"  __NL__ \
   "\n***************************************************************"  __NL__ \
   "\n"

#define VERBOSE_FILE_INFO                                                      \
   "\nFile: " __FILE__                                                  __NL__

#define VERBOSE_LINE_INFO                                                      \
   "\nLine: " STRINGIZE(__LINE__)                                       __NL__

// The macro function RESTRICT_ARGS_COUNT can be used to generate more
// verbose error messages when users supply an insuitable number of arguments
// to a macro.
//
// For a macro it is used wherever one of the arguments A, B, C might
// be used, e.g.
//
#if 0 // This is just so that A_MACRO is not actually defined
#define A_MACRO(A, B, C, ...) \
      (void)RESTRICT_ARGS_COUNT(0, 3, A_MACRO, ##__VA_ARGS__); \
      int a = A; \
      int b = B; \
      int c = C;
#endif
//
// Note that RESTRICT_ARGS_COUNT can also be invoked wherever one of the macro
// arguments is used, e.g.
//
#if 0 // This is just so that B_MACRO is not actually defined
#define B_MACRO(A, B, C, ...)
int array[] = { A, B, RESTRICT_ARGS_COUNT(C, 3, B_MACRO, ##__VA_ARGS__) };
#endif
//
#define RESTRICT_ARGS_COUNT(B,                                                 \
                            NUM_EXPECTED_ARGS,                                 \
                            ORIGINAL_MACRO,                                    \
                            ...)                                               \
   (                                                                        __NL__ \
   []{ /* Here we are in the body of a dummy lambda function.            */ __NL__ \
       /* []{} is, BTW, the shortest way to write a lambda.              */ __NL__ \
       /* It is only used to hold the static_assert that cannot be       */ __NL__ \
       /* defined directly in the keymap initializer list. By using the  */ __NL__ \
       /* comma operator ((A, B) always evaluates to b), we ensure       */ __NL__ \
       /* that not the lambda but B is what ASSERT_ARGS_COUNT            */ __NL__ \
       /* finally evaluates to.                                          */ __NL__ \
       /* Please not that passing B through this macro is a must         */ __NL__ \
       /* as we need it for the comma operator to work.                  */ __NL__ \
   static_assert(sizeof(const char) == sizeof(#__VA_ARGS__ ),               __NL__ \
        /* sizeof(const char) == sizeof(#__VA_ARGS__ ) checks the quoted */ __NL__ \
        /* list of additional arguments. If there are none, then the     */ __NL__ \
        /* length of #__VA_ARGS__ is a single char as it contains '\0'.  */ __NL__ \
        /* This check is not able to find the corner case of a single    */ __NL__ \
        /* superfluous comma at the end of the macro arguments as this   */ __NL__ \
        /* causes #__VA_ARGS__ being empty (only '\0').                  */ __NL__ \
     VERBOSE_STATIC_ASSERT_HEADER                                           __NL__ \
                                                                            __NL__ \
     VERBOSE_FILE_INFO                                                      __NL__ \
     VERBOSE_LINE_INFO                                                      __NL__ \
     "\n"                                                                   __NL__ \
     "\nStrange arguments found in invocation of " #ORIGINAL_MACRO "."      __NL__ \
     "\n"                                                                   __NL__ \
     "\nPlease make sure to pass exactly " #NUM_EXPECTED_ARGS               __NL__ \
                                          " macro arguments to"             __NL__ \
     "\n" #ORIGINAL_MACRO ". Also make sure that there are no dangling"     __NL__ \
     "\ncommas at the end of the argument list."                            __NL__ \
     "\n"                                                                   __NL__ \
     "\nThis is the superfluous part at the end of the macro"               __NL__ \
     "\narguments list: \'" #__VA_ARGS__ "\'"                               __NL__ \
                                                                            __NL__ \
     VERBOSE_STATIC_ASSERT_FOOTER                                           __NL__ \
   );                                                                       __NL__ \
                                                                            __NL__ \
   }, /* End of dummy lambda, the comma operator's A operand. */            __NL__ \
   B     /* The overall ASSERT_ARGS_COUNT evaluates to B. */                __NL__ \
   )