In my last post, I introduced the cf-autotick-bot, which tracks the version of packages on the conda-forge channel and automatically updates recipes with the most recent version of the source code. As I mentioned in my previous post, the bot achieves this by storing the conda-forge dependency graph along with metadata for each feedstock. With all of this information and the ability to PR to any feedstock, the bot has the potential for much more than just bumping the version.

The Migrator Class

Recently @CJ-Wright added the Migrator class to bot’s source code. Now, instead of explicity running the version bumping code on all feedstocks, the bot runs a set of Migrator instances on each feedstock. By putting the version bumping code in a subclass of Migrator, the bot can perform its original version bumping procedure, as well as migrations from any other inheritor of Migrator. This new paradigm allowed for the development of new functionality for the bot.

Conda-build 3 Compiler Syntax

Conda-build 3 defines a Jinja2 function to specify compiler packages. Recipes can include for example

    - {{ compiler('c') }}

which means the package needs to be built with C compilers.

Anaconda 5.0 switched from OS-provided compiler tools to their own compilers. Conda-forge does not yet use these compilers, but the core development team would like to switch to them. To do this, all recipes must first be using the new compiler syntax. Since the bot tracks every feedstock and issues PRs, it is a good tool to move recipes to this new syntax.

To give the bot this functionality, I wrote a Migrator subclass to handle this. The migrator first checks if a recipe needs to move to the new syntax by checking if it uses old compilers (toolchain or gcc), and then runs a conda-smithy command that updates the recipe with the new syntax. This is then PRed to the feedstock for the recipe maintainers to review.

I also wrote a migrator which simply bumps the build number of all recipes. This is useful when the switch is made to the new compilers, since all packages with compilers as build requirements would need to be rebuilt. The bot also makes sure that packages are rebuilt in dependency order, that is packages are only rebuilt after all of its requirements are rebuilt.

This rebuild migrator is useful in other situations besides this compiler switch. Whenever a pinning in conda-forge’s global pinning file is changed, packages must be rebuilt to use the new pinning. This migrator allows the bot to trigger rebuilds in the correct order of the descendants of the package in the global pinning.


Conda-forge allows pure-Python packages to be built noarch (no architecture), which mean the package only needs to built once (on CircleCI), making the build faster and freeing resources for other packages. A package can be built noarch simply by including noarch: python in the build section of the meta.yaml; however, there are many recipes on conda-forge which can be build with noarch, but do not include this in the build section. It would be ideal if any package is build noarch if possible, to reduce CI usage, especially in the age of the bot, which issues PRs in bulk, possible consuming a lot of CI resources.

Using the Migrator class, the can easily issue PRs adding noarch: python to the build section, so I wrote a migrator to do this. There are many requirements for a package to be noarch, summarized in this list

  • No compiled extensions
  • No post-link or pre-link or pre-unlink scripts
  • No OS specific build scripts
  • No python version specific requirements
  • No skips except for python version. (If the recipe is py3 only, remove skip statement and add version constraint on python)
  • 2to3 is not used
  • Scripts argument in is not used
  • If entrypoints are in, they are listed in meta.yaml
  • No activate scripts
  • Not a dependency of conda

The bot checks some of this criteria and skips PRing to feedstocks it knows cannot be noarch, but some of these requirements the bot cannot check with the metadata it currently collects. Therefore, the noarch PR is just a suggestion, and the PR message displays a checklist with the items above and asks the recipe maintainers to only merge if all items are satisfied. Otherwise, the recipe maintainers can close the PR and the bot will not issue another PR suggesting noarch.