Fetching contributors…
Cannot retrieve contributors at this time
369 lines (277 sloc) 13.8 KB
# -*- Mode:Python; indent-tabs-mode:nil; tab-width:4 -*-
# Copyright (C) 2015-2017 Canonical Ltd
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 3 as
# published by the Free Software Foundation.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <>.
"""Snapcraft plugins drive different build systems
Each part has a build system . Most parts are built from source using one of
a range of build systems such as CMake or Scons. Some parts are pre-built
and just copied into place, for example parts that reuse existing binary
You tell snapcraft which build system it must drive by specifying the
snapcraft plugin for that part. Every part must specify a plugin explicitly
(when you see a part that does not specify a plugin, that's because the
actual part definition is in the cloud, where the plugin is specified!)
These plugins implement a lifecycle over the following steps:
- pull: retrieve the source for the part from the specified location
- build: drive the build system determined by the choice of plugin
- stage: consolidate desirable files from all the parts in one tree
- prime: distill down to only the files which will go into the snap
- snap: compress the prime tree into the installable snap file
These steps correspond to snapcraft commands. So when you initiate a
'snapcraft pull' you will invoke the respective plugin for each part in
the snap, in sequence, to handle the source pull. Each part will then have a
fully populated parts/<part-name>/src/ directory. Similarly, if you then say
'snapcraft build' you will invoke the plugin responsible for each part in
turn, to build the part.
# Snapcraft Lifecycle
## Pull
In this first step, source material is retrieved from the specified
location, whether that is a URL for a tarball, a local path to a source tree
inside the snap, a revision control reference to checkout, or something
specific to the plugin such as PyPI. The plugin might also download
necessary artifacts, such as the Java SDK, which are not specific to the
particular part but which are needed by the plugin to handle its type of
build system.
All the downloaded content for each part goes into the
`parts/<part-name>/src/` directory, which acts as a cache to prevent
re-fetching content. You can clean that cache out with 'snapcraft clean'.
## Build
Snapcraft calculates an appropriate sequence to build the parts, based on
explicit 'after' references and the order of the parts in the
snapcraft.yaml. Each part is built in the `parts/<part-name>/build`
directory and installed into `parts/<part-name>/install`.
Note the install step - we might actually want to use built artifacts from
one part in the build process of another, so the `parts/<part-name>/install`
directory is useful as a 'working fresh install' of the part.
Between the plugin, the part definition YAML, and the build system of the
part, it is expected that the part can be built and installed in the right
At this point you have a tree under `parts/` with a subdirectory for every
part, and underneath those, separate src, build and install trees for each
## Stage
We now need to start consolidating the important pieces of each part into a
single tree. We do this twice - once in a very sweeping way that will
produce a lot of extraneous materials but is useful for debugging. This is
the 'stage' step of the lifecycle, because we move a lot of the build output
from each part into a consolidated tree under `stage/` which has the
structure of a snap but has way too much extra information.
The important thing about the staging area is that it lets you get all the
shared libraries in one place and lets you find overlapping content in the
parts. You can also try this directory as if it were a snap, and you'll have
all the debugging information in the tree, which is useful for developers.
Each part describes its own staging content - the files that should be
staged. The part will often describe "chunks" of content, called filesets,
so that they can be referred to as a useful set rather than having to call
out individual files.
## Prime
It is useful to have a directory tree which exactly mirrors the structure of
the final snap. This is the `prime/` directory, and the lifecycle includes a
'prime' step which copies only that final, required content from the
`stage/` directory into the `prime/` directory.
So the `prime/` directory contains only the content that will be put into
the final snap, unlike the staging area which may include debug and
development files not destined for your snap.
The snap metadata will also be placed in `./prime/meta` during the prime
step, so this `./prime` directory is useful for inspecting exactly what is
going into your snap or to conduct any final post-processing on snapcraft's
## Snap
The final step in the snapcraft lifecycle builds a snap out of the `prime/`
directory. It will be in the top level directory, alongside snapcraft.yaml,
called <name>-<version>-<arch>.snap
# Standard part definition keywords
There are several builtin keywords which can be used in any part regardless
of the choice of plugin.
- after: [part, part, part...]
Snapcraft will make sure that it builds all of the listed parts before
it tries to build this part. Essentially these listed dependencies for
this part, useful when the part needs a library or tool built by another
If such a dependency part is not defined in this snapcraft.yaml, it must
be defined in the cloud parts library, and snapcraft will retrieve the
definition of the part from the cloud. In this way, a shared library of
parts is available to every snap author - just say 'after' and list the
parts you want that others have already defined.
- build-packages: [pkg, pkg, pkg...]
A list of packages to install on the build host before building
the part. The files from these packages typically will not go into the
final snap unless they contain libraries that are direct dependencies of
binaries within the snap (in which case they'll be discovered via `ldd`),
or they are explicitly described in stage-packages.
- stage-packages: YAML list
A set of packages to be downloaded and unpacked to join the part
before it's built. Note that these packages are not installed on the host.
Like the rest of the part, all files from these packages will make it into
the final snap unless filtered out via the `snap` keyword.
One may simply specify packages in a flat list, in which case the packages
will be fetched and unpacked regardless of build environment. In addition,
a specific grammar made up of sub-lists is supported here that allows one
to filter stage packages depending on various selectors (e.g. the target
arch), as well as specify optional packages. The grammar is made up of two
nestable statements: 'on' and 'try'.
Let's discuss `on`.
- on <selector>[,<selector>...]:
- ...
- else[ fail]:
- ...
The body of the 'on' clause is taken into account if every (AND, not OR)
selector is true for the target build environment. Currently the only
selectors supported are target architectures (e.g. amd64).
If the 'on' clause doesn't match and it's immediately followed by an 'else'
clause, the 'else' clause must be satisfied. An 'on' clause without an
'else' clause is considered satisfied even if no selector matched. The
'else fail' form allows erroring out if an 'on' clause was not matched.
For example, say you only wanted to stage `foo` if building for amd64 (and
not stage `foo` if otherwise):
- on amd64: [foo]
Building on that, say you wanted to stage `bar` if building on an arch
other than amd64:
- on amd64: [foo]
- else: [bar]
You can nest these for more complex behaviors:
- on amd64: [foo]
- else:
- on i386: [bar]
- on armhf: [baz]
If your project requires a package that is only available on amd64, you can
fail if you're not building for amd64:
- on amd64: [foo]
- else fail
Now let's discuss `try`:
- try:
- ...
- else:
- ...
The body of the 'try' clause is taken into account only when all packages
contained within it are valid. If not, if it's immediately followed by
'else' clauses they are tried in order, and one of them must be satisfied.
A 'try' clause with no 'else' clause is considered satisfied even if it
contains invalid packages.
For example, say you wanted to stage `foo`, but it wasn't available for all
architectures. Assuming your project builds without it, you can make it an
optional stage package:
- try: [foo]
You can also add alternatives:
- try: [foo]
- else: [bar]
Again, you can nest these for more complex behaviors:
- on amd64: [foo]
- else:
- try: [bar]
- organize: YAML
Snapcraft will rename files according to this YAML sub-section. The
content of the 'organize' section consists of old path keys, and their
new values after the renaming.
This can be used to avoid conflicts between parts that use the same
name, or to map content from different parts into a common conventional
file structure. For example:
usr/oldfilename: usr/newfilename
usr/local/share/: usr/share/
The key is the internal part filename, the value is the exposed filename
that will be used during the staging process. You can rename whole
subtrees of the part, or just specific files.
Note that the path is relative (even though it is "usr/local") because
it refers to content underneath parts/<part-name>/install which is going
to be mapped into the stage and prime areas.
- filesets: YAML
When we map files into the stage and prime areas on the way to putting
them into the snap, it is convenient to be able to refer to groups of
files as well as individual files. Snapcraft lets you name a fileset
and then use it later for inclusion or exclusion of those files from the
resulting snap.
For example, consider man pages of header files.. You might want them
in, or you might want to leave them out, but you definitely don't want
to repeatedly have to list all of them either way.
This section is thus a YAML map of fileset names (the keys) to a list of
filenames. The list is built up by adding individual files or whole
subdirectory paths (and all the files under that path) and wildcard
globs, and then pruning from those paths.
The wildcard * globs all files in that path. Exclusions are denoted by
an initial `-`.
For example you could add usr/local/* then remove usr/local/man/*:
allbutman: [ usr/local/*, -usr/local/man/* ]
manpages: [ usr/local/man ]
Filenames are relative to the part install directory in
`parts/<part-name>/install`. If you have used 'organize' to rename files
then the filesets will be built up from the names after organization.
- stage: YAML file and fileset list
A list of files from a part install directory to copy into `stage/`.
Rules applying to the list here are the same as those of filesets.
Referencing of fileset keys is done with a $ prefixing the fileset key,
which will expand with the value of such key.
For example:
- usr/lib/* # Everything under parts/<part-name>/install/usr/lib
- -usr/lib/ # Excludng
- $manpages # Including the 'manpages' fileset
- snap: YAML file and fileset list
A list of files from a part install directory to copy into `prime/`.
This section takes exactly the same form as the 'stage' section but the
files identified here will go into the ultimate snap (because the
`prime/` directory reflects the file structure of the snap with no
extraneous content).
- build-attributes: [attribute1, attribute2]
A list of special attributes that affect the build of this specific part.
Supported attributes:
- no-install:
Do not run the install target provided by the plugin's build system.
Supported by: kbuild
- debug:
Plugins that support the concept of build types build in Release mode
by default. Setting the 'debug' attribute requests that they instead
build in Debug mode.
from collections import OrderedDict # noqa
import pkg_resources # noqa
def _get_version():
import os as _os
if _os.environ.get("SNAP_NAME") == "snapcraft":
return _os.environ["SNAP_VERSION"]
return pkg_resources.require("snapcraft")[0].version
except pkg_resources.DistributionNotFound:
return "devel"
# Set this early so that the circular imports aren't too painful
__version__ = _get_version()
from snapcraft._baseplugin import BasePlugin # noqa
# FIXME LP: #1662658
from snapcraft._store import ( # noqa
from snapcraft import common # noqa
from snapcraft import extractors # noqa
from snapcraft import plugins # noqa
from snapcraft import sources # noqa
from snapcraft import file_utils # noqa
from snapcraft import shell_utils # noqa
from snapcraft.internal import repo # noqa
from snapcraft.project._project_options import ProjectOptions # noqa