Force recompilation when deps.jl changes

[ExpandingMan]

It's really nice that this is now downloading an artifact, however it's really screwing up a case in which I have an older computer server running which is incompatible with 0.9.5.

I was hoping that by setting GUROBI_HOME when Gurobi.jl gets built it would use that and not try to use the artifact, however I couldn't seem to get it to do this.

I suggest

• If no GUROBI_HOME is set, use artifacts as it currently does.
• If GUROBI_HOME is set, skip artifacts and just use that.

[ExpandingMan]

Looks like what I described above was intended... seems to be a very strange bug... _DEPS_FILE exists but it is using the artifact version of ligburobi... very weird...

[ExpandingMan]

Figured it out... apparently Julia bakes the value of libgurobi into the pre-compile cache. For this package, this should probably be circumvented so that one can change the binary location just by doing Pkg.build("Gurobi"), though I'm not sure what is the most appropriate way of doing that.

[odow]

We use existing binaries if a deps.jl file is present:

Gurobi.jl/src/Gurobi.jl

Lines 7 to 8 in 1008e8c

	if isfile(_DEPS_FILE)
	include(_DEPS_FILE)

so that one can change the binary location just by doing Pkg.build("Gurobi")

Does this not work? If re-building a package doesn't force recompilation, that should be a Julia problem. I don't think we can fix that in Gurobi.jl.

I don't have a linux machine to test this further, unfortunately.

[ExpandingMan]

Like I said, I actually had to delete the pre-compile cache before it would use a new value for libgurobi. This seems like it warrants a fix, but I'm not sure what the best way of fixing it is. A solution which would certainly work but is rather hackish and seems liable to have undesirable side effects would be to just delete the pre-compile cache (I'm not sure off the top of my head if there is a Pkg API call for this).

I will ask around on zulip and slack, I'm sure someone will know what the "right" way of doing this is.

[odow]

If re-building a package doesn't force recompilation, that should be a Julia problem

I'd regard this as a bug in Julia. Is this something we can actually fix in Gurobi.jl?

[ExpandingMan]

It's a bit more subtle than that, the *.ji files don't actually store compiled code. Furthermore I don't think const is intended to be used this way, it probably should be a Ref that gets selected when the package initializes.

Regardless, I see a few options here:

• Do nothing, but document the issue so that users can delete the *.ji cache manually as needed.
• Delete all gurobi *.ji files in the build script.
• Use a Ref and check the presence of the library at package initialization.

I took a look here for how other libraries deal with this, and, at least in the Vulkan example, it uses a Ref, though as that package is an automated wrapper it's a less than ideal comparison. Other examples I thought of all use jll and work a bit differently.

[odow]

Do you have a link to the slack conversation?

[ExpandingMan]

We had this conversation on zulip. Most of what I said here was from my own investigation. Someone more familiar with Pkg related stuff might still have something valuable to contribute here.

[odow]

We probably can make this work with an __init__ function. PRs accepted, but I have no plans to work on this.

The slack conversation (for the next few days before it gets purged) is: https://julialang.slack.com/archives/CBF3Z1D7V/p1637523109151900

[odow]

@KristofferC 's suggestion from slack is to use https://docs.julialang.org/en/v1/base/base/#Base.include_dependency.