Show a better error with invalid SupportedOSPlatformVersion values

[rolfbjarne]

A SupportedOSPlatformVersion value with a newline:

    <SupportedOSPlatformVersion>
13.0</SupportedOSPlatformVersion>

will make the build fail with:

    ILLink : unknown error IL7000: An error occurred while executing the custom linker steps. Please review the build log for more information.
    ILLINK : error MT2301: The linker step 'Setup' failed during processing: Invalid syntax for line 12 in /Users/rolf/test/dotnet/ios-plain/obj/Debug/net9.0-ios/iossimulator-arm64/custom-linker-options.txt: No equals sign.
    /Users/rolf/packages/microsoft.net.illink.tasks/9.0.6/build/Microsoft.NET.ILLink.targets(96,5): error NETSDK1144: Optimizing assemblies for size failed.

which is not helpful at all.

We should show a better error here.

binlog:

msbuild.binlog.zip

[Luckre]

Why is the minimum supported iOS version set to 13? If you review Apple’s device history:
https://en.wikipedia.org/wiki/List_of_iPhone_models
You’ll see that no currently supported iPhone or iPad is limited to iOS 13. For example, the iPhone 6 only supports up to iOS 12, while the iPhone 6s supports up to iOS 15. Given that iOS 13 is no longer relevant for most users, I recommend updating the minimum supported version to iOS 15. In practice, it's extremely rare to encounter devices still running iOS 13. Please consider forwarding this to your development team.

Thank you

[rolfbjarne]

Why is the minimum supported iOS version set to 13?

For this particular issue the problem isn't the number, but the newline next to it.