Force new submissions to have a `julia_compat`

[vchuravy]

We should force new recipes to have a julia_compat.
Many JLLs these days unnecessarily depend on Pkg, since their julia_compat is lower than 1.6

We should probably default to 1.6 / current LTS and require a manual julia_compat for lower.

cc: @KristofferC @giordano @staticfloat

[staticfloat]

I agree, we should default to 1.6 now.

[imciner2]

Many JLLs these days unnecessarily depend on Pkg, since their julia_compat is lower than 1.6

What is the build-date distribution of JLLs with these deps? Since we don't have a policy to rebuild JLLs periodically we can end up with older builds being the most recent version still.

I agree, we should default to 1.6 now.

Don't we already do this? I think I recall seeing new recipes coming in with the compat bound already in place.

[giordano]

Don't we already do this? I think I recall seeing new recipes coming in with the compat bound already in place.

The wizard always adds julia_compat="1.6" since JuliaPackaging/BinaryBuilder.jl#1047. But the default value of julia_compat is still "1.0", and I think it should remain like that for compatibility reasons: if we switched the default value, someone rebuilding an existing version of an old recipe which still doesn't explicitly set julia_compat it'll magically switch to a different julia_compat which would break existing packages without changing the version number as well.

Having a check for new recipes to specify julia_compat sounds good.

[vchuravy]

I think we should maybe change the default of julia_compat to be required so turn it into an error.

To encourage users to state their intention.

[giordano]

JuliaPackaging/BinaryBuilder.jl#1337