Change:
jikes = callPackage ../development/compilers/jikes { }; <del> julia_06 = callPackage ../development/compilers/julia { gmp = gmp6; openblas = openblasCompat; inherit (darwin.apple_sdk.frameworks) CoreServices ApplicationServices; llvm = llvm_39; }; </del> julia_07 = callPackage ../development/compilers/julia/0.7.nix { gmp = gmp6; openblas = openblasCompat;

Discussion:
Right now we have three different versions of julia (0.6.4, 0.7.0, 1.0.1) in nixpkgs-unstable. However, the latest arpack update broke julia-0.6.4. Are all those versions of julia required or is it possible to remove old version? CC This is the build that broke julia-0.6
I don't know how to fix it, but I do need 0.6.4. I've just been pinning it for now.
Many Julia packages aren't updated for 1.0, or even 0.7 (as it's a slightly more compatible version of 1.0).
Is this still true? What packages, specifically? In my opinion 1.0.2 should be made the default version immediately on nixpkgs master I would be fine with earlier versions being dropped as well on nixpkgs master. Those that need them can install from older versions of nixpkgs julia 0.7 and 1.0 actually overspecify their dependencies, last I looked. Many pieces of the standard library were moved to packages, so FFTW, arpack, and a few others are not actually required on 0.7 and higher. EDIT: Also, it would be nice if aliases are set up such that --, so that multiple minor versions of julia can be installed in parallel in the future without the names breaking.
If 1.0 and 0.7 are so similar is it really necessary to keep julia 0.7? Looking ahead to release 18.09: what can we expect in terms of package support until February? Is it realistic to make 1.0 the main version until then?
Julia 0.7 is just a compatibility version of 1.0. They released simultaneously. I need 0.6 for a program I run, but AFAIK that program only needs , which is only broken on Windows and Mac. Though, does the Nix package support Mac? is pretty popular.
Most packages that are no longer in development only support 0.6. 0.7 took a while to release.
According to hydra builds on darwin.

Do I understand correctly that the current proposal is (for master): → → → (if the build can be fixed with reasonable effort; please ping me if a PR with a fix exists/ever appears) drop
Yes. Actually, I don't think it makes sense to have a since each 0.x version is incompatible with others. So just having is fine (for as long as julia 0.6 is kept in nixpkgs). Julia 0.7 is essentially equivalent to julia 1.0, except it contains warnings rather than errors for most syntax/methods that worked in julia 0.6. So the entire point of the release is to aid people in upgrading to julia 1.0. In this sense, it would be "nice" if were also available in the first release of nixpkgs that defaults to julia 1.0. But I have no personal stake in this.
OK, just changed the default to 1.0.1.
It'd be nice if a less hacky version of this gist was in Nixpkgs master.
Julia 0.6 is broken on master and release-19.03. This version is not supported by upstream anymore. Can it be removed? For everyone who still needs to run a legacy version can install it directly from the 18.09 channel. ()
Sure.