=head1 NAME

Devel::CallChecker - custom op checking attached to subroutines

=head1 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);

=head1 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 C<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 C<cv_set_call_checker> and several

supporting functions available.  (It is possible to achieve the effect

of C<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, L</callchecker0_h> and L</callchecker_linkable>

should be called at build time (not authoring time) for the module that

wishes to use the C functions.

=cut

package Devel::CallChecker;

{ use 5.006; }

use warnings;

use strict;

our $VERSION = "0.008";

use parent "Exporter";

our @EXPORT_OK = qw(callchecker0_h callchecker_linkable);

{

	require DynaLoader;

	local our @ISA = qw(DynaLoader);

	local *dl_load_flags = sub { 1 };

	__PACKAGE__->bootstrap($VERSION);

}

=head1 CONSTANTS

=over

=item callchecker0_h

Content of a C header file, intended to be named "C<callchecker0.h>".

It is to be included in XS code, and C<perl.h> must be included first.

When the XS module is loaded at runtime, the C<Devel::CallChecker>

module must be loaded first.  This will result in the Perl API functions

C<rv2cv_op_cv>, C<ck_entersub_args_list>, C<ck_entersub_args_proto>,

C<ck_entersub_args_proto_or_list>, C<cv_get_call_checker>, and

C<cv_set_call_checker>, as defined below and in the Perl 5.14.0 API,

being available to the XS code.

=item 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.

=cut

sub callchecker_linkable() {

	require DynaLoader::Functions;

	DynaLoader::Functions->VERSION(0.001);

	return DynaLoader::Functions::linkable_for_module(__PACKAGE__);

}

=back

=head1 C FUNCTIONS

=over

=item 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.  I<cvop> is the op

being considered, normally an C<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 C<rv2cv> is to operate

on is provided by a suitable C<gv> or C<const> op.  Prior to 5.11.2,

only a C<gv> op will do.  A C<gv> op is suitable if the GV's CV slot

is populated.  A C<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 C<rv2cv> op has the C<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 I<flags> has the bit C<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 C<gv> op has the C<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 I<flags> has the bit C<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 C<CvGV> of the subroutine, but for an anonymous

(C<CvANON>) subroutine that is referenced through a GV it will be the

referencing GV.  The resulting C<GV*> is cast to C<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)

=item cv_get_call_checker

Retrieves the function that will be used to fix up a call to I<cv>.

Specifically, the function is applied to an C<entersub> op tree for a

subroutine call, not marked with C<&>, where the callee can be identified

at compile time as I<cv>.

The C-level function pointer is returned in I<*ckfun_p>, and an SV

argument for it is returned in I<*ckobj_p>.  The function is intended

to be called in this manner:

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

In this call, I<entersubop> is a pointer to the C<entersub> op,

which may be replaced by the check function, and I<namegv> is a GV

supplying the name that should be used by the check function to refer

to the callee of the C<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

L<Perl_ck_entersub_args_proto_or_list|/ck_entersub_args_proto_or_list>,

and the SV parameter is I<cv> itself.  This implements standard

prototype processing.  It can be changed, for a particular subroutine,

by L</cv_set_call_checker>.

    void cv_get_call_checker(CV *cv, Perl_call_checker *ckfun_p,

	    SV **ckobj_p)

=item cv_set_call_checker

Sets the function that will be used to fix up a call to I<cv>.

Specifically, the function is applied to an C<entersub> op tree for a

subroutine call, not marked with C<&>, where the callee can be identified

at compile time as I<cv>.

The C-level function pointer is supplied in I<ckfun>, and an SV argument

for it is supplied in I<ckobj>.  The function is intended to be called

in this manner:

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

In this call, I<entersubop> is a pointer to the C<entersub> op,

which may be replaced by the check function, and I<namegv> is a GV

supplying the name that should be used by the check function to refer

to the callee of the C<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

L</cv_get_call_checker>.

    void cv_set_call_checker(CV *cv, Perl_call_checker ckfun,

	    SV *ckobj)

=item ck_entersub_args_list

Performs the default fixup of the arguments part of an C<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 C<&>, 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)

=item ck_entersub_args_proto

Performs the fixup of the arguments part of an C<entersub> op tree

based on a subroutine prototype.  This makes various modifications to

the argument ops, from applying context up to inserting C<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 C<&>, where the callee can be identified at compile time

and has a prototype.

I<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 C<CV*>

that has been cast to C<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 I<namegv> parameter.

    OP *ck_entersub_args_proto(OP *entersubop, GV *namegv,

	    SV *protosv)

=item ck_entersub_args_proto_or_list

Performs the fixup of the arguments part of an C<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 C<&>, where the callee can be identified at compile time.

I<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 C<CV*>

that has been cast to C<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 I<namegv> parameter.

    OP *ck_entersub_args_proto_or_list(OP *entersubop, GV *namegv,

	    SV *protosv)

=back

=head1 SEE ALSO

L<B::CallChecker>,

L<Devel::CallParser>,

L<perlapi/cv_set_call_checker>

=head1 AUTHOR

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

=head1 COPYRIGHT

Copyright (C) 2011, 2012, 2013, 2015, 2017

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

=head1 LICENSE

This module is free software; you can redistribute it and/or modify it

under the same terms as Perl itself.

=cut

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