Release notes: Snapcraft 3.7

These are the release notes for Snapcraft 3.7, a significant update to Snapcraft 3.

For general details, including installation instructions, see Snapcraft overview, or take a look at Snapcraft release notes for other Snapcraft releases.

:information_source: Many of the improvements in this release are thanks to the great work done in collaboration with the attendees of the 2019 Snapcraft Summit that took place in Montreal.

New core features

Extended build options


Prior to the release of Snapcraft 3.7, using the base keyword within snapcraft.yaml to specify a base type for a snap did not take into account the creation of bases. Instead, the name keyword was arbitrarily used to determine the build environment:

name: core18
type: base
# base: is not set elsewhere 

The above example uses name to specify the creation of an Ubuntu 18.04 (core18) based build environment.

This fails if a base has yet to be bootstrapped, or is otherwise unavailable. For example, the following will currently generate a `launch failed: Unable to find an image matching “core20” error:

name: core20
type: base
# base: is not set elsewhere 

In cases like the above, where the base has not yet been bootstrapped, build-base can be used to explicitly define the base to use for the build environment.

To solve the above issue, for example, use the following:

name: core20
type: base
build-base: core18
# base: is not set elsewhere 


snapd is a new value for base type. Its inclusion will help the snapd team when using Snapcraft to build their own snap.

Extended metadata

The snapcraft.yaml schema has been extended to support new app properties added to snap.yaml, alongside better error handling and schema checks.

  • It’s now possible to specify the type string for the following existing options with an unspecified type:
    • stop-command
    • reload-command
  • Daemon options:
    • New daemon type: dbus
    • bus-name (for use with daemon: dbus). Uses regex pattern found in snapd
    • restart-delay
    • start-timeout
    • timer
    • watchdog-timeout
    • daemon dependencies can be specified as well as existing options (stop-timeout, restart-condition)
  • on-watchdog for restart-condition
  • autostart for apps installing autostart desktop files
  • regex patterns added to stop-timeout (to match introduced timeouts).

Faster LXD build iterations

When using Snapcraft with LXD and iterating over a build, a significant reduction in network overhead has resulted in much faster build times.

This is thanks to snapd 2.39 supporting API snap retrieval, and is used to avoid a root requirement when adding snaps to the build environment. It means snap don’t need to be re-downloaded as frequently.

Improved missing file experience

After the prime stage has completed, and missing dependencies are detected, Snapcraft now lists these as stage-packages, rather than as a simple list, for inclusion in snapcraft.yaml to hopefully build a functioning snap.

This will be extended in upcoming versions of Snapcraft to take into account plugs using the content interface.


crystal (new plugin)

Crystal is a programming language with a similar syntax to Ruby. This plugin was developed by Crystal’s upstream team to work with their recently released Crystal snap.

The following keyword is currently accepted by the plugin:

  • crystal-channel: (string) The Snap Store channel to install Crystal from. Default: latest/stable

Brian J. Cardiff, one of Crystal’s developers, attended the 2019 Snapcraft Summit Montréal and wrote an excellent overview of how to use the plugin as part of an event write-up. See Snapcraft Summit Montréal for the post.

conda (new plugin)

Conda is an open source package management system and environment management system that runs on Windows, macOS and Linux. This plugin was developed during the 2019 Snapcraft Summit Montréal with the Anaconda developers.

This plugin uses the following plugin-specific keywords:

  • conda-packages (list of strings) List of conda packages to install.
  • conda-python-version (string) The Python version to use for the conda packages. Defaults to the latest supported by Miniconda.
  • conda-miniconda-version (string) The version of Miniconda to bootstrap. Defaults to the latest release.


The Rust plugin has been reviewed by a Rust developer and their suggestions incorporated into this release.

One such improvement is defaulting to use the rust-toolchain file (if present), unless explicitly overridden by use of rust-channel or rust-revision.

Rebuilding is now also possible using this plugin.


The Ant publisher has released an Ant snap and reviewed the Ant plugin. Consequently, the Ant plugin has been updated to support the use of this new snap for building Ant-based projects.

The following new keywords are now accepted by the plugin:

  • ant-channel (string) If not using the Ant tarball from the Ant archive (see ant-version and ant-version-checksum, this keyword specifies the channel to use for ant in the Snap Store. Default: latest/stable


Support for ROS 2 Dashing Diademata was added to the colcon plugin in order to support this latest ROS release.

Bug fixes

There have been many bugs fixed in this release. Some of the most significant are as follows:

  • improved error handling
  • additional AppStream icon extraction scenarios that are now taken into account
  • modified handling of in-snap symlinks, specifically to better accommodate the merged /usr directory scheme
  • click.prompt and click.confirm expanded to query the existence of tty for stdin.

Full list of changes

The full list of features and issues worked on in this release are listed below.

List of changes for Snapcraft 3.7

Sergio Schvezov

  • static: use beta channel for black (#2606)
  • catkin spread tests: dump apt-config on failures for legacy (#2610)
  • rust plugin: use toml to dump the config (#2611)
  • rust plugin: use rust-toolchain by default if present (#2613)
  • conda plugin: new plugin (#2608)
  • build providers: support injection for LXD (#2621)
  • schema: remove support for os when using bases (#2626)
  • appstream extractor: skip non icon file paths (#2630)
  • spread tests: enable LXD build provider tests (#2631)
  • build environment: detect base type and use name as base
  • plugins: use get_build_base to determine base support
  • project: add support for build-base
  • repo: add support for querying file ownership
  • pluginhandler: suggest stage-packages for missing DT_NEEDED
  • tests: add python3-toml for autopkgtests
  • spread tests: limit conda plugin to non autopkgtests x86-64 systems
  • spread tests: crystal tests should only run on x86-64

Chris Patterson

  • black: minor format changes from updated black (#2603)
  • sources: introduce SnapcraftSourceNotFoundError (#2604)
  • spread: use more workers to reduce job times
  • catkin/legacy-pull: set test to manual
  • cli: convert users of click.confirm/prompt to echo.confirm/prompt
  • echo: respect SNAPCRAFT_HAS_TTY for is_tty_connected()
  • ant plugin: switch to using ant snap for building (by default)
  • general spread tests: set base for cwd test (#2618)
  • errors: refactor exception/error handling (#2602)
  • tests/unit/pluginhandler: introduce tests to repro symlink preservation bug
  • file_utils/create_similar_directory: drop follow_symlinks option
  • pluginhandler: honour symlink directory paths for filesets (LP: #1833408)
  • test_pluginhandler: remove faulty (redundant) tests
  • schema: synchronizing snapd supported schema to snapcraft (#2627)

Brian J. Cardiff

  • crystal plugin: new plugin (#2598)

Mike Miller

  • build providers: enforce well-known temp dir (#2607) (LP: #1833292)

Pawel Stolowski

  • schema: allow snapd as snap type (#2609)

Claudio Matsuoka

  • echo: add wrappers for click.prompt() and click.confirm()

Kyle Fazzari

  • colcon plugin: add support for dashing (#2593)

Anatoly Techtonik

  • cli: add -h short option for help (#2527) (LP: #1807423)

Stefan Bodewig

  • use the stable risk level now that ant has been released

Chris MacNaughton

  • rust plugin: add ability to rebuild (#2620) (LP: #1825858)

Carlo Lobrano

  • tools: let skip unnecessary steps (#2625)