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Editing: scan_args.h

#ifndef RBIMPL_SCAN_ARGS_H                           /*-*-C++-*-vi:se ft=cpp:*/
#define RBIMPL_SCAN_ARGS_H
/**
 * @file
 * @author     Ruby developers <ruby-core@ruby-lang.org>
 * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
 *             Permission  is hereby  granted,  to  either redistribute  and/or
 *             modify this file, provided that  the conditions mentioned in the
 *             file COPYING are met.  Consult the file for details.
 * @warning    Symbols   prefixed  with   either  `RBIMPL`   or  `rbimpl`   are
 *             implementation details.   Don't take  them as canon.  They could
 *             rapidly appear then vanish.  The name (path) of this header file
 *             is also an  implementation detail.  Do not expect  it to persist
 *             at the place it is now.  Developers are free to move it anywhere
 *             anytime at will.
 * @note       To  ruby-core:  remember  that   this  header  can  be  possibly
 *             recursively included  from extension  libraries written  in C++.
 *             Do not  expect for  instance `__VA_ARGS__` is  always available.
 *             We assume C99  for ruby itself but we don't  assume languages of
 *             extension libraries.  They could be written in C++98.
 * @brief      Compile-time static implementation of ::rb_scan_args().
 *
 * This  is a  beast.  It  statically analyses  the argument  spec string,  and
 * expands the assignment of variables into dedicated codes.
 */
#include "ruby/assert.h"
#include "ruby/internal/attr/diagnose_if.h"
#include "ruby/internal/attr/error.h"
#include "ruby/internal/attr/forceinline.h"
#include "ruby/internal/attr/nonnull.h"
#include "ruby/internal/attr/noreturn.h"
#include "ruby/internal/config.h"
#include "ruby/internal/dllexport.h"
#include "ruby/internal/has/attribute.h"
#include "ruby/internal/intern/array.h" /* rb_ary_new_from_values */
#include "ruby/internal/intern/error.h" /* rb_error_arity */
#include "ruby/internal/intern/hash.h"  /* rb_hash_dup */
#include "ruby/internal/intern/proc.h"  /* rb_block_proc */
#include "ruby/internal/iterator.h"     /* rb_block_given_p / rb_keyword_given_p */
#include "ruby/internal/static_assert.h"
#include "ruby/internal/stdbool.h"
#include "ruby/internal/value.h"

/**
 * @name Possible values that you should pass to rb_scan_args_kw().
 * @{
 */

/** Same behaviour as rb_scan_args(). */
#define RB_SCAN_ARGS_PASS_CALLED_KEYWORDS 0

/** The final argument should be a hash treated as keywords.*/
#define RB_SCAN_ARGS_KEYWORDS 1

/**
 * Treat a  final argument as  keywords if  it is a  hash, and not  as keywords
 * otherwise.
 */
#define RB_SCAN_ARGS_LAST_HASH_KEYWORDS 3

/** @} */

/**
 * @name Possible values that you should pass to rb_funcallv_kw().
 * @{
 */

/** Do not pass keywords. */
#define RB_NO_KEYWORDS 0

/** Pass keywords, final argument should be a hash of keywords. */
#define RB_PASS_KEYWORDS 1

/**
 * Pass keywords if current method is called with keywords, useful for argument
 * delegation
 */
#define RB_PASS_CALLED_KEYWORDS !!rb_keyword_given_p()

/** @} */

/**
 * @private
 *
 * @deprecated  This macro once was a thing in the old days, but makes no sense
 *              any  longer today.   Exists  here  for backwards  compatibility
 *              only.  You can safely forget about it.
 */
#define HAVE_RB_SCAN_ARGS_OPTIONAL_HASH 1

RBIMPL_SYMBOL_EXPORT_BEGIN()
RBIMPL_ATTR_NONNULL((2, 3))
/**
 * Retrieves argument from argc and  argv to given ::VALUE references according
 * to the format string.  The format can be described in ABNF as follows:
 *
 * ```
 * scan-arg-spec  := param-arg-spec [keyword-arg-spec] [block-arg-spec]
 *
 * param-arg-spec        := pre-arg-spec [post-arg-spec] / post-arg-spec /
 *                          pre-opt-post-arg-spec
 * pre-arg-spec          := num-of-leading-mandatory-args
 *                          [num-of-optional-args]
 * post-arg-spec         := sym-for-variable-length-args
 *                          [num-of-trailing-mandatory-args]
 * pre-opt-post-arg-spec := num-of-leading-mandatory-args num-of-optional-args
 *                          num-of-trailing-mandatory-args
 * keyword-arg-spec      := sym-for-keyword-arg
 * block-arg-spec        := sym-for-block-arg
 *
 * num-of-leading-mandatory-args  := DIGIT ; The number of leading mandatory
 *                                         ; arguments
 * num-of-optional-args           := DIGIT ; The number of optional arguments
 * sym-for-variable-length-args   := "*"   ; Indicates that variable length
 *                                         ;  arguments are captured as a ruby
 *                                         ; array
 * num-of-trailing-mandatory-args := DIGIT ; The number of trailing mandatory
 *                                         ; arguments
 * sym-for-keyword-arg            := ":"   ; Indicates that keyword argument
 *                                         ; captured as a hash.
 *                                         ; If keyword arguments are not
 *                                         ; provided, returns nil.
 * sym-for-block-arg              := "&"   ; Indicates that an iterator block
 *                                         ; should be captured if given
 * ```
 *
 * For example, "12" means that the  method requires at least one argument, and
 * at  most receives  three (1+2)  arguments.  So,  the format  string must  be
 * followed by three variable references, which  are to be assigned to captured
 * arguments.  For omitted arguments, variables are set to ::RUBY_Qnil.  `NULL`
 * can be put  in place of a variable reference,  which means the corresponding
 * captured argument(s) should be just dropped.
 *
 * The number of  given arguments, excluding an option hash  or iterator block,
 * is returned.
 *
 * @param[in]   argc          Length of `argv`.
 * @param[in]   argv          Pointer to the arguments to parse.
 * @param[in]   fmt           Format, in the language described above.
 * @param[out]  ...           Variables to fill in.
 * @exception   rb_eFatal     Malformed `fmt`.
 * @exception   rb_eArgError  Arity mismatch.
 * @return      Actually parsed number of given arguments.
 * @post        Each  values  passed to  `argv`  is  filled into  the  variadic
 *              arguments, according to the format.
 */
int rb_scan_args(int argc, const VALUE *argv, const char *fmt, ...);

RBIMPL_ATTR_NONNULL((3, 4))
/**
 * Identical to rb_scan_args(), except it also accepts `kw_splat`.
 *
 * @param[in]   kw_splat      How to understand the keyword arguments.
 *   - RB_SCAN_ARGS_PASS_CALLED_KEYWORDS: Same behaviour as rb_scan_args().
 *   - RB_SCAN_ARGS_KEYWORDS:             The final argument is a kwarg.
 *   - RB_SCAN_ARGS_LAST_HASH_KEYWORDS:   The final argument is a kwarg, iff it
 *                                        is a hash.
 * @param[in]   argc          Length of `argv`.
 * @param[in]   argv          Pointer to the arguments to parse.
 * @param[in]   fmt           Format, in the language described above.
 * @param[out]  ...           Variables to fill in.
 * @exception   rb_eFatal     Malformed `fmt`.
 * @exception   rb_eArgError  Arity mismatch.
 * @return      Actually parsed number of given arguments.
 * @post        Each  values  passed to  `argv`  is  filled into  the  variadic
 *              arguments, according to the format.
 */
int rb_scan_args_kw(int kw_splat, int argc, const VALUE *argv, const char *fmt, ...);

RBIMPL_ATTR_ERROR(("bad scan arg format"))
/**
 * @private
 *
 * This is  an implementation  detail of rb_scan_args().   People don't  use it
 * directly.
 */
void rb_scan_args_bad_format(const char*);

RBIMPL_ATTR_ERROR(("variable argument length doesn't match"))
/**
 * @private
 *
 * This is  an implementation  detail of rb_scan_args().   People don't  use it
 * directly.
 */
void rb_scan_args_length_mismatch(const char*,int);

RBIMPL_SYMBOL_EXPORT_END()

/** @cond INTERNAL_MACRO */

/* If we could use constexpr the following macros could be inline functions
 * ... but sadly we cannot. */

#define rb_scan_args_isdigit(c) (RBIMPL_CAST((unsigned char)((c)-'0'))<10)

#define rb_scan_args_count_end(fmt, ofs, vari) \
    ((fmt)[ofs] ? -1 : (vari))

#define rb_scan_args_count_block(fmt, ofs, vari) \
    ((fmt)[ofs]!='&' ? \
     rb_scan_args_count_end(fmt, ofs, vari) : \
     rb_scan_args_count_end(fmt, (ofs)+1, (vari)+1))

#define rb_scan_args_count_hash(fmt, ofs, vari) \
    ((fmt)[ofs]!=':' ? \
     rb_scan_args_count_block(fmt, ofs, vari) : \
     rb_scan_args_count_block(fmt, (ofs)+1, (vari)+1))

#define rb_scan_args_count_trail(fmt, ofs, vari) \
    (!rb_scan_args_isdigit((fmt)[ofs]) ? \
     rb_scan_args_count_hash(fmt, ofs, vari) : \
     rb_scan_args_count_hash(fmt, (ofs)+1, (vari)+((fmt)[ofs]-'0')))

#define rb_scan_args_count_var(fmt, ofs, vari) \
    ((fmt)[ofs]!='*' ? \
     rb_scan_args_count_trail(fmt, ofs, vari) : \
     rb_scan_args_count_trail(fmt, (ofs)+1, (vari)+1))

#define rb_scan_args_count_opt(fmt, ofs, vari) \
    (!rb_scan_args_isdigit((fmt)[ofs]) ? \
     rb_scan_args_count_var(fmt, ofs, vari) : \
     rb_scan_args_count_var(fmt, (ofs)+1, (vari)+(fmt)[ofs]-'0'))

#define rb_scan_args_count_lead(fmt, ofs, vari) \
    (!rb_scan_args_isdigit((fmt)[ofs]) ? \
     rb_scan_args_count_var(fmt, ofs, vari) : \
     rb_scan_args_count_opt(fmt, (ofs)+1, (vari)+(fmt)[ofs]-'0'))

#define rb_scan_args_count(fmt) rb_scan_args_count_lead(fmt, 0, 0)

#if RBIMPL_HAS_ATTRIBUTE(diagnose_if)
# /* Assertions done in the attribute. */
# define rb_scan_args_verify(fmt, varc) RBIMPL_ASSERT_NOTHING
#else
# /* At  one sight  it _seems_  the expressions  below could  be written  using
#  * static  assertions.  The  reality is  no, they  don't.  Because  fmt is  a
#  * string literal,  any operations  against fmt  cannot produce  the "integer
#  * constant  expression"s,  as  defined  in  ISO/IEC  9899:2018  section  6.6
#  * paragraph #6.  Static assertions need such integer constant expressions as
#  * defined in ISO/IEC 9899:2018 section 6.7.10 paragraph #3.
#  *
#  * GCC nonetheless constant-folds this into a no-op, though. */
# define rb_scan_args_verify(fmt, varc) \
    (sizeof(char[1-2*(rb_scan_args_count(fmt)<0)])!=1 ? \
     rb_scan_args_bad_format(fmt) : \
     sizeof(char[1-2*(rb_scan_args_count(fmt)!=(varc))])!=1 ? \
     rb_scan_args_length_mismatch(fmt, varc) : \
     RBIMPL_ASSERT_NOTHING)
#endif

static inline bool
rb_scan_args_keyword_p(int kw_flag, VALUE last)
{
    switch (kw_flag) {
      case RB_SCAN_ARGS_PASS_CALLED_KEYWORDS:
        return !! rb_keyword_given_p();
      case RB_SCAN_ARGS_KEYWORDS:
        return true;
      case RB_SCAN_ARGS_LAST_HASH_KEYWORDS:
        return RB_TYPE_P(last, T_HASH);
      default:
        return false;
    }
}

RBIMPL_ATTR_FORCEINLINE()
static bool
rb_scan_args_lead_p(const char *fmt)
{
    return rb_scan_args_isdigit(fmt[0]);
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_n_lead(const char *fmt)
{
    return (rb_scan_args_lead_p(fmt) ? fmt[0]-'0' : 0);
}

RBIMPL_ATTR_FORCEINLINE()
static bool
rb_scan_args_opt_p(const char *fmt)
{
    return (rb_scan_args_lead_p(fmt) && rb_scan_args_isdigit(fmt[1]));
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_n_opt(const char *fmt)
{
    return (rb_scan_args_opt_p(fmt) ? fmt[1]-'0' : 0);
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_var_idx(const char *fmt)
{
    return (!rb_scan_args_lead_p(fmt) ? 0 : !rb_scan_args_isdigit(fmt[1]) ? 1 : 2);
}

RBIMPL_ATTR_FORCEINLINE()
static bool
rb_scan_args_f_var(const char *fmt)
{
    return (fmt[rb_scan_args_var_idx(fmt)]=='*');
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_trail_idx(const char *fmt)
{
    const int idx = rb_scan_args_var_idx(fmt);
    return idx+(fmt[idx]=='*');
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_n_trail(const char *fmt)
{
    const int idx = rb_scan_args_trail_idx(fmt);
    return (rb_scan_args_isdigit(fmt[idx]) ? fmt[idx]-'0' : 0);
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_hash_idx(const char *fmt)
{
    const int idx = rb_scan_args_trail_idx(fmt);
    return idx+rb_scan_args_isdigit(fmt[idx]);
}

RBIMPL_ATTR_FORCEINLINE()
static bool
rb_scan_args_f_hash(const char *fmt)
{
    return (fmt[rb_scan_args_hash_idx(fmt)]==':');
}

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_block_idx(const char *fmt)
{
    const int idx = rb_scan_args_hash_idx(fmt);
    return idx+(fmt[idx]==':');
}

RBIMPL_ATTR_FORCEINLINE()
static bool
rb_scan_args_f_block(const char *fmt)
{
    return (fmt[rb_scan_args_block_idx(fmt)]=='&');
}

# if 0
RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_end_idx(const char *fmt)
{
    const int idx = rb_scan_args_block_idx(fmt);
    return idx+(fmt[idx]=='&');
}
# endif

/* NOTE: Use `char *fmt` instead of `const char *fmt` because of clang's bug*/
/* https://bugs.llvm.org/show_bug.cgi?id=38095 */
# define rb_scan_args0(argc, argv, fmt, varc, vars) \
    rb_scan_args_set(RB_SCAN_ARGS_PASS_CALLED_KEYWORDS, argc, argv, \
                     rb_scan_args_n_lead(fmt), \
                     rb_scan_args_n_opt(fmt), \
                     rb_scan_args_n_trail(fmt), \
                     rb_scan_args_f_var(fmt), \
                     rb_scan_args_f_hash(fmt), \
                     rb_scan_args_f_block(fmt), \
                     (rb_scan_args_verify(fmt, varc), vars), (char *)fmt, varc)
# define rb_scan_args_kw0(kw_flag, argc, argv, fmt, varc, vars) \
    rb_scan_args_set(kw_flag, argc, argv, \
                     rb_scan_args_n_lead(fmt), \
                     rb_scan_args_n_opt(fmt), \
                     rb_scan_args_n_trail(fmt), \
                     rb_scan_args_f_var(fmt), \
                     rb_scan_args_f_hash(fmt), \
                     rb_scan_args_f_block(fmt), \
                     (rb_scan_args_verify(fmt, varc), vars), (char *)fmt, varc)

RBIMPL_ATTR_FORCEINLINE()
static int
rb_scan_args_set(int kw_flag, int argc, const VALUE *argv,
                 int n_lead, int n_opt, int n_trail,
                 bool f_var, bool f_hash, bool f_block,
                 VALUE *vars[], RB_UNUSED_VAR(const char *fmt), RB_UNUSED_VAR(int varc))
    RBIMPL_ATTR_DIAGNOSE_IF(rb_scan_args_count(fmt) <  0,    "bad scan arg format",                    "error")
    RBIMPL_ATTR_DIAGNOSE_IF(rb_scan_args_count(fmt) != varc, "variable argument length doesn't match", "error")
{
    int i, argi = 0, vari = 0;
    VALUE *var, hash = Qnil;
#define rb_scan_args_next_param() vars[vari++]
    const int n_mand = n_lead + n_trail;

/* capture an option hash - phase 1: pop from the argv */
    if (f_hash && argc > 0) {
        VALUE last = argv[argc - 1];
        if (rb_scan_args_keyword_p(kw_flag, last)) {
            hash = rb_hash_dup(last);
            argc--;
        }
    }

if (argc < n_mand) {
        goto argc_error;
    }

/* capture leading mandatory arguments */
    for (i = 0; i < n_lead; i++) {
        var = rb_scan_args_next_param();
        if (var) *var = argv[argi];
        argi++;
    }

/* capture optional arguments */
    for (i = 0; i < n_opt; i++) {
        var = rb_scan_args_next_param();
        if (argi < argc - n_trail) {
            if (var) *var = argv[argi];
            argi++;
        }
        else {
            if (var) *var = Qnil;
        }
    }

/* capture variable length arguments */
    if (f_var) {
        int n_var = argc - argi - n_trail;

var = rb_scan_args_next_param();
        if (0 < n_var) {
            if (var) *var = rb_ary_new_from_values(n_var, &argv[argi]);
            argi += n_var;
        }
        else {
            if (var) *var = rb_ary_new();
        }
    }

/* capture trailing mandatory arguments */
    for (i = 0; i < n_trail; i++) {
        var = rb_scan_args_next_param();
        if (var) *var = argv[argi];
        argi++;
    }

/* capture an option hash - phase 2: assignment */
    if (f_hash) {
        var = rb_scan_args_next_param();
        if (var) *var = hash;
    }

/* capture iterator block */
    if (f_block) {
        var = rb_scan_args_next_param();
        if (rb_block_given_p()) {
            *var = rb_block_proc();
        }
        else {
            *var = Qnil;
        }
    }

if (argi == argc) {
        return argc;
    }

argc_error:
    rb_error_arity(argc, n_mand, f_var ? UNLIMITED_ARGUMENTS : n_mand + n_opt);
    UNREACHABLE_RETURN(-1);
#undef rb_scan_args_next_param
}

/** @endcond */

#if defined(__DOXYGEN__)
# /* don't bother */

#elif ! defined(HAVE_BUILTIN___BUILTIN_CHOOSE_EXPR_CONSTANT_P)
# /* skip */

#elif ! defined(HAVE_VA_ARGS_MACRO)
# /* skip */

#elif ! defined(__OPTIMIZE__)
# /* skip */

#elif defined(HAVE___VA_OPT__)
# define rb_scan_args(argc, argvp, fmt, ...)                  \
    __builtin_choose_expr(                                    \
        __builtin_constant_p(fmt),                            \
        rb_scan_args0(                                        \
            argc, argvp, fmt,                                 \
            (sizeof((VALUE*[]){__VA_ARGS__})/sizeof(VALUE*)), \
            ((VALUE*[]){__VA_ARGS__})),                       \
        (rb_scan_args)(argc, argvp, fmt __VA_OPT__(, __VA_ARGS__)))
# define rb_scan_args_kw(kw_flag, argc, argvp, fmt, ...)      \
    __builtin_choose_expr(                                    \
        __builtin_constant_p(fmt),                            \
        rb_scan_args_kw0(                                     \
            kw_flag, argc, argvp, fmt,                        \
            (sizeof((VALUE*[]){__VA_ARGS__})/sizeof(VALUE*)), \
            ((VALUE*[]){__VA_ARGS__})),                       \
        (rb_scan_args_kw)(kw_flag, argc, argvp, fmt __VA_OPT__(, __VA_ARGS__)))

#elif defined(__STRICT_ANSI__)
# /* skip */

#elif defined(__GNUC__)
# define rb_scan_args(argc, argvp, fmt, ...)                  \
    __builtin_choose_expr(                                    \
        __builtin_constant_p(fmt),                            \
        rb_scan_args0(                                        \
            argc, argvp, fmt,                                 \
            (sizeof((VALUE*[]){__VA_ARGS__})/sizeof(VALUE*)), \
            ((VALUE*[]){__VA_ARGS__})),                       \
        (rb_scan_args)(argc, argvp, fmt, __VA_ARGS__))
# define rb_scan_args_kw(kw_flag, argc, argvp, fmt, ...)      \
    __builtin_choose_expr(                                    \
        __builtin_constant_p(fmt),                            \
        rb_scan_args_kw0(                                     \
            kw_flag, argc, argvp, fmt,                        \
            (sizeof((VALUE*[]){__VA_ARGS__})/sizeof(VALUE*)), \
            ((VALUE*[]){__VA_ARGS__})),                       \
        (rb_scan_args_kw)(kw_flag, argc, argvp, fmt, __VA_ARGS__ /**/))
#endif

#endif /* RBIMPL_SCAN_ARGS_H */

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