Add LP Base.read! and tests

[guilhermebodin]

This implementation is some copy from https://github.com/odow/LPWriter.jl/blob/master/src/reader.jl

There are still a few missing important features.

• Obj constant
• SOS variables

I will probably implement them next week.

I have some questions regarding the files we use as test sets. Do you have any suggestions?

Closes #1675

[odow]

Just use my tests here? It includes some annoying files like https://github.com/odow/LPWriter.jl/blob/master/test/model1_tricky.lp

[odow]

Nice!

Most of these tests should be applicable:
https://github.com/odow/LPWriter.jl/blob/master/test/reader.jl

[odow]

@guilhermebodin what's the status of this? Do you want me to merge this as-is? Or are you going to benchmark the performance first?

[guilhermebodin]

Hi @odow, since we already have a working version, I think it is worth benchmarking this solution and compare with a new one without the TempLPModel. After revisiting the code, I believe there are no significant design changes, so it should not be an extensive rewrite of the current PR.

[odow]

Okay. So I'll hold off merging this then? Or do you want to work on that in a different PR?

[guilhermebodin]

I was not clear in the previous message, let's hold this PR for a couple days.

[guilhermebodin]

I have changed a few definitions using the file generated with this code

model = Model()
@variable(model, x[1:1_000] >= 0)
@constraint(model, con[i=1:200], sum(x) >= i)
@objective(model, Min, sum(x))

io = open("test_big.lp", "w")
write(
    io,
    model;
    format= MOI.FileFormats.FORMAT_LP
)

The modifications that made the biggest effect were in the function _tokenize and _get_variable_from_name .

[odow]

Looking better.

There's lots of untested error scenarios. We should add a bunch of malformed LP files to test the error conditions.

[odow]

This is an improvement on what we currently have so it's good by me. There are still a few opportunities to improve things (e.g., CacheLPModel has abstract fields, I don't know about the cost of try-catch, we could use more tests to improve coverage), but we can do them in separate, smaller PRs.

[guilhermebodin]

Just realized there exists a function Base.tryparse https://docs.julialang.org/en/v1/base/numbers/#Base.tryparse. I can rewrite the PR using this function.
Let's hold this PR until Monday and I will try to fix these issues today.

[odow]

Let's do improvements in a separate PR. This one is already quite big, and the functionality is stand-alone so there's no problem with merging it.