1. Composition

In this chapter we will explore how to create compositions of multiple input filesystem trees, using the compose element.

Note

This example is distributed with BuildStream in the doc/examples/composition subdirectory.

1.1. Overview

Composing a directory tree based on a set of build dependencies is often one of the important steps you might perform in order to create a single artifact which can be checked out and deployed.

In order to use the compose element, it is important to first understand the concept of split rules, which we will cover in this chapter.

1.1.1. Introducing split rules

The split rules of an element declaration denote which sets of files in the given element’s resulting artifact belong to which domain name.

The domains can then be used in various ways, using plugins which understand split rule domains.

BuildStream’s default project configuration contains a sensible set of default split rule domains for the purpose of artifact splitting, they can be overridden in your project.conf, and finally on a per element basis in the public data of your element declarations.

Note

Projects are free to add additional split rule domains on top of the default domains provided by the default project configuration.

There is nothing wrong with defining split rule domains which overlap, possibly capturing some of the same files also captured by another domain, however you should be aware of this when later using your split rules with a plugin which processes them, like the compose element described in this chapter.

1.1.1.1. Example of split rule declaration

In an element, you might need to define or extend the split-rules in order to capture files in custom locations in a logical domain.

Here is an example of how you might use the list append directive to append an additional rule to your split-rules list in order to capture additional data files which your application or library might want to include in the runtime domain:

# Add our .dat files to the runtime domain
public:
  bst:
    split-rules:
      runtime:
        (>):
        - |
          %{datadir}/foo/*.dat

Split rules are absolute paths which denote files within an artifact’s root directory. The globbing patterns supported in split rules are defined in the reference documentation here.

Important

Note that because of variable expansion, split rules can often be resolved differently for elements which have overridden path related variables, like %{prefix}.

This usually means that you do not need to explicitly extend or override split rules on a specific element unless your element installs files to special case locations.

1.2. Project structure

In this example we expand on the chapter about integration commands, so we will only discuss the files which are added or changed from that example.

1.2.1. elements/base/alpine.bst

kind: import
description: |

    Alpine Linux base runtime

sources:
- kind: tar
  url: alpine:integration-tests-base.v1.x86_64.tar.xz
  ref: 3eb559250ba82b64a68d86d0636a6b127aa5f6d25d3601a79f79214dc9703639

public:
  bst:
    #
    # Run ldconfig in the libdir before running anything
    #
    integration-commands:
    - ldconfig "%{libdir}"

    #
    # Extend the runtime split-rule domain for this element,
    # such that we capture the runtime linker.
    #
    # There are various other things provided by this runtime
    # such as tooling in /bin and an installation of python
    # and perl, but we'll overlook these for the sake of
    # this example.
    #
    split-rules:
      runtime:
        (>):
        - "/lib/ld*.so*"

Here we have modified the base runtime, so as to specify that for this element, we want to also include the runtime linker into the runtime domain.

1.2.2. elements/runtime-only.bst

kind: compose

# Dependencies of a compose element cannot be transient,
# we can only build-depend on the inputs of a composition.
#
build-depends:
- hello.bst

config:

  # Only include files from the runtime domain
  #
  include:
  - runtime

  # Don't include any files which do not match any existing
  # split rule domains.
  #
  include-orphans: False

  # Run integration commands before composition
  #
  integrate: True

As we can see, this compose element has been configured to only include files from the runtime domain.

1.3. Using the project

Now that we’ve presented how split rules work and shown how to use them in the context of this example, lets use the compose element we’ve created and observe the results.

1.3.1. Building the project

user@host:~/composition$ bst build runtime-only.bst

[--:--:--][        ][    main:core activity                 ] START   Build
[--:--:--][        ][    main:core activity                 ] START   Loading elements
[00:00:00][        ][    main:core activity                 ] SUCCESS Loading elements
[--:--:--][        ][    main:core activity                 ] START   Resolving elements
[00:00:00][        ][    main:core activity                 ] SUCCESS Resolving elements
[--:--:--][        ][    main:core activity                 ] START   Initializing remote caches
[00:00:00][        ][    main:core activity                 ] SUCCESS Initializing remote caches
[--:--:--][        ][    main:core activity                 ] START   Query cache
[00:00:00][        ][    main:core activity                 ] SUCCESS Query cache

BuildStream Version 2.2.1
    Session Start: Wednesday, 22-05-2024 at 09:43:49
    Project:       composition (/home/user/buildstream/doc/examples/composition)
    Targets:       runtime-only.bst

User Configuration
    Configuration File:      /home/user/buildstream/doc/run-bst-qtkopl8t/buildstream.conf
    Cache Directory:         /home/user/buildstream/doc/run-bst-qtkopl8t
    Log Files:               /home/user/buildstream/doc/run-bst-qtkopl8t/logs
    Source Mirrors:          /home/user/buildstream/doc/run-bst-qtkopl8t/sources
    Build Area:              /home/user/buildstream/doc/run-bst-qtkopl8t/build
    Strict Build Plan:       Yes
    Maximum Fetch Tasks:     10
    Maximum Build Tasks:     4
    Maximum Push Tasks:      4
    Maximum Network Retries: 2

Project: composition

    Element Plugins
        compose: core plugin
        manual:  core plugin
        stack:   core plugin
        import:  core plugin

    Source Plugins
        local: core plugin
        tar:   core plugin

Pipeline
fetch needed 2f643c2da05dd1f300aa1b5aa016a925a6fecfdb3c9ff947c66a97002496aac2 base/alpine.bst 
     waiting 82d7d3429a94cd01054753bbdc565d3f37069aacba51051764ec0f72129349f7 base.bst 
     waiting 0babd9cc5beb41704ffe9a110ed8b4ca69ff8241a630b46176052544c07a35b2 libhello.bst 
     waiting 6fb0f24a1fee36ba2f486fa0cd0cbedeb8f7a69df15908b9370aaa7799f8353d hello.bst 
     waiting c22b89ed1a1f72aac4ee28fe220f9efa2c2d4002a1b1c414e659cfb089435960 runtime-only.bst 
===============================================================================
[--:--:--][0babd9cc][   fetch:libhello.bst                  ] START   composition/libhello/0babd9cc-fetch.20240522-094349.log
[--:--:--][2f643c2d][   fetch:base/alpine.bst               ] START   composition/base-alpine/2f643c2d-fetch.20240522-094349.log
[--:--:--][82d7d342][   fetch:base.bst                      ] START   composition/base/82d7d342-fetch.20240522-094349.log
[--:--:--][2f643c2d][   fetch:base/alpine.bst               ] START   Fetching https://bst-integration-test-images.ams3.cdn.digitaloceanspaces.com/integration-tests-base.v1.x86_64.tar.xz
[--:--:--][c22b89ed][   fetch:runtime-only.bst              ] START   composition/runtime-only/c22b89ed-fetch.20240522-094349.log
[00:00:00][c22b89ed][   fetch:runtime-only.bst              ] SUCCESS composition/runtime-only/c22b89ed-fetch.20240522-094349.log
[00:00:00][0babd9cc][   fetch:libhello.bst                  ] SUCCESS composition/libhello/0babd9cc-fetch.20240522-094349.log
[00:00:00][82d7d342][   fetch:base.bst                      ] SUCCESS composition/base/82d7d342-fetch.20240522-094349.log
[00:00:00][2f643c2d][   fetch:base/alpine.bst               ] SUCCESS Fetching https://bst-integration-test-images.ams3.cdn.digitaloceanspaces.com/integration-tests-base.v1.x86_64.tar.xz
[00:00:05][2f643c2d][   fetch:base/alpine.bst               ] SUCCESS composition/base-alpine/2f643c2d-fetch.20240522-094349.log
[--:--:--][2f643c2d][   build:base/alpine.bst               ] START   composition/base-alpine/2f643c2d-build.20240522-094354.log
[--:--:--][2f643c2d][   build:base/alpine.bst               ] START   Staging sources
[00:00:00][2f643c2d][   build:base/alpine.bst               ] SUCCESS Staging sources
[--:--:--][2f643c2d][   build:base/alpine.bst               ] START   Caching artifact
[00:00:00][2f643c2d][   build:base/alpine.bst               ] SUCCESS Caching artifact
[00:00:00][2f643c2d][   build:base/alpine.bst               ] SUCCESS composition/base-alpine/2f643c2d-build.20240522-094354.log
[--:--:--][82d7d342][   build:base.bst                      ] START   composition/base/82d7d342-build.20240522-094354.log
[--:--:--][82d7d342][   build:base.bst                      ] START   Caching artifact
[00:00:00][82d7d342][   build:base.bst                      ] SUCCESS Caching artifact
[00:00:00][82d7d342][   build:base.bst                      ] SUCCESS composition/base/82d7d342-build.20240522-094354.log
[--:--:--][0babd9cc][   build:libhello.bst                  ] START   composition/libhello/0babd9cc-build.20240522-094354.log
[--:--:--][0babd9cc][   build:libhello.bst                  ] START   Staging dependencies at: /
[00:00:00][0babd9cc][   build:libhello.bst                  ] SUCCESS Staging dependencies at: /
[--:--:--][0babd9cc][   build:libhello.bst                  ] START   Integrating sandbox
[00:00:00][0babd9cc][   build:libhello.bst                  ] SUCCESS Integrating sandbox
[--:--:--][0babd9cc][   build:libhello.bst                  ] START   Staging sources
[00:00:00][0babd9cc][   build:libhello.bst                  ] SUCCESS Staging sources
[--:--:--][0babd9cc][   build:libhello.bst                  ] START   Running commands

    make PREFIX="/usr"
    make -j1 PREFIX="/usr" DESTDIR="/buildstream-install" install

[00:00:00][0babd9cc][   build:libhello.bst                  ] SUCCESS Running commands
[--:--:--][0babd9cc][   build:libhello.bst                  ] START   Caching artifact
[00:00:00][0babd9cc][   build:libhello.bst                  ] SUCCESS Caching artifact
[00:00:00][0babd9cc][   build:libhello.bst                  ] SUCCESS composition/libhello/0babd9cc-build.20240522-094354.log
[--:--:--][6fb0f24a][   build:hello.bst                     ] START   composition/hello/6fb0f24a-build.20240522-094355.log
[--:--:--][6fb0f24a][   build:hello.bst                     ] START   Staging dependencies at: /
[00:00:00][6fb0f24a][   build:hello.bst                     ] SUCCESS Staging dependencies at: /
[--:--:--][6fb0f24a][   build:hello.bst                     ] START   Integrating sandbox
[00:00:00][6fb0f24a][   build:hello.bst                     ] SUCCESS Integrating sandbox
[--:--:--][6fb0f24a][   build:hello.bst                     ] START   Staging sources
[00:00:00][6fb0f24a][   build:hello.bst                     ] SUCCESS Staging sources
[--:--:--][6fb0f24a][   build:hello.bst                     ] START   Running commands

    make PREFIX="/usr"
    make -j1 PREFIX="/usr" DESTDIR="/buildstream-install" install

[00:00:00][6fb0f24a][   build:hello.bst                     ] SUCCESS Running commands
[--:--:--][6fb0f24a][   build:hello.bst                     ] START   Caching artifact
[00:00:00][6fb0f24a][   build:hello.bst                     ] SUCCESS Caching artifact
[00:00:00][6fb0f24a][   build:hello.bst                     ] SUCCESS composition/hello/6fb0f24a-build.20240522-094355.log
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   composition/runtime-only/c22b89ed-build.20240522-094356.log
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   Staging dependencies
[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS Staging dependencies
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   Computing split
[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS Computing split
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   Integrating sandbox
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   Running commands

    ldconfig "/usr/lib"

[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS Running commands
[--:--:--][c22b89ed][   build:runtime-only.bst              ] INFO    Integration added 0 and removed 0 files
[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS Integrating sandbox
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   Creating composition

    Including files from domains: runtime
    Excluding orphaned files

[--:--:--][c22b89ed][   build:runtime-only.bst              ] INFO    Composing 287 files
[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS Creating composition
[--:--:--][c22b89ed][   build:runtime-only.bst              ] START   Caching artifact
[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS Caching artifact
[00:00:00][c22b89ed][   build:runtime-only.bst              ] SUCCESS composition/runtime-only/c22b89ed-build.20240522-094356.log
[00:00:08][        ][    main:core activity                 ] SUCCESS Build

Pipeline Summary
    Total:       5
    Session:     5
    Fetch Queue: processed 4, skipped 1, failed 0 
    Build Queue: processed 5, skipped 0, failed 0

As you can see in the output, this composition has only a few hundred files, but the complete alpine.bst runtime has several thousand files.

1.3.2. List the content

At the risk of this being a long list, let’s list the contents of this artifact

user@host:~/composition$ bst artifact list-contents runtime-only.bst

[--:--:--][        ][    main:core activity                 ] START   Loading elements
[00:00:00][        ][    main:core activity                 ] SUCCESS Loading elements
[--:--:--][        ][    main:core activity                 ] START   Resolving elements
[00:00:00][        ][    main:core activity                 ] SUCCESS Resolving elements
[--:--:--][        ][    main:core activity                 ] START   Initializing remote caches
[00:00:00][        ][    main:core activity                 ] SUCCESS Initializing remote caches
[--:--:--][        ][    main:core activity                 ] START   Query cache
[00:00:00][        ][    main:core activity                 ] SUCCESS Query cache
  runtime-only.bst:
	lib
	lib/ld-musl-x86_64.so.1
	usr
	usr/bin
	usr/bin/2to3
	usr/bin/2to3-3.6
	usr/bin/[
	usr/bin/[[
	usr/bin/aclocal
	usr/bin/aclocal-1.15
	usr/bin/addr2line
	usr/bin/ar
	usr/bin/as
	usr/bin/autoconf
	usr/bin/autoheader
	usr/bin/autom4te
	usr/bin/automake
	usr/bin/automake-1.15
	usr/bin/autoreconf
	usr/bin/autoscan
	usr/bin/autoupdate
	usr/bin/awk
	usr/bin/basename
	usr/bin/beep
	usr/bin/blkdiscard
	usr/bin/bunzip2
	usr/bin/bzcat
	usr/bin/bzip2
	usr/bin/c++filt
	usr/bin/c_rehash
	usr/bin/cal
	usr/bin/cc
	usr/bin/ccmake
	usr/bin/chvt
	usr/bin/cksum
	usr/bin/clear
	usr/bin/cmake
	usr/bin/cmp
	usr/bin/comm
	usr/bin/cpack
	usr/bin/cpio
	usr/bin/crontab
	usr/bin/cryptpw
	usr/bin/ctest
	usr/bin/cut
	usr/bin/dc
	usr/bin/deallocvt
	usr/bin/diff
	usr/bin/dirname
	usr/bin/dos2unix
	usr/bin/du
	usr/bin/dumpleases
	usr/bin/dwp
	usr/bin/easy_install-3.6
	usr/bin/eject
	usr/bin/elfedit
	usr/bin/env
	usr/bin/expand
	usr/bin/expr
	usr/bin/factor
	usr/bin/fallocate
	usr/bin/find
	usr/bin/flock
	usr/bin/fold
	usr/bin/free
	usr/bin/fuser
	usr/bin/gdbm_dump
	usr/bin/gdbm_load
	usr/bin/gdbmtool
	usr/bin/getconf
	usr/bin/getent
	usr/bin/gprof
	usr/bin/groups
	usr/bin/hd
	usr/bin/head
	usr/bin/hello
	usr/bin/hexdump
	usr/bin/hostid
	usr/bin/iconv
	usr/bin/id
	usr/bin/ifnames
	usr/bin/install
	usr/bin/ipcrm
	usr/bin/ipcs
	usr/bin/killall
	usr/bin/ld
	usr/bin/ld.bfd
	usr/bin/ldd
	usr/bin/less
	usr/bin/logger
	usr/bin/lsof
	usr/bin/lsusb
	usr/bin/lzcat
	usr/bin/lzma
	usr/bin/lzopcat
	usr/bin/m4
	usr/bin/make
	usr/bin/md5sum
	usr/bin/mesg
	usr/bin/microcom
	usr/bin/mkfifo
	usr/bin/mkpasswd
	usr/bin/nc
	usr/bin/nl
	usr/bin/nm
	usr/bin/nmeter
	usr/bin/nohup
	usr/bin/nproc
	usr/bin/nsenter
	usr/bin/nslookup
	usr/bin/objcopy
	usr/bin/objdump
	usr/bin/od
	usr/bin/openvt
	usr/bin/passwd
	usr/bin/paste
	usr/bin/patch
	usr/bin/perl
	usr/bin/perl5.26.1
	usr/bin/perldoc
	usr/bin/pgrep
	usr/bin/pip3
	usr/bin/pip3.6
	usr/bin/pkill
	usr/bin/pmap
	usr/bin/pod2html
	usr/bin/pod2man
	usr/bin/pod2text
	usr/bin/pod2usage
	usr/bin/podchecker
	usr/bin/podselect
	usr/bin/printf
	usr/bin/pscan
	usr/bin/pstree
	usr/bin/pwdx
	usr/bin/pydoc3
	usr/bin/pydoc3.6
	usr/bin/python3
	usr/bin/python3.6
	usr/bin/python3.6m
	usr/bin/pyvenv
	usr/bin/pyvenv-3.6
	usr/bin/ranlib
	usr/bin/readelf
	usr/bin/readlink
	usr/bin/realpath
	usr/bin/renice
	usr/bin/reset
	usr/bin/resize
	usr/bin/scanelf
	usr/bin/seq
	usr/bin/setkeycodes
	usr/bin/setsid
	usr/bin/sha1sum
	usr/bin/sha256sum
	usr/bin/sha3sum
	usr/bin/sha512sum
	usr/bin/showkey
	usr/bin/shred
	usr/bin/shuf
	usr/bin/size
	usr/bin/smemcap
	usr/bin/sort
	usr/bin/split
	usr/bin/ssl_client
	usr/bin/strings
	usr/bin/strip
	usr/bin/sum
	usr/bin/tac
	usr/bin/tail
	usr/bin/tcc
	usr/bin/tee
	usr/bin/test
	usr/bin/time
	usr/bin/timeout
	usr/bin/top
	usr/bin/tr
	usr/bin/traceroute
	usr/bin/traceroute6
	usr/bin/truncate
	usr/bin/tty
	usr/bin/ttysize
	usr/bin/udhcpc6
	usr/bin/unexpand
	usr/bin/uniq
	usr/bin/unix2dos
	usr/bin/unlink
	usr/bin/unlzma
	usr/bin/unlzop
	usr/bin/unshare
	usr/bin/unxz
	usr/bin/unzip
	usr/bin/uptime
	usr/bin/uudecode
	usr/bin/uuencode
	usr/bin/vi
	usr/bin/vlock
	usr/bin/volname
	usr/bin/wc
	usr/bin/wget
	usr/bin/which
	usr/bin/whoami
	usr/bin/whois
	usr/bin/xargs
	usr/bin/xmlwf
	usr/bin/xxd
	usr/bin/xzcat
	usr/bin/yes
	usr/lib
	usr/lib/libarchive.so.13
	usr/lib/libarchive.so.13.3.2
	usr/lib/libbfd-2.28.so
	usr/lib/libbz2.so.1
	usr/lib/libbz2.so.1.0.6
	usr/lib/libc.so
	usr/lib/libcrypto.so.42
	usr/lib/libcrypto.so.42.0.0
	usr/lib/libcurl.so.4
	usr/lib/libcurl.so.4.5.0
	usr/lib/libexpat.so.1
	usr/lib/libexpat.so.1.6.7
	usr/lib/libffi.so.6
	usr/lib/libffi.so.6.0.4
	usr/lib/libformw.so.6
	usr/lib/libformw.so.6.0
	usr/lib/libgcc_s.so.1
	usr/lib/libgdbm.so.4
	usr/lib/libgdbm.so.4.0.0
	usr/lib/libgdbm_compat.so.4
	usr/lib/libgdbm_compat.so.4.0.0
	usr/lib/libhello.so
	usr/lib/liblz4.so.1
	usr/lib/liblz4.so.1.8.0
	usr/lib/liblzma.so.5
	usr/lib/liblzma.so.5.2.3
	usr/lib/libmenuw.so.6
	usr/lib/libmenuw.so.6.0
	usr/lib/libncursesw.so.6
	usr/lib/libncursesw.so.6.0
	usr/lib/libopcodes-2.28.so
	usr/lib/libpanelw.so.6
	usr/lib/libpanelw.so.6.0
	usr/lib/libpython3.6m.so.1.0
	usr/lib/libpython3.so
	usr/lib/libreadline.so.7
	usr/lib/libreadline.so.7.0
	usr/lib/librhash.so.0
	usr/lib/libsqlite3.so.0
	usr/lib/libsqlite3.so.0.8.6
	usr/lib/libssh2.so.1
	usr/lib/libssh2.so.1.0.1
	usr/lib/libssl.so.44
	usr/lib/libssl.so.44.0.1
	usr/lib/libstdc++.so.6
	usr/lib/libstdc++.so.6.0.22
	usr/lib/libuv.so.1
	usr/lib/libuv.so.1.0.0
	usr/sbin
	usr/sbin/add-shell
	usr/sbin/addgroup
	usr/sbin/adduser
	usr/sbin/arping
	usr/sbin/brctl
	usr/sbin/chpasswd
	usr/sbin/chroot
	usr/sbin/crond
	usr/sbin/delgroup
	usr/sbin/deluser
	usr/sbin/ether-wake
	usr/sbin/fbset
	usr/sbin/fdformat
	usr/sbin/killall5
	usr/sbin/loadfont
	usr/sbin/lspci
	usr/sbin/nanddump
	usr/sbin/nandwrite
	usr/sbin/nbd-client
	usr/sbin/ntpd
	usr/sbin/partprobe
	usr/sbin/powertop
	usr/sbin/rdate
	usr/sbin/rdev
	usr/sbin/readahead
	usr/sbin/readprofile
	usr/sbin/remove-shell
	usr/sbin/rfkill
	usr/sbin/sendmail
	usr/sbin/setfont
	usr/sbin/setlogcons
	usr/sbin/update-ca-certificates

Some things to observe here:

  • The list does include the /usr/bin/hello program and also the /usr/lib/libhello.so shared library.

    These paths are both captured by the default split rules for the runtime domain.

  • The list does not include the /usr/include/libhello.h header file which was used to compile /usr/bin/hello.

    The header file is not captured by the runtime domain by default. It is however captured by the devel domain.

  • The runtime linker /lib/ld-musl-x86_64.so.1, as this was explicitly added to the runtime domain for the base/alpine.bst element which provides this file.

Tip

The reader at this time might want to list the content of other elements built from this project, such as the hello.bst element by itself, or the base/alpine.bst element.

1.3.3. Run the program

Finally, lets just run the program we built.

user@host:~/composition$ bst shell runtime-only.bst -- hello audience

[--:--:--][        ][    main:core activity                 ] START   Loading elements
[00:00:00][        ][    main:core activity                 ] SUCCESS Loading elements
[--:--:--][        ][    main:core activity                 ] START   Resolving elements
[00:00:00][        ][    main:core activity                 ] SUCCESS Resolving elements
[--:--:--][        ][    main:core activity                 ] START   Initializing remote caches
[00:00:00][        ][    main:core activity                 ] SUCCESS Initializing remote caches
[--:--:--][        ][    main:core activity                 ] START   Query cache
[00:00:00][        ][    main:core activity                 ] SUCCESS Query cache
[--:--:--][c22b89ed][    main:runtime-only.bst              ] START   Staging dependencies
[00:00:00][c22b89ed][    main:runtime-only.bst              ] SUCCESS Staging dependencies
[--:--:--][c22b89ed][    main:runtime-only.bst              ] START   Integrating sandbox
[00:00:00][c22b89ed][    main:runtime-only.bst              ] SUCCESS Integrating sandbox
[--:--:--][c22b89ed][    main:runtime-only.bst              ] STATUS  Running command

    hello audience

Hello audience

Here we can see that we at least have the required files to run our hello world program, however we would not have if we were missing the runtime linker which we added in base/alpine.bst.

1.4. Summary

In this chapter we’ve gotten familiar with split rules annotations, and we’ve learned enough about the compose element such that we can start creating our own compositions using split domains.

We’ve also used the list append directive and we are now observing the contents of artifacts using bst artifact list-contents.