daml/canton

Canton dependency

This folder (along with the canton entry in //deps.bzl) contains the infrastructure to work with custom Canton versions.

By default, we rely on the Canton artifact defined in //canton_dep.bzl. However, we have the ability to, rather than depend on a published version, depend on an arbitrary Canton build.

Local development

For local development, you can set the local attribute to True in canton_dep.bzl, and, rather than looking at the downloaded Canton release, the Bazel build will then look for a local file under canton/lib/canton.jar for its Canton source.

How you get that canton jar there is entirely up to you; the assumption is that this would be the result of building a local checkout of Canton with your own local, uncommitted changes.

Possibly something like:

mkdir -p $daml_checkout/canton/lib
cd $canton_checkout
nix-shell --max-jobs 2 --run "sbt community-app/assembly"
cp community/app/target/scala-*/canton-open-source-*.jar $daml_checkout/canton/lib/canton.jar

Once you have things working locally, you can push your Canton branch, and start building Daml against that even before the Canton branch gets merged.

CI

If you want your pull request to use a custom Canton commit, rather than a released snapshot, you can do that as follows. First, you need a Canton commit to point to in the Canton repo (it doesn't need to be on main, any commit on the GitHub repo can be used). Then:

• Make sure your branch sets the local key to True in canton_dep.bzl.
• Add a file called arbitrary_canton_sha to the root of the daml repository, that contains just the sha of the canton commit you want to build.

If the arbitrary_canton_sha file exists, the daml CI will clone the Canton repo, check out the corresponding sha, build the jar, and make it available to all three platforms. If the local attribute is set to True, just like locally, the CI builds will use the local canton.jar file instead of downloading the snapshot.

Main branch

Generally speaking, the main branch of the repo should depend on a published snapshot rather than a specific commit. However, there may be situations where we need to temporarily depend on a specific commit. To cater to those situations, the daily canton bump job will reset the daml repo to depend on the snapshot (i.e. if the tip of the main branch has an arbitrary_canton_sha file, the daily job will delete it as part of the canton bump PR, and likely it will set the local attibute back to False).

Enterprise Edition

Some situations may require running Canton Enterprise Edition, but this is an open-source repository so we cannot assume every contributor will have a Canton EE license key.

Tests that require Canton EE must be tagged with "canton-ee", which is disabled by default through .bazelrc. To run those tests locally, either explicitly target them or add --build_tag_filters= or --test_tag_filters= as appropriate (yes, these are the full options: by setting the "running" filters to empty for the current run, you overwrite the -canton-ee set in .bazelrc which excludes the Canton EE tests, thereby removing the exclusion and including the tests).

Those tests are run on CI.

If you're using a local build of canton (setting local to True per above) and you are explicitly overwriting the *_tag_filters to run the Canton EE tests, they will be run using your provided canton.jar (which therefore needs to be an EE jar at that point).