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# Copyright 2017 Rene Rivera
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE_1_0.txt or copy at
# http://www.boost.org/LICENSE_1_0.txt)

# TODO: Documentation.

import feature ;
import errors ;
import property ;

feature.feature variant
    :
    : implicit composite propagated symmetric ;

# Declares a new variant.
#
# First determines explicit properties for this variant, by refining parents'
# explicit properties with the passed explicit properties. The result is
# remembered and will be used if this variant is used as parent.
#
# Second, determines the full property set for this variant by adding to the
# explicit properties default values for all missing non-symmetric properties.
#
# Lastly, makes appropriate value of 'variant' property expand to the full
# property set.
#
rule variant ( name            # Name of the variant
    : parents-or-properties *  # Specifies parent variants, if
                               # 'explicit-properties' are given, and
                               # explicit-properties or parents otherwise.
    : explicit-properties *    # Explicit properties.
    )
{
    local parents ;
    if ! $(explicit-properties)
    {
        if $(parents-or-properties[1]:G)
        {
            explicit-properties = $(parents-or-properties) ;
        }
        else
        {
            parents = $(parents-or-properties) ;
        }
    }
    else
    {
        parents = $(parents-or-properties) ;
    }

    # The problem is that we have to check for conflicts between base variants.
    if $(parents[2])
    {
        errors.error "multiple base variants are not yet supported" ;
    }

    local inherited ;
    # Add explicitly specified properties for parents.
    for local p in $(parents)
    {
        # TODO: This check may be made stricter.
        if ! [ feature.is-implicit-value $(p) ]
        {
            errors.error "Invalid base variant" $(p)  ;
        }

        inherited += $(.explicit-properties.$(p)) ;
    }
    property.validate $(explicit-properties) ;
    explicit-properties = [ property.refine $(inherited)
        : $(explicit-properties) ] ;

    # Record explicitly specified properties for this variant. We do this after
    # inheriting parents' properties so they affect other variants derived from
    # this one.
    .explicit-properties.$(name) = $(explicit-properties) ;

    feature.extend variant : $(name) ;
    feature.compose <variant>$(name) : $(explicit-properties) ;
}
IMPORT $(__name__) : variant : : variant ;