AutoIncrementing Build with Core and DevOps Pipeline - msbuild

Question

I'm trying to setup an auto-incrementing version number for my ASP.NET Core 3.1 web app built using Azure Pipelines. I've tried various snippets and pipeline tasks and got as far as generating the version number but my build fails with the message
The specified version string does not conform to the required format - major[.minor[.build[.revision]
I'm using the below snippet of yml to generate the version number:
variables:
solution: '**/*.sln'
buildPlatform: 'Any CPU'
buildConfiguration: 'Release'
version.MajorMinor: '1' # Manually adjust the version number as needed for semantic versioning. Revision is auto-incremented.
version.Revision: $[counter(variables['version.MajorMinor'], 0)]
versionNumber: '$(version.MajorMinor).$(version.Revision)'
steps:
- task: PowerShell#2
displayName: Set the name of the build (i.e. the Build.BuildNumber)
inputs:
targetType: 'inline'
script: |
$doy = (Get-Date).DayofYear
Write-Host "##vso[task.setvariable variable=DayOfYear]$doy"
$rev = $env:BUILD_BUILDNUMBER.Split('.')[-1]
Write-Host "##vso[task.setvariable variable=Revision]$rev
Write-Host "set Revision to $rev"
[string] $buildName = "$(versionNumber).$doy.$rev"
Write-Host "Setting the name of the build to '$buildName'."
Write-Host "##vso[build.updatebuildnumber]$buildName"
This does generate a version number (1.26.199.50), however when I get the the MSBuild task:
task: VSBuild#1
inputs:
solution: '$(solution)'
msbuildArgs: '/p:DeployOnBuild=true /p:WebPublishMethod=Package /p:PackageAsSingleFile=true /p:SkipInvalidConfigurations=true /p:DesktopBuildPackageLocation="$(build.artifactStagingDirectory)\WebApp.zip" /p:DeployIisAppPath="Default Web Site" /p:Version=$(buildName)'
I get the version error. I've even tried replacing the version with 1.0.199.50 but I get the same error. I understand that each segment has to be less than 65534 as that's the max value for a UInt so I don't understand why it's failing.

Answer 1

After much frustration, I did this with a Powershell script in the release pipeline instead. I've got a Powershell task containing the below which is before the File Transform task. Steps to get it working.
Add a release pipeline variable called "MajorVersion". This is the first part of the version string
Add a property to appsettings.json called AppConfig.Version, set it to whetever for local testing.
Add a powershell task. The order should be Powershell Task->File Transform->App Service Deploy:
$doy = $(Get-Date).DayofYear
[string] $buildName = "$Env:MajorVersion.$doy.$Env:BUILD_BUILDNUMBER"
Write-Host "##vso[task.setvariable variable=AppConfig.Version;]$buildName"
Access the variable from your app settings using your preferred method. In core, probably via Configuration.GetSection("blah")
The assembly isn't stamped with the version, but you can get to it to display on the UI. I feel like this needs to be simplified by MS as auto-incrementing a version shouldn't be so difficult.