Support DOTNET_ prefix

[AaronRobinsonMSFT]

Fixes #47283

This enables support for using the DOTNET_ prefix and is now the preferred first choice. The COMPlus_ is still supported but is the fallback.

A new flag was created to ignore the DOTNET_ prefix in case external users have created a conflicting variable name.

• DOTNET_EnableDOTNETPrefix=0
• COMPlus_EnableDOTNETPrefix=0

[jkotas]

A new flag was created to ignore the DOTNET_ prefix in case external users have created a conflicting variable name.

I would not bother with this. If we find that there is a conflicting name, we should just fix it.

[jkotas]

Thank you!

[lambdageek]

Should we reserve the DOTNET_ prefix for variables that are accepted by both runtimes, and continue using COMPlus_ for CoreCLR (and the BCL) and MONO_ for MonoVM?

[AaronRobinsonMSFT]

@lambdageek That is an interesting split. @stephentoub, who filed the issue, thoughts?

[stephentoub]

Should we reserve the DOTNET_ prefix for variables that are accepted by both runtimes, and continue using COMPlus_ for CoreCLR (and the BCL) and MONO_ for MonoVM?

I would love for us to never utter "COMPlus" again 😄

If we feel we need to differentiate some values based on runtime, I could swallow having some be prefixed with CORECLR_ and some with MONO_, and then DOTNET_ for the general "applies everywhere" case. However, I worry such a split might lead to headaches over time, as settings initially only supported by one runtime shift to being supported everywhere (which we would generally hope to be the case as we further unify and smooth over differences). I also think it'd be potentially confusing for folks to learn about multiple prefixes and remember when to use which. And, there are other splits I don't necessarily want to change the prefix for, e.g. settings that only make sense on one OS and that are simply ignored on others.

[lambdageek]

Yea I think in the long term it will be bad to have multiple flag prefixes as we continue to converge. I don't, for the record, feel that it's a particularly bad idea to shift CoreCLR over to a DOTNET_ prefix.

I'm just apprehensive bug reports like "Setting DOTNET_GC_XYZ doesn't do anything on Android". But on the other hand that's really no different from "COMPlus_GC_XYZ doesn't do anything on Android" - either way we will need to do some work in Mono, or educate the customer, or both.

[AaronRobinsonMSFT]

either way we will need to do some work in Mono, or educate the customer, or both.

@lambdageek This is spot on. I am going to be writing up some official doc on these configs. The past week has been an amazing journey and this system is interesting to say the least. I am hoping the education can be as simple as "go to <URL> and read".

[AaronRobinsonMSFT]

crossgen2smoke failures are #50539