Recognize all supported versions of the .NET Framework 4.x

[CharliePoole]

Fixes #713

[rprouse]

Looks good. I'd love to know who uses this feature though 😄

[CharliePoole]

I wondered about that... for a long time we only distinguished net-4.0 and net-4.5, with the latter actually meaning "whatever version of 4.x you happen to have installed." I remember back when emulating 4.0 behavior under 4.5 was important to some people, causing us to make that distinction, but nobody has ever actually asked for this. OTOH, if we start checking TargetFrameworkAttribute, as @ChrisMaddoc has discussed, we'll find things like ".NETFramework,Version=v4.7.2" and end up saying we can't run the code without this fix.

[ChrisMaddock]

Thanks Charlie! Spotted a minor type, and got a couple of clarification questions - just keen to better understand what our current limitations are here. 🙂

[ChrisMaddock]

Am I reading this right, that this is to detect Mono 1.0? This is the sort of complexity I'd love to strip out, in a future iteration! 😅

[CharliePoole]

in principle, the CLR version doesn't necessarily have obvious relation to the framework version. You could have SomeFramework 1.0 with a CLR of 5.1234.5678. Mono was merely the first place where this showed up - Mono 1.0 is essentially equivalent to MS .NET 1.1.

Easiest way to simplify IMO is to figure out how to do without the CLR version entirely. In the meantime, I'm thinking of a change in my own engine where the individual Runtimes figure out the CLR version, so e.g. Mono.Runtime would have a method that allowed deducing the CLR version from the framework version. Otherwise, this code will get a lot more complicated for .NET Core and other runtimes we add.

[ChrisMaddock]

Great, thanks Charlie