NAME

       Devel::CallChecker - custom op checking attached to subroutines

SYNOPSIS

           # to generate header prior to XS compilation

           perl -MDevel::CallChecker=callchecker0_h \
               -e 'print callchecker0_h' > callchecker0.h

           # in Perl part of module

           use Devel::CallChecker;

           /* in XS */

           #include "callchecker0.h"

           cv_get_call_checker(cv, &ckfun, &ckobj);
           static OP *my_ckfun(pTHX_ OP *o, GV *namegv, SV *ckobj);
           cv_set_call_checker(cv, my_ckfun, ckobj);

DESCRIPTION

       This module makes some new features of the Perl 5.14.0 C API available to XS modules running on older
       versions of Perl.  The features are centred around the function "cv_set_call_checker", which allows XS
       code to attach a magical annotation to a Perl subroutine, resulting in resolvable calls to that
       subroutine being mutated at compile time by arbitrary C code.  This module makes "cv_set_call_checker"
       and several supporting functions available.  (It is possible to achieve the effect of
       "cv_set_call_checker" from XS code on much earlier Perl versions, but it is painful to achieve without
       the centralised facility.)

       This module provides the implementation of the functions at runtime (on Perls where they are not provided
       by the core).  It also, at compile time, supplies the C header file and link library which provide access
       to the functions.  In normal use, "callchecker0_h" and "callchecker_linkable" should be called at build
       time (not authoring time) for the module that wishes to use the C functions.

CONSTANTS

       callchecker0_h
           Content of a C header file, intended to be named ""callchecker0.h"".  It is to be included in XS
           code, and "perl.h" must be included first.  When the XS module is loaded at runtime, the
           "Devel::CallChecker" module must be loaded first.  This will result in the Perl API functions
           "rv2cv_op_cv", "ck_entersub_args_list", "ck_entersub_args_proto", "ck_entersub_args_proto_or_list",
           "cv_get_call_checker", and "cv_set_call_checker", as defined below and in the Perl 5.14.0 API, being
           available to the XS code.

       callchecker_linkable
           List of names of files that must be used as additional objects when linking an XS module that uses
           the C functions supplied by this module.  This list will be empty on many platforms.

C FUNCTIONS

       rv2cv_op_cv
           Examines an op, which is expected to identify a subroutine at runtime, and attempts to determine at
           compile time which subroutine it identifies.  This is normally used during Perl compilation to
           determine whether a prototype can be applied to a function call.  cvop is the op being considered,
           normally an "rv2cv" op.  A pointer to the identified subroutine is returned, if it could be
           determined statically, and a null pointer is returned if it was not possible to determine statically.

           Whether the subroutine is statically identifiable is determined in accordance with the prevailing
           standards of the Perl version being used.  The same criteria are used that the core uses to determine
           whether to apply a prototype to a subroutine call.  From version 5.11.2 onwards, the subroutine can
           be determined if the RV that the "rv2cv" is to operate on is provided by a suitable "gv" or "const"
           op.  Prior to 5.11.2, only a "gv" op will do.  A "gv" op is suitable if the GV's CV slot is
           populated.  A "const" op is suitable if the constant value must be an RV pointing to a CV.  Details
           of this process may change in future versions of Perl.

           If the "rv2cv" op has the "OPpENTERSUB_AMPER" flag set then no attempt is made to identify the
           subroutine statically: this flag is used to suppress compile-time magic on a subroutine call, forcing
           it to use default runtime behaviour.

           If flags has the bit "RV2CVOPCV_MARK_EARLY" set, then the handling of a GV reference is modified.  If
           a GV was examined and its CV slot was found to be empty, then the "gv" op has the "OPpEARLY_CV" flag
           set.  If the op is not optimised away, and the CV slot is later populated with a subroutine having a
           prototype, that flag eventually triggers the warning "called too early to check prototype".

           If flags has the bit "RV2CVOPCV_RETURN_NAME_GV" set, then instead of returning a pointer to the
           subroutine it returns a pointer to the GV giving the most appropriate name for the subroutine in this
           context.  Normally this is just the "CvGV" of the subroutine, but for an anonymous ("CvANON")
           subroutine that is referenced through a GV it will be the referencing GV.  The resulting "GV*" is
           cast to "CV*" to be returned.  A null pointer is returned as usual if there is no statically-
           determinable subroutine.

               CV *rv2cv_op_cv(OP *cvop, U32 flags)

       cv_get_call_checker
           Retrieves the function that will be used to fix up a call to cv.  Specifically, the function is
           applied to an "entersub" op tree for a subroutine call, not marked with "&", where the callee can be
           identified at compile time as cv.

           The C-level function pointer is returned in *ckfun_p, and an SV argument for it is returned in
           *ckobj_p.  The function is intended to be called in this manner:

               entersubop = (*ckfun_p)(aTHX_ entersubop, namegv, (*ckobj_p));

           In this call, entersubop is a pointer to the "entersub" op, which may be replaced by the check
           function, and namegv is a GV supplying the name that should be used by the check function to refer to
           the callee of the "entersub" op if it needs to emit any diagnostics.  It is permitted to apply the
           check function in non-standard situations, such as to a call to a different subroutine or to a method
           call.

           By default, the function is Perl_ck_entersub_args_proto_or_list, and the SV parameter is cv itself.
           This implements standard prototype processing.  It can be changed, for a particular subroutine, by
           "cv_set_call_checker".

               void cv_get_call_checker(CV *cv, Perl_call_checker *ckfun_p,
                       SV **ckobj_p)

       cv_set_call_checker
           Sets the function that will be used to fix up a call to cv.  Specifically, the function is applied to
           an "entersub" op tree for a subroutine call, not marked with "&", where the callee can be identified
           at compile time as cv.

           The C-level function pointer is supplied in ckfun, and an SV argument for it is supplied in ckobj.
           The function is intended to be called in this manner:

               entersubop = ckfun(aTHX_ entersubop, namegv, ckobj);

           In this call, entersubop is a pointer to the "entersub" op, which may be replaced by the check
           function, and namegv is a GV supplying the name that should be used by the check function to refer to
           the callee of the "entersub" op if it needs to emit any diagnostics.  It is permitted to apply the
           check function in non-standard situations, such as to a call to a different subroutine or to a method
           call.

           The current setting for a particular CV can be retrieved by "cv_get_call_checker".

               void cv_set_call_checker(CV *cv, Perl_call_checker ckfun,
                       SV *ckobj)

       ck_entersub_args_list
           Performs the default fixup of the arguments part of an "entersub" op tree.  This consists of applying
           list context to each of the argument ops.  This is the standard treatment used on a call marked with
           "&", or a method call, or a call through a subroutine reference, or any other call where the callee
           can't be identified at compile time, or a call where the callee has no prototype.

               OP *ck_entersub_args_list(OP *entersubop)

       ck_entersub_args_proto
           Performs the fixup of the arguments part of an "entersub" op tree based on a subroutine prototype.
           This makes various modifications to the argument ops, from applying context up to inserting "refgen"
           ops, and checking the number and syntactic types of arguments, as directed by the prototype.  This is
           the standard treatment used on a subroutine call, not marked with "&", where the callee can be
           identified at compile time and has a prototype.

           protosv supplies the subroutine prototype to be applied to the call.  It may be a normal defined
           scalar, of which the string value will be used.  Alternatively, for convenience, it may be a
           subroutine object (a "CV*" that has been cast to "SV*") which has a prototype.  The prototype
           supplied, in whichever form, does not need to match the actual callee referenced by the op tree.

           If the argument ops disagree with the prototype, for example by having an unacceptable number of
           arguments, a valid op tree is returned anyway.  The error is reflected in the parser state, normally
           resulting in a single exception at the top level of parsing which covers all the compilation errors
           that occurred.  In the error message, the callee is referred to by the name defined by the namegv
           parameter.

               OP *ck_entersub_args_proto(OP *entersubop, GV *namegv,
                       SV *protosv)

       ck_entersub_args_proto_or_list
           Performs the fixup of the arguments part of an "entersub" op tree either based on a subroutine
           prototype or using default list-context processing.  This is the standard treatment used on a
           subroutine call, not marked with "&", where the callee can be identified at compile time.

           protosv supplies the subroutine prototype to be applied to the call, or indicates that there is no
           prototype.  It may be a normal scalar, in which case if it is defined then the string value will be
           used as a prototype, and if it is undefined then there is no prototype.  Alternatively, for
           convenience, it may be a subroutine object (a "CV*" that has been cast to "SV*"), of which the
           prototype will be used if it has one.  The prototype (or lack thereof) supplied, in whichever form,
           does not need to match the actual callee referenced by the op tree.

           If the argument ops disagree with the prototype, for example by having an unacceptable number of
           arguments, a valid op tree is returned anyway.  The error is reflected in the parser state, normally
           resulting in a single exception at the top level of parsing which covers all the compilation errors
           that occurred.  In the error message, the callee is referred to by the name defined by the namegv
           parameter.

               OP *ck_entersub_args_proto_or_list(OP *entersubop, GV *namegv,
                       SV *protosv)

SEE ALSO

       B::CallChecker, Devel::CallParser, "cv_set_call_checker" in perlapi

AUTHOR

       Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT

       Copyright (C) 2011, 2012, 2013, 2015, 2017 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.