Calculate version inside an Azure DevOps pipeline using counter function

azure-pipelines.yaml

# Calculate version that will be incremented for each build whenever Major or Minor change, and different for each branch.
# Solution based on https://k2vacademy.com/2019/04/03/hidden-gems-in-azure-pipelines-creating-your-own-rev-variable-using-counter-expression-in-azure-pipelines/
# This could be useful if gitversion cannot be used.
# Otherwise the best solution is to use instead the default gitversion task: https://github.com/GitTools/actions/blob/main/docs/examples/azure/gitversion/execute/usage-examples.md

# ....

variables:
  # Versioning is handled using a format like major.minor.patch{-snapshot}
  # Major and Minor are fixed, patch is calculated using a counter (it will reset to 0 every time other values change).
  # Snapshot is populated with the branch when not main.
  VERSION_MAJOR: "0"
  VERSION_MINOR: "1"
  VERSION_PATCH: $[counter(format('{0}.{1}.{2}', variables['VERSION_MAJOR'], variables['VERSION_MINOR'], variables['Build.SourceBranchName']), 0)]
  ${{ if ne(variables['Build.SourceBranchName'], 'main') }}:
    VERSION_SNAPSHOT: $[format('-{0}', variables['Build.SourceBranchName'])]
  ${{ if eq(variables['Build.SourceBranchName'], 'main') }}:
    VERSION_SNAPSHOT: ""
  VERSION: $[format('{0}.{1}.{2}{3}', variables['VERSION_MAJOR'], variables['VERSION_MINOR'], variables['VERSION_PATCH'], variables['VERSION_SNAPSHOT'])]

# ....