Trigger Job on file changes in Azure Devops

buildyamlsnippet.yaml

- job: ciml
    displayName: "Machine Learning CI"
    pool:
      vmImage: 'Ubuntu 20.04'
    steps: 
      - task: PowerShell@2
        displayName: 'Run CI Task from make.ps1 in Devcontainer'
        inputs:
          targetType: 'inline'
          script: 'Install-Module -Name PSake -Force && Invoke-psake ./make.ps1 ciml'
          errorActionPreference: 'stop'
          pwsh: true
          workingDirectory:  $(Build.SourcesDirectory) 
      - task: PowerShell@2
        displayName: 'Check if IMAGETAG.txt has changed since last build on main'
        env:
          System_AccessToken: $(System.AccessToken)
        inputs:
          targetType: 'filePath'
          filePath: ./scripts/build_scripts/changesSinceLastBuild.ps1
          arguments: >-
            -outputVariableName 'ML_IMAGE_TAG_CHANGED'
            -fileMatchExpression 'containers/IMAGETAG.txt'
            -branch 'refs/heads/main'
            -buildDefinitionId '20'
          errorActionPreference: 'stop'
          pwsh: true
          workingDirectory:  $(Build.SourcesDirectory)
      - task: AzurePowerShell@5
        condition: and(succeeded(), eq(variables['Build.SourceBranch'], 'refs/heads/main'), eq(variables.ML_IMAGE_TAG_CHANGED, 'true'))
        displayName: 'Build ML Container and Push to ACR'
        inputs:
          azureSubscription: $(azure_connection)
          ScriptType: 'inlineScript'
          pwsh: true
          inline: 'Install-Module -Name PSake -Force && Invoke-psake ./make.ps1 ciml-docker; exit (!$psake.build_success)'
          errorActionPreference: 'stop'
          workingDirectory: $(Build.SourcesDirectory)
          azurePowerShellVersion: 'LatestVersion'

changesSinceLastBuild.ps1

# This is an updated and tweaked version of a script designed to find if changes 
# have occurred since the last build. We've moved to the latest API and tweaked to spot changes in a file.
# Original Source: http://workingwithdevs.com/azure-devops-services-api-powershell-hosted-build-agents/

param(
    # The variable in AZDO to set when changes are found
    [string]$outputVariableName = "changesFound",
    # This can be 'containers/IMAGETAG.txt' or '.*/IMAGETAG.txt'. Expression is passed to powershell '-match' so valid regex NOT minimatch/glob
    [string]$fileMatchExpression = $env:FILE_TO_CHECK,
    # The build definition ID. In this case it's 20, look at the URL when editing a build to find it.
    [string]$buildDefinitionId = "20",
    [string]$branch = "refs/heads/main"
)

# Configuring this PS script to use the Azure DevOps Service Rest API
# Attempting to follow steps at: http://donovanbrown.com/post/how-to-call-team-services-rest-api-from-powershell

$pat = "Bearer $env:System_AccessToken"

# Set $env:LocalTest to test things out locally
if ($env:LocalTest) {
    # When testing locally use the below to authenticate
    $pat = $env:PAT_TOKEN # <- set this env to your pat token
    $pat = "Basic " + [System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes(":$pat"))
    $env:SYSTEM_TEAMFOUNDATIONCOLLECTIONURI = "https://dev.azure.com/{ORGNAME}/"
    $env:SYSTEM_TEAMPROJECTID = "{PROJECT NAME}"
    $env:BUILD_BUILDID = 1163 # <- pick the build you'd like to pretend to be
}

Write-Host $env:System_AccessToken

# Setting the script to authenticate using the system access token on the Azure DevOps Build Agent
# Note: Remember to set the agent job to "Allow scripts to access OAuth token" (under "Additional options")

# FINDING THE PREVIOUS SUCCESSFUL BUILD
#   Note: Combining double quotes and single quotes below because double quotes allow variable substitution 
#   (desired in first part) but single quotes do not (not desired in second part)
$env:SYSTEM_TEAMPROJECTID = [uri]::EscapeUriString($env:SYSTEM_TEAMPROJECTID)
$lastGreenBuildUrl = "$($env:SYSTEM_TEAMFOUNDATIONCOLLECTIONURI)$env:SYSTEM_TEAMPROJECTID/_apis/build/builds?branchName=$branch&definitions=$buildDefinitionId&queryOrder=finishTimeDescending&resultFilter=succeeded&api-version=6.0"

Write-Host "url: $lastGreenBuildUrl"
$data = Invoke-RestMethod -Uri "$lastGreenBuildUrl" -Headers @{Authorization = $pat}
Write-Host "Raw data returned from Green Build API call: $data"
$lastGreenBuild = $data.value.id | Select-Object -First 1
Write-Host "Last successfult build was $lastGreenBuild"

# FINDING ALL COMMITS SINCE THE LAST SUCCESSFUL COMMIT
$from = $lastGreenBuild
$to = $env:BUILD_BUILDID

Write-Host "from: $from"
Write-Host "to: $to"
$url = "$($env:SYSTEM_TEAMFOUNDATIONCOLLECTIONURI)$env:SYSTEM_TEAMPROJECTID/_apis/build/changes?fromBuildId=$from&toBuildId=$to&api-version=5.0-preview.2"
Write-Host "url: $url"

$commits = Invoke-RestMethod -Uri $url -Headers @{Authorization = $pat }

Write-Host "Raw data returned from API call: $commits"

# saving all commit ids into a list
$commitHashes = @()

foreach ($id in $commits.value) {
    $rawData = Get-Member -inputObject $id -name "id" | Out-String
    
    # $rawData is in format "string id=<hash>   ". We need to clean it up.
    $label, $hash = $rawData.Split("=")
    $hash = $hash.trim()
    
    # Adding $hash to $commitHashes
    $commitHashes += $hash
}

Write-Host "Commit hashes associated with this build:"
foreach ($hash in $commitHashes) {
    Write-Host $hash
}

# We can use this function to check if a given directory has been updated since last build
$lastCommit = $commitHashes | Select-Object -Last 1
$currentCommit = git rev-parse HEAD
$currentCommit = $currentCommit.Trim()

Write-Host "Finding files changed between $lastCommit and $currentCommit"

# Show diff between 
# See: https://stackoverflow.com/questions/3368590/show-diff-between-commits
$changedFiles = git diff $lastCommit^..$currentCommit --name-only

Write-Host "Changed files"
$changedFiles


# Check if the file we're interested in changed
$relevantChanges = $changedFiles -match $fileMatchExpression
if ($relevantChanges) {
    Write-Host ">>>>> CHANGED FOUND in file $fileMatchExpression since last successful build $from. Build var $outputVariableName set to 'true'"
    # Updating the build variables accordingly
    Write-Output ("##vso[task.setvariable variable=$outputVariableName;]true")
} else {
    Write-Host "No relevant changes found.. variable set to $changesFound"
}