[dotnet] Use the default .NET scheme for the default TargetPlatformVersion for library projects. #21343
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…brary projects. TODO: better description.
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…lt-target-platform-version-libraries
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…lt-target-platform-version-libraries
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rolfbjarne
changed the title
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@rolfbjarne I posted this on the MAUI channel twice and no objections received feel free to merge at your own convenience |
We must define the default platform version if it's not specified in the TFM, and according to the spec the default should not change for a given .NET version:
Basically: this should be the last OS version of the platform in question when the current major .NET version is first released to stable.
Ref: https://github.com/dotnet/designs/blob/8e6394406d44f75f30ea2259a425cb9e38d75b69/accepted/2020/net5/net5.md#os-versions
However, this doesn't work well for Apple platforms: Whenever Apple releases new Xcode versions, our existing workloads might not be compatible with the new Xcode. We'll of course ship updateds workload with support for the new Xcode, but defaulting to an older target platform version would mean that developers wouldn't get the new workload, they'd get the old one. This is exacerbated by the fact that Apple aggressively auto-updates Xcode on developers' machines: they might wake up one day to a broken build - the obvious fix ("dotnet workload update") doesn't fix anything - even if we've shipped updated workloads - because the default is to use the old one. They'd have to manually specify the target platform version in the target platform to get the updated workload ("net8.0-ios17.2" to use the iOS 17.2 workload instead of "net8.0-ios", which would use the default (old/initial/17.0) .NET 8 workload) - and then update again when the next Xcode comes around. At this point the point of having a sane default value is totally out the window, because everybody would have to specify (and continuously update) a platform version in their project files to keep their projects building.
So we've made the decision that the default target platform version is always the latest supported target platform version.
Given the previous example: once we've implemented and released support for iOS 18.1, the updated iOS workload will use 18.1 as the default TPV for iOS.
On the other hand, this turns out to be somewhat of a complication for library developers, because they typically don't need Xcode to build their projects, and if we auto-update their TargetPlatformVersion to the latest, then all their customers have to also update their workloads, which for some people end up being a rather nasty surprise (because with the above algorithm it happens without developer action). Thus we follow .NET's default platform version scheme for library projects: it won't change in minor .NET releases.
Related design/docs PRs: