Cross Platform CI with CoreRT and AppVeyor

CoreRT is an ahead-of-time (AOT) compiler and runtime for .NET Core. It builds .NET Core applications into a single, small binary that runs without requiring .NET Core to be installed on the system. This makes distribution easy, especially to Mac OS and Linux, which may not have .NET Core installed. On all platforms, the program will have a faster start-up time and lower memory footprint.

Like most developers, I have a pet static site generator I’m working on. As it’s a command line utility that will be distributed to users that most likely won’t have .NET Core installed, I decided to try CoreRT. The initial setup was simple, but it took some time to figure out how to set up continuous integration (CI) on AppVeyor. I wanted the CI process to produce binaries artifacts from the master branch for each platform. As a bonus, if I tag a commit, it should build a release for each platform and post them to the GitHub Releases page.

One drawback of AppVeyor is that it does not yet support Mac OS. However, there are plans to support it sometime this year. I figure that if I have it working on both Windows and Linux, it should hopefully not be too difficult to add Mac OS support.

AppVeyor uses a YAML file for its configuration, and like most CI platforms, there’s more than one way to accomplish your goal. I found that the following configuration is a nice mixture of Don’t-Repeat-Yourself and maintainability:

version: '0.0.{build}'
clone_depth: 1
image:
  # Windows with VS2017
  - Visual Studio 2017
  # default version of 'ubuntu' is old for compatibility reasons. Specify the newest LTS.
  - ubuntu1804
branches:
  only:
  - master
# items prefixed with 'cmd:' run only on Windows
# items prefixed with 'sh:' run only on Ubuntu
init:
  - cmd: git config --global core.autocrlf true
install:
  # application dependencies
  - cmd: choco install pandoc
  - sh:  wget https://github.com/jgm/pandoc/releases/download/2.3.1/pandoc-2.3.1-1-amd64.deb && sudo dpkg -i pandoc-2.3.1-1-amd64.deb
  # corert dependencies https://github.com/dotnet/corert/blob/master/Documentation/prerequisites-for-building.md
  - sh:  sudo apt-get install -y clang libkrb5-dev
before_build:
  - dotnet --version
  - dotnet restore --verbosity m
build_script:
  - dotnet build
test_script:
  - cd Nessie.Tests
  - dotnet test
after_test:
  - cd ..
  - cmd: dotnet publish -c release -r win-x64 -o dist/windows
  # specifying the absolute path here is required to remove paths from archive
  - cmd: 7z a Nessie/dist/windows/nessie-windows-x64.zip %APPVEYOR_BUILD_FOLDER%/Nessie/dist/windows/nessie.exe
  # by default, CoreRT on linux tries to use clang-3.9, reset this to version independent
  # https://github.com/dotnet/corert/issues/5654
  - sh:  export CppCompilerAndLinker=clang
  - sh:  dotnet publish -c release -r linux-x64 -o dist/linux
  - sh:  7z a Nessie/dist/linux/nessie-linux-x64.zip $APPVEYOR_BUILD_FOLDER/Nessie/dist/linux/Nessie
# for / matrix docs
# https://www.appveyor.com/blog/2018/04/25/specialized-build-matrix-configuration-in-appveyor/
for:
  -
    matrix:
      only:
        - image: Visual Studio 2017
    artifacts:
     - path: 'Nessie/dist/windows/nessie-windows-x64.zip'
       name: nessie-windows

  -
    matrix:
      only:
        - image: ubuntu1804
    artifacts:
      - path: 'Nessie/dist/linux/nessie-linux-x64.zip'
        name: nessie-linux
deploy:
  provider: GitHub
  # encrypted token, it's ok to be in version control
  # https://ci.appveyor.com/tools/encrypt
  auth_token:
    secure: zQl909f8bNxmaKdpgiE730kw9vjsNvoV0SjwN/fk3lv9dy7d9cdhgo0/iz/apRqc
  artifact: nessie-windows, nessie-linux
  prerelease: true
  on:
    appveyor_repo_tag: true

I won’t go through this line-by-line, as hopefully the comments make everything clear. Here are the things that took me a while to figure out:

Use the image ubuntu1804 if you want up-to-date ubuntu. The normal ubuntu tag is still 16.04.
On Ubuntu, you need to run sudo apt-get install -y clang libkrb5-dev to get the required dependencies for CoreRT.
dotnet publish -c release -r RELEASE_ID will generate the binary files. See the RID Catalog for a list of valid operating system identifiers.
export CppCompilerAndLinker=clang is required if you don’t want to manually install an ancient version of clang on Ubuntu. This environment variable overrides the default Clang 3.9 that CoreRT uses by default.
For command line scripts, prefix sh: for Linux and cmd: for Windows. For platform-specific configurations that are not command line scripts (e.g. the artifacts configuration) you need to use AppVeyor’s matrix configuration. Essentially, the only is a filter, and the sibling tags like artifacts will take effect when the condition is true.
The deploy: configuration (for posting releases to github) requires the appveyor_repo_tag condition. Otherwise, a build on master branch would create a release and tag it in git. This tag would then trigger another build!
- Each commit to master will trigger a build. When you’re happy with master, tag the commit and push it. AppVeyor will then create a release on GitHub.

This is more of a brain dump than a blog post, but I hope this ends up being useful to other people out there working with CoreRT and AppVeyor!

tagged as csharp, corert, appveyor and continuous-integration