update ceph source to reef 18.1.2

[ceph.git] / ceph / src / boost / tools / build / src / build-system.jam

# Copyright 2003, 2005, 2007 Dave Abrahams
# Copyright 2006, 2007 Rene Rivera
# Copyright 2003, 2004, 2005, 2006 Vladimir Prus
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE.txt or copy at
# https://www.bfgroup.xyz/b2/LICENSE.txt)

# This file is part of Boost Build version 2. You can think of it as forming the
# main() routine. It is invoked by the bootstrapping code in bootstrap.jam.

import build-request ;
import builtin ;
import "class" : new ;
import configure ;
import config-cache ;
import feature ;
import generators ;
import indirect ;
import make ;
import modules ;
import os ;
import path ;
import project ;
import property ;
import property-set ;
import regex ;
import sequence ;
import targets ;
import toolset ;
import utility ;
import version ;
import virtual-target ;


################################################################################
#
# Module global data.
#
################################################################################

# Shortcut used in this module for accessing used command-line parameters.
.argv = [ modules.peek : ARGV ] ;

# Flag indicating we should display additional debugging information related to
# locating and loading Boost Build configuration files.
.debug-config = [ MATCH ^(--debug-configuration)$ : $(.argv) ] ;

# Virtual targets obtained when building main targets references on the command
# line. When running 'bjam --clean main_target' we want to clean only files
# belonging to that main target so we need to record which targets are produced
# for it.
.results-of-main-targets = ;

# Was an XML dump requested?
.out-xml = [ MATCH ^--out-xml=(.*)$ : $(.argv) ] ;

# Default toolset & version to be used in case no other toolset has been used
# explicitly by either the loaded configuration files, the loaded project build
# scripts or an explicit toolset request on the command line. If not specified,
# an arbitrary default will be used based on the current host OS. This value,
# while not strictly necessary, has been added to allow testing Boost-Build's
# default toolset usage functionality.
.default-toolset = ;
.default-toolset-version = ;


################################################################################
#
# Public rules.
#
################################################################################

# Returns the property set with the free features from the currently processed
# build request.
#
rule command-line-free-features ( )
{
    return $(.command-line-free-features) ;
}


# Returns the location of the build system. The primary use case is building
# Boost where it is sometimes needed to get the location of other components
# (e.g. BoostBook files) and it is convenient to use locations relative to the
# Boost Build path.
#
rule location ( )
{
    local r = [ modules.binding build-system ] ;
    return $(r:P) ;
}


# Sets the default toolset & version to be used in case no other toolset has
# been used explicitly by either the loaded configuration files, the loaded
# project build scripts or an explicit toolset request on the command line. For
# more detailed information see the comment related to used global variables.
#
rule set-default-toolset ( toolset : version ? )
{
    .default-toolset = $(toolset) ;
    .default-toolset-version = $(version) ;
}

rule add-pre-build-hook ( function )
{
    .pre-build-hook += [ indirect.make $(function) : [ CALLER_MODULE ] ] ;
}

rule add-post-build-hook ( function )
{
    .post-build-hook += [ indirect.make $(function) : [ CALLER_MODULE ] ] ;
}

# Old names for backwards compatibility
IMPORT build-system : add-pre-build-hook : build-system : set-pre-build-hook ;
IMPORT build-system : add-post-build-hook : build-system : set-post-build-hook ;
EXPORT build-system : set-pre-build-hook set-post-build-hook ;

################################################################################
#
# Local rules.
#
################################################################################

# Returns actual Jam targets to be used for executing a clean request.
#
local rule actual-clean-targets ( )
{
    # The cleaning is tricky. Say, if user says 'bjam --clean foo' where 'foo'
    # is a directory, then we want to clean targets which are in 'foo' as well
    # as those in any children Jamfiles under foo but not in any unrelated
    # Jamfiles. To achieve this we first mark all projects explicitly detected
    # as targets for this build system run as needing to be cleaned.
    for local t in $(targets)
    {
        if [ class.is-a $(t) : project-target ]
        {
            local project = [ $(t).project-module ] ;
            .should-clean-project.$(project) = true ;
        }
    }

    # Construct a list of targets explicitly detected on this build system run
    # as a result of building main targets.
    local targets-to-clean ;
    for local t in $(.results-of-main-targets)
    {
        # Do not include roots or sources.
        targets-to-clean += [ virtual-target.traverse $(t) ] ;
    }
    targets-to-clean = [ sequence.unique $(targets-to-clean) ] ;

    local to-clean ;
    for local t in [ virtual-target.all-targets ]
    {
        # Remove only derived targets and only those asked to be cleaned,
        # whether directly or by belonging to one of the removed projects.
        local p = [ $(t).project ] ;
        if [ $(t).action ] && ( $(t) in $(targets-to-clean) ||
            [ should-clean-project [ $(p).project-module ] ] )
        {
            to-clean += $(t) ;
        }
    }

    local to-clean-actual ;
    for local t in $(to-clean)
    {
        to-clean-actual += [ $(t).actualize ] ;
    }
    return $(to-clean-actual) ;
}


# Given a target id, try to find and return the corresponding target. This is
# only invoked when there is no Jamfile in ".". This code somewhat duplicates
# code in project-target.find but we can not reuse that code without a
# project-targets instance.
#
local rule find-target ( target-id )
{
    local split = [ MATCH (.*)//(.*) : $(target-id) ] ;

    local pm ;
    if $(split)
    {
        pm = [ project.find $(split[1]) : "." ] ;
    }
    else
    {
        pm = [ project.find $(target-id) : "." ] ;
    }

    local result ;
    if $(pm)
    {
        result = [ project.target $(pm) ] ;
    }

    if $(split)
    {
        result = [ $(result).find $(split[2]) ] ;
    }

    return $(result) ;
}


# Initializes a new configuration module.
#
local rule initialize-config-module ( module-name : location ? )
{
    project.initialize $(module-name) : $(location) ;
    if USER_MODULE in [ RULENAMES ]
    {
        USER_MODULE $(module-name) ;
    }
}


# Helper rule used to load configuration files. Loads the first configuration
# file with the given 'filename' at 'path' into module with name 'module-name'.
# Not finding the requested file may or may not be treated as an error depending
# on the must-find parameter. Returns a normalized path to the loaded
# configuration file or nothing if no file was loaded.
#
local rule load-config ( module-name : filename : path + : must-find ? )
{
    if $(.debug-config)
    {
        local path-string = $(path) ;
        if $(path-string) = "" { path-string = . ; }
        ECHO "notice:" Searching '$(path-string)' for $(module-name)
            configuration file '$(filename)'. ;
    }
    local where = [ GLOB $(path) : $(filename) ] ;
    if $(where)
    {
        where = [ NORMALIZE_PATH $(where[1]) ] ;
        if $(.debug-config)
        {
            local where-string = $(where:D) ;
            if $(where-string) = "" { where-string = . ; }
            where-string = '$(where-string)' ;
            ECHO "notice:" Loading $(module-name) configuration file '$(filename)'
                from $(where-string:J=" "). ;
        }

        # Set source location so that path-constant in config files with
        # relative paths work. This is of most importance for
        # project-config.jam, but may be used in other config files as well.
        local attributes = [ project.attributes $(module-name) ] ;
        $(attributes).set source-location : $(where:D) : exact ;
        modules.load $(module-name) : $(filename) : $(path) ;
        project.load-used-projects $(module-name) ;
    }
    else if $(must-find) || $(.debug-config)
    {
        local path-string = $(path) ;
        if $(path-string) = "" { path-string = . ; }
        path-string = '$(path-string)' ;
        path-string = $(path-string:J=" ") ;
        if $(must-find)
        {
            import errors ;
            errors.user-error Configuration file '$(filename)' not found "in"
                $(path-string). ;
        }
        ECHO "notice:" Configuration file '$(filename)' not found "in"
            $(path-string). ;
    }
    return $(where) ;
}

# Parses options of the form --xxx-config=path/to/config.jam
# and environmental variables of the form BOOST_BUILD_XXX_CONFIG.
# If not found, returns an empty list.  The option may be
# explicitly set to the empty string, in which case, handle-config-option
# will return "".
#
local rule handle-config-option ( name : env ? )
{
    local result = [ MATCH ^--$(name)=(.*)$ : $(.argv) ] ;
    if ! $(result)-is-defined && $(env)
    {
        result = [ os.environ $(env) ] ;
    }
    # Special handling for the case when the OS does not strip the quotes
    # around the file name, as is the case when using Cygwin bash.
    result = [ utility.unquote $(result[-1]) ] ;
    if ! $(result)
    {
        return $(result) ;
    }
    # Treat explicitly entered user paths as native OS path
    # references and, if non-absolute, root them at the current
    # working directory.
    result = [ path.make $(result) ] ;
    result = [ path.root $(result) [ path.pwd ] ] ;
    result = [ path.native $(result) ] ;
    return $(result) ;
}


# Loads all the configuration files used by Boost Build in the following order:
#
#   -- test-config --
#   Loaded only if specified on the command-line using the --test-config
# command-line parameter. It is ok for this file not to exist even if specified.
# If this configuration file is loaded, regular site and user configuration
# files will not be. If a relative path is specified, file is searched for in
# the current folder.
#
#   -- all-config --
#   Loaded only if specified on the command-line using the --config command
# line option.  If a file name is specified, it must exist and replaces all
# other configuration files.  If an empty file name is passed, no configuration
# files will be loaded.
#
#   -- site-config --
#   Named site-config.jam by default or may be named explicitly using the
# --site-config command-line option.  If named explicitly, the file is found
# relative to the current working directory and must exist.  If the default one
# is used then it is searched for in the system root path (Windows),
# /etc (non-Windows), user's home folder or the Boost Build path, in that
# order.  Not loaded in case the test-config configuration file is loaded,
# the file is explicitly set to the empty string or the --ignore-site-config
# command-line option is specified.
#
#   -- user-config --
#   Named user-config.jam by default or may be named explicitly using the
# --user-config command-line option or the BOOST_BUILD_USER_CONFIG environment
# variable. If named explicitly the file is looked for from the current working
# directory and if the default one is used then it is searched for in the
# user's home directory and the Boost Build path, in that order. Not loaded in
# case either the test-config configuration file is loaded or an empty file name
# is explicitly specified. If the file name has been given explicitly then the
# file must exist.
#
#   -- project-config --
#   Named project-config.jam. Looked up in the current working folder and
# then upwards through its parents up to the root folder.  It may also be
# named explicitly using the --project-config command-line option.  If a file
# is specified explicitly, it is found relative to the current working
# directory and must exist.  If an empty file name is passed, project-config
# will not be loaded.
#
# Test configurations have been added primarily for use by Boost Build's
# internal unit testing system but may be used freely in other places as well.
#
local rule load-configuration-files
{
    # Flag indicating that site configuration should not be loaded.
    local ignore-site-config =
        [ MATCH ^(--ignore-site-config)$ : $(.argv) ] ;
    local ignore-user-config ;
    local ignore-project-config ;

    initialize-config-module test-config ;
    local test-config = [ handle-config-option test-config ] ;
    if $(test-config)
    {
        local where = [ load-config test-config : $(test-config:BS) :
            $(test-config:D) ] ;
        if $(where)
        {
            if $(.debug-config)
            {
                ECHO "notice: Regular site and user configuration files will" ;
                ECHO "notice: be ignored due to the test configuration being"
                    "loaded." ;
            }
            ignore-site-config = true ;
            ignore-user-config = true ;
        }
    }

    initialize-config-module all-config ;
    local all-config = [ handle-config-option config ] ;
    if $(all-config)
    {
        load-config all-config : $(all-config:D=) : $(all-config:D) : required ;
        if $(.debug-config)
        {
            ECHO "notice: Regular configuration files will be ignored due" ;
            ECHO "notice: to the global configuration being loaded." ;
        }
    }
    if $(all-config)-is-defined
    {
        if $(.debug-config) && ! $(all-config)
        {
            ECHO "notice: Configuration file loading explicitly disabled." ;
        }
        ignore-site-config = true ;
        ignore-user-config = true ;
        ignore-project-config = true ;
    }

    local user-path = [ os.home-directories ] [ os.environ BOOST_BUILD_PATH ] ;
    local site-path = /etc $(user-path) ;
    if [ os.name ] in NT CYGWIN
    {
        site-path = [ modules.peek : SystemRoot ] $(user-path) ;
    }

    if $(.debug-config) && $(ignore-site-config) = --ignore-site-config
    {
        ECHO "notice: Site configuration files will be ignored due to the" ;
        ECHO "notice: --ignore-site-config command-line option." ;
    }

    initialize-config-module site-config ;
    if ! $(ignore-site-config)
    {
        local site-config = [ handle-config-option site-config ] ;
        if $(site-config)
        {
            load-config site-config : $(site-config:D=) : $(site-config:D)
                : must-exist ;
        }
        else if ! $(site-config)-is-defined
        {
            load-config site-config : site-config.jam : $(site-path) ;
        }
        else if $(.debug-config)
        {
            ECHO "notice:" Site configuration file loading explicitly disabled. ;
        }
    }

    initialize-config-module user-config ;
    if ! $(ignore-user-config)
    {
        local user-config =
            [ handle-config-option user-config : BOOST_BUILD_USER_CONFIG ] ;

        if $(user-config)
        {
            if $(.debug-config)
            {
                ECHO "notice:" Loading explicitly specified user configuration
                    "file:" ;
                ECHO "    $(user-config)" ;
            }

            load-config user-config : $(user-config:D=) : $(user-config:D)
                : must-exist ;
        }
        else if ! $(user-config)-is-defined
        {
            load-config user-config : user-config.jam : $(user-path) ;
        }
        else if $(.debug-config)
        {
            ECHO "notice:" User configuration file loading explicitly disabled. ;
        }
    }

    # We look for project-config.jam from "." upward. I am not sure this is 100%
    # right decision, we might as well check for it only alongside the Jamroot
    # file. However:
    # - We need to load project-config.jam before Jamroot
    # - We probably need to load project-config.jam even if there is no Jamroot
    #   - e.g. to implement automake-style out-of-tree builds.
    if ! $(ignore-project-config)
    {
        local project-config = [ handle-config-option project-config ] ;
        if $(project-config)
        {
            initialize-config-module project-config : $(project-config:D=) ;
            load-config project-config : $(project-config:D=)
                : $(project-config:D) : must-exist ;
        }
        else if ! $(project-config)-is-defined
        {
            local file = [ path.glob "." : project-config.jam ] ;
            if ! $(file)
            {
                file = [ path.glob-in-parents "." : project-config.jam ] ;
            }
            if $(file)
            {
                initialize-config-module project-config : $(file:D) ;
                load-config project-config : project-config.jam : $(file:D) ;
            }
        }
        else if $(.debug-config)
        {
            ECHO "notice:" Project configuration file loading explicitly
                disabled. ;
        }
    }

    project.end-load ;
}


# Autoconfigure toolsets based on any instances of --toolset=xx,yy,...zz or
# toolset=xx,yy,...zz in the command line. May return additional properties to
# be processed as if they had been specified by the user.
#
local rule process-explicit-toolset-requests
{
    local extra-properties ;

    local option-toolsets  = [ regex.split-list [ MATCH ^--toolset=(.*)$ : $(.argv) ] : "," ] ;
    local feature-toolsets = [ regex.split-list [ MATCH   ^toolset=(.*)$ : $(.argv) ] : "," ] ;

    for local t in $(option-toolsets) $(feature-toolsets)
    {
        # Parse toolset-version/properties.
        local toolset = [ MATCH "([^/]+)/?.*" : $(t) ] ;
        local properties = [ feature.expand-subfeatures <toolset>$(toolset) : true ] ;
        local toolset-property = [ property.select <toolset> : $(properties) ] ;
        local known ;
        if $(toolset-property:G=) in [ feature.values <toolset> ]
        {
            known = true ;
        }

        # If the toolset is not known, configure it now.

        # TODO: we should do 'using $(toolset)' in case no version has been
        # specified and there are no versions defined for the given toolset to
        # allow the toolset to configure its default version. For this we need
        # to know how to detect whether a given toolset has any versions
        # defined. An alternative would be to do this whenever version is not
        # specified but that would require that toolsets correctly handle the
        # case when their default version is configured multiple times which
        # should be checked for all existing toolsets first.

        if ! $(known)
        {
            if $(.debug-config)
            {
                ECHO "notice: [cmdline-cfg] toolset $(toolset) not"
                    "previously configured; attempting to auto-configure now" ;
            }
            local t,v = [ MATCH "([^-]+)-?(.+)?" : $(toolset) ] ;
            project.push-current ;
            toolset.using $(t,v[1]) : $(t,v[2]) ;
            project.pop-current ;
        }

        # Make sure we get an appropriate property into the build request in
        # case toolset has been specified using the "--toolset=..." command-line
        # option form.
        if ! $(t) in $(.argv) $(feature-toolsets)
        {
            if $(.debug-config)
            {
                ECHO "notice:" "[cmdline-cfg]" adding toolset=$(t) to the build
                    request. ;
            }
            extra-properties += toolset=$(t) ;
        }
    }

    return $(extra-properties) ;
}


# Returns whether the given project (identifed by its project module) should be
# cleaned because it or any of its parent projects have already been marked as
# needing to be cleaned in this build. As an optimization, will explicitly mark
# all encountered project needing to be cleaned in case thay have not already
# been marked so.
#
local rule should-clean-project ( project )
{
    if ! $(.should-clean-project.$(project))-is-defined
    {
        local r = "" ;
        if ! [ project.is-jamroot-module $(project) ]
        {
            local parent = [ project.attribute $(project) parent-module ] ;
            if $(parent)
            {
                r = [ should-clean-project $(parent) ] ;
            }
        }
        .should-clean-project.$(project) = $(r) ;
    }

    return $(.should-clean-project.$(project)) ;
}


################################################################################
#
# main()
# ------
#
################################################################################

{
    if --version in $(.argv)
    {
        version.print ;
        EXIT ;
    }

    version.verify-engine-version ;

    load-configuration-files ;

    # Load explicitly specified toolset modules.
    local extra-properties = [ process-explicit-toolset-requests ] ;

    # Load the actual project build script modules. We always load the project
    # in the current folder so 'use-project' directives have any chance of being
    # seen. Otherwise, we would not be able to refer to subprojects using target
    # ids.
    local current-project ;
    {
        local current-module = [ project.find "." : "." ] ;
        if $(current-module)
        {
            current-project = [ project.target $(current-module) ] ;
        }
    }

    # Load the default toolset module if no other has already been specified.
    if ! [ feature.values <toolset> ]
    {
        local default-toolset = $(.default-toolset) ;
        local default-toolset-version = ;
        if $(default-toolset)
        {
            default-toolset-version = $(.default-toolset-version) ;
        }
        else
        {
            default-toolset = gcc ;
            if [ os.name ] = NT
            {
                default-toolset = msvc ;
            }
            else if [ os.name ] = VMS
            {
                default-toolset = vmsdecc ;
            }
            else if [ os.name ] = MACOSX
            {
                default-toolset = clang ;
            }
        }

        ECHO "warning: No toolsets are configured." ;
        ECHO "warning: Configuring default toolset" \"$(default-toolset)\". ;
        ECHO "warning: If the default is wrong, your build may not work correctly." ;
        ECHO "warning: Use the \"toolset=xxxxx\" option to override our guess." ;
        ECHO "warning: For more configuration options, please consult" ;
        ECHO "warning: https://www.bfgroup.xyz/b2/manual/release/index.html#bbv2.overview.configuration" ;

        toolset.using $(default-toolset) : $(default-toolset-version) ;
    }


    # Parse command line for targets and properties. Note that this requires
    # that all project files already be loaded.
    # FIXME: This is not entirely true. Additional project files may be loaded
    # only later via the project.find() rule when dereferencing encountered
    # target ids containing explicit project references. See what to do about
    # those as such 'lazy loading' may cause problems that are then extremely
    # difficult to debug.
    local build-request = [ build-request.from-command-line $(.argv)
        $(extra-properties) ] ;
    local target-ids = [ $(build-request).get-at 1 ] ;
    local properties = [ $(build-request).get-at 2 ] ;


    # Check that we actually found something to build.
    if ! $(current-project) && ! $(target-ids)
    {
        import errors ;
        errors.user-error no Jamfile "in" current directory found, and no target
            references specified. ;
    }


    # Flags indicating that this build system run has been started in order to
    # clean existing instead of create new targets. Note that these are not the
    # final flag values as they may get changed later on due to some special
    # targets being specified on the command line.
    local clean    ; if "--clean"     in $(.argv) { clean    = true ; }
    local cleanall ; if "--clean-all" in $(.argv) { cleanall = true ; }


    # List of explicitly requested files to build. Any target references read
    # from the command line parameter not recognized as one of the targets
    # defined in the loaded Jamfiles will be interpreted as an explicitly
    # requested file to build. If any such files are explicitly requested then
    # only those files and the targets they depend on will be built and they
    # will be searched for among targets that would have been built had there
    # been no explicitly requested files.
    local explicitly-requested-files


    # List of Boost Build meta-targets, virtual-targets and actual Jam targets
    # constructed in this build system run.
    local targets ;
    local virtual-targets ;
    local actual-targets ;


    # Process each target specified on the command-line and convert it into
    # internal Boost Build target objects. Detect special clean target. If no
    # main Boost Build targets were explicitly requested use the current project
    # as the target.
    for local id in $(target-ids)
    {
        if $(id) = clean
        {
            clean = true ;
        }
        else
        {
            local t ;
            if $(current-project)
            {
                t = [ $(current-project).find $(id) : no-error ] ;
            }
            else
            {
                t = [ find-target $(id) ] ;
            }

            if ! $(t)
            {
                ECHO "notice: could not find main target" $(id) ;
                ECHO "notice: assuming it is a name of file to create." ;
                explicitly-requested-files += $(id) ;
            }
            else
            {
                targets += $(t) ;
            }
        }
    }
    if ! $(targets)
    {
        targets += [ project.target [ project.module-name "." ] ] ;
    }

    if [ option.get dump-generators : : true ]
    {
        generators.dump ;
    }

    # We wish to put config.log in the build directory corresponding to Jamroot,
    # so that the location does not differ depending on the directory we run the
    # build from. The amount of indirection necessary here is scary.
    local first-project = [ $(targets[0]).project ] ;
    local first-project-root-location = [ $(first-project).get project-root ] ;
    local first-project-root-module = [ project.load
        $(first-project-root-location) ] ;
    local first-project-root = [ project.target $(first-project-root-module) ] ;
    local first-build-build-dir = [ $(first-project-root).build-dir ] ;
    configure.set-log-file $(first-build-build-dir)/config.log ;
    config-cache.load $(first-build-build-dir)/project-cache.jam ;

    # Expand properties specified on the command line into multiple property
    # sets consisting of all legal property combinations. Each expanded property
    # set will be used for a single build run. E.g. if multiple toolsets are
    # specified then requested targets will be built with each of them.
    # The expansion is being performed as late as possible so that the feature
    # validation is performed after all necessary modules (including project targets
    # on the command line) have been loaded.
    if $(properties)
    {
        local cli_properties = [ build-request.convert-command-line-elements $(properties) ] ;
        if $(cli_properties)
        {
            expanded += $(cli_properties) ;
            expanded = [ build-request.expand-no-defaults $(expanded) ] ;
            local xexpanded ;
            for local e in $(expanded)
            {
                xexpanded += [ property-set.create [ feature.split $(e) ] ] ;
            }
            expanded = $(xexpanded) ;
        }
        else
        {
            expanded = [ property-set.empty ] ;
        }
    }
    else
    {
        expanded = [ property-set.empty ] ;
    }

    # Now that we have a set of targets to build and a set of property sets to
    # build the targets with, we can start the main build process by using each
    # property set to generate virtual targets from all of our listed targets
    # and any of their dependants.
    for local p in $(expanded)
    {
        .command-line-free-features = [ property-set.create [ $(p).free ] ] ;
        for local t in $(targets)
        {
            local g = [ $(t).generate $(p) ] ;
            if ! [ class.is-a $(t) : project-target ]
            {
                .results-of-main-targets += $(g[2-]) ;
            }
            virtual-targets += $(g[2-]) ;
        }
    }


    # Convert collected virtual targets into actual raw Jam targets.
    for t in $(virtual-targets)
    {
        actual-targets += [ $(t).actualize ] ;
    }

    config-cache.save ;


    # If XML data output has been requested prepare additional rules and targets
    # so we can hook into Jam to collect build data while its building and have
    # it trigger the final XML report generation after all the planned targets
    # have been built.
    if $(.out-xml)
    {
        # Get a qualified virtual target name.
        rule full-target-name ( target )
        {
            local name = [ $(target).name ] ;
            local project = [ $(target).project ] ;
            local project-path = [ $(project).get location ] ;
            return $(project-path)//$(name) ;
        }

        # Generate an XML file containing build statistics for each constituent.
        #
        rule out-xml ( xml-file : constituents * )
        {
            # Prepare valid XML header and footer with some basic info.
            local nl = "
" ;
            local os        = [ modules.peek : OS OSPLAT JAMUNAME ] "" ;
            local timestamp = [ modules.peek : JAMDATE ] ;
            local cwd       = [ PWD ] ;
            local command   = $(.argv) ;
            local bb-version = [ version.boost-build ] ;
            .header on $(xml-file) =
                "<?xml version=\"1.0\" encoding=\"utf-8\"?>"
                "$(nl)<build format=\"1.0\" version=\"$(bb-version)\">"
                "$(nl)  <os name=\"$(os[1])\" platform=\"$(os[2])\"><![CDATA[$(os[3-]:J= )]]></os>"
                "$(nl)  <timestamp><![CDATA[$(timestamp)]]></timestamp>"
                "$(nl)  <directory><![CDATA[$(cwd)]]></directory>"
                "$(nl)  <command><![CDATA[\"$(command:J=\" \")\"]]></command>"
                ;
            .footer on $(xml-file) =
                "$(nl)</build>" ;

            # Generate the target dependency graph.
            .contents on $(xml-file) +=
                "$(nl)  <targets>" ;
            for local t in [ virtual-target.all-targets ]
            {
                local action = [ $(t).action ] ;
                if $(action)
                    # If a target has no action, it has no dependencies.
                {
                    local name = [ full-target-name $(t) ] ;
                    local sources = [ $(action).sources ] ;
                    local dependencies ;
                    for local s in $(sources)
                    {
                        dependencies += [ full-target-name $(s) ] ;
                    }

                    local path = [ $(t).path ] ;
                    local jam-target = [ $(t).actual-name ] ;

                    .contents on $(xml-file) +=
                        "$(nl)    <target>"
                        "$(nl)      <name><![CDATA[$(name)]]></name>"
                        "$(nl)      <dependencies>"
                        "$(nl)        <dependency><![CDATA[$(dependencies)]]></dependency>"
                        "$(nl)      </dependencies>"
                        "$(nl)      <path><![CDATA[$(path)]]></path>"
                        "$(nl)      <jam-target><![CDATA[$(jam-target)]]></jam-target>"
                        "$(nl)    </target>"
                        ;
                }
            }
            .contents on $(xml-file) +=
                "$(nl)  </targets>" ;

            # Build $(xml-file) after $(constituents). Do so even if a
            # constituent action fails and regenerate the xml on every bjam run.
            INCLUDES $(xml-file) : $(constituents) ;
            ALWAYS $(xml-file) ;
            __ACTION_RULE__ on $(xml-file) =
                build-system.out-xml.generate-action ;
            out-xml.generate $(xml-file) ;
        }

        # The actual build actions are here; if we did this work in the actions
        # clause we would have to form a valid command line containing the
        # result of @(...) below (the name of the XML file).
        #
        rule out-xml.generate-action ( args * : xml-file
            : command status start end user system : output ? )
        {
            local contents =
                [ on $(xml-file) return $(.header) $(.contents) $(.footer) ] ;
            local f = @($(xml-file):E=$(contents)) ;
        }

        # Nothing to do here; the *real* actions happen in
        # out-xml.generate-action.
        actions quietly out-xml.generate { }

        # Define the out-xml file target, which depends on all the targets so
        # that it runs the collection after the targets have run.
        out-xml $(.out-xml) : $(actual-targets) ;

        # Set up a global __ACTION_RULE__ that records all the available
        # statistics about each actual target in a variable "on" the --out-xml
        # target.
        #
        rule out-xml.collect ( xml-file : target : command status start end user
            system : output ? )
        {
            local nl = "
" ;
            # Open the action with some basic info.
            .contents on $(xml-file) +=
                "$(nl)  <action status=\"$(status)\" start=\"$(start)\" end=\"$(end)\" user=\"$(user)\" system=\"$(system)\">" ;

            # If we have an action object we can print out more detailed info.
            local action = [ on $(target) return $(.action) ] ;
            if $(action)
            {
                local action-name    = [ $(action).action-name ] ;
                local action-sources = [ $(action).sources     ] ;
                local action-props   = [ $(action).properties  ] ;

                # The qualified name of the action which we created the target.
                .contents on $(xml-file) +=
                    "$(nl)    <name><![CDATA[$(action-name)]]></name>" ;

                # The sources that made up the target.
                .contents on $(xml-file) +=
                    "$(nl)    <sources>" ;
                for local source in $(action-sources)
                {
                    local source-actual = [ $(source).actual-name ] ;
                    .contents on $(xml-file) +=
                        "$(nl)      <source><![CDATA[$(source-actual)]]></source>" ;
                }
                .contents on $(xml-file) +=
                    "$(nl)    </sources>" ;

                # The properties that define the conditions under which the
                # target was built.
                .contents on $(xml-file) +=
                    "$(nl)    <properties>" ;
                for local prop in [ $(action-props).raw ]
                {
                    local prop-name = [ MATCH ^<(.*)>$ : $(prop:G) ] ;
                    .contents on $(xml-file) +=
                        "$(nl)      <property name=\"$(prop-name)\"><![CDATA[$(prop:G=)]]></property>" ;
                }
                .contents on $(xml-file) +=
                    "$(nl)    </properties>" ;
            }

            local locate = [ on $(target) return $(LOCATE) ] ;
            locate ?= "" ;
            .contents on $(xml-file) +=
                "$(nl)    <jam-target><![CDATA[$(target)]]></jam-target>"
                "$(nl)    <path><![CDATA[$(target:G=:R=$(locate))]]></path>"
                "$(nl)    <command><![CDATA[$(command)]]></command>"
                "$(nl)    <output><![CDATA[$(output)]]></output>" ;
            .contents on $(xml-file) +=
                "$(nl)  </action>" ;
        }

        # When no __ACTION_RULE__ is set "on" a target, the search falls back to
        # the global module.
        module
        {
            __ACTION_RULE__ = build-system.out-xml.collect
                [ modules.peek build-system : .out-xml ] ;
        }

        IMPORT
            build-system :
            out-xml.collect
            out-xml.generate-action
            : :
            build-system.out-xml.collect
            build-system.out-xml.generate-action
            ;
    }

    local j = [ option.get jobs ] ;
    if $(j)
    {
        modules.poke : PARALLELISM : $(j) ;
    }

    local k = [ option.get keep-going : true : true ] ;
    if $(k) in "on" "yes" "true"
    {
        modules.poke : KEEP_GOING : 1 ;
    }
    else if $(k) in "off" "no" "false"
    {
        modules.poke : KEEP_GOING : 0 ;
    }
    else
    {
        EXIT "error: Invalid value for the --keep-going option" ;
    }

    # The 'all' pseudo target is not strictly needed expect in the case when we
    # use it below but people often assume they always have this target
    # available and do not declare it themselves before use which may cause
    # build failures with an error message about not being able to build the
    # 'all' target.
    NOTFILE all ;

    # And now that all the actual raw Jam targets and all the dependencies
    # between them have been prepared all that is left is to tell Jam to update
    # those targets.
    if $(explicitly-requested-files)
    {
        # Note that this case can not be joined with the regular one when only
        # exact Boost Build targets are requested as here we do not build those
        # requested targets but only use them to construct the dependency tree
        # needed to build the explicitly requested files.
        UPDATE $(explicitly-requested-files:G=e) $(.out-xml) ;
    }
    else if $(cleanall)
    {
        UPDATE clean-all ;
    }
    else if $(clean)
    {
        common.Clean clean : [ actual-clean-targets ] ;
        UPDATE clean ;
    }
    else
    {
        configure.print-configure-checks-summary ;

        for local function in $(.pre-build-hook)
        {
            indirect.call $(function) ;
        }

        DEPENDS all : $(actual-targets) ;
        if UPDATE_NOW in [ RULENAMES ]
        {
            local ok = [ UPDATE_NOW all ] ;
            # Force sequence updating of regular targets, then the xml
            # log output target. To ensure the output records all built
            # as otherwise if could execute out-of-sequence when
            # doing parallel builds.
            if $(.out-xml)
            {
                UPDATE_NOW $(.out-xml) : : ignore-minus-n ;
            }
            for local function in $(.post-build-hook)
            {
                indirect.call $(function) $(ok) ;
            }
            # Prevent automatic update of the 'all' target, now that we have
            # explicitly updated what we wanted.
            UPDATE ;
        }
        else
        {
            UPDATE all $(.out-xml) ;
        }
    }
}