Updating .NET Core inside AppVeyor

I currently use appveyor to run Continuous Integration builds for FluentValidation. It’s really easy to get started with appveyor as the build images come pre-installed with most tools you’d want to use as part of a build. The downside is it’s not easy to specify which version of a particular tool you want to use, and appveyor often lags behind with new releases.

For example, for FluentValidation I want the master branch to be built against the current LTS version of the .NET Core SDK (2.1.400), and I want my vNext branch to build against 2.2-preview1. But appveyor only has version 2.1.300 installed, so both branches need a new version of the .NET SDK.

Based on this post by Andrew Lock, I updated the FluentValidation build script to download an install a newer .NET Core SDK if needed. The build script uses powershell with the posh-build helpers for defining targets:

target install-dotnet-core {
  # Ensures that .net core is up to date.
  # first get the required version from global.json
  $json = ConvertFrom-Json (Get-Content "$path/global.json" -Raw)
  $required_version = $json.sdk.version

  # Running dotnet --version stupidly fails if the required SDK version is higher 
  # than the currently installed version. So move global.json out the way 
  # and then put it back again 
  Rename-Item "$path/global.json" "$path/global.json.bak"
  $current_version = (dotnet --version)
  Rename-Item "$path/global.json.bak" "$path/global.json"
  Write-Host "Required .NET version: $required_version Installed: $current_version"

  if ($current_version -lt $required_version) {
    # Current installed version is too low.
    # Install new version as a local only dependency. 
    $urlCurrent = "https://dotnetcli.blob.core.windows.net/dotnet/Sdk/$required_version/dotnet-sdk-$required_version-win-x64.zip"
    Write-Host "Installing .NET Core $required_version from $urlCurrent"
    $env:DOTNET_INSTALL_DIR = "$path/.dotnetsdk"
    New-Item -Type Directory $env:DOTNET_INSTALL_DIR -Force | Out-Null
    (New-Object System.Net.WebClient).DownloadFile($urlCurrent, "dotnet.zip")
    Write-Host "Unzipping to $env:DOTNET_INSTALL_DIR"
    Add-Type -AssemblyName System.IO.Compression.FileSystem; [System.IO.Compression.ZipFile]::ExtractToDirectory("dotnet.zip", $env:DOTNET_INSTALL_DIR)

Here I do the following:

  • Check which version of .net core is needed based on what’s defined in my global.json
  • Check the current .net core installed version (working around that dotnet --version fails if there’s a mismatch between required and expected version)
  • Download the new SDK and unzip it to a local directory
  • Update the environment PATH variable so that the new version is used whenever dotnet is called.

This script can then be called as part of the install section of your appveyor.yml.

The full example is available in the FluentValidation repository.

Written on August 28, 2018