GLPK.Optimizer should be verbose by default, according to MOI docs

Hi everyone, thank you for your work on this solver interface.

According to MathOptInterface documentation, all optimizers should be verbose by default:

Every optimizer should have verbosity on by default. For instance, if a solver has a solver-specific log level attribute, the MOI implementation should set it to 1 by default. If the user sets Silent to true, then the log level should be set to 0, even if the user specifically sets a value of log level.If the value of Silent is false then the log level set to the solver is the value given by the user for this solver-specific parameter or 1 if none is given.

https://jump.dev/MathOptInterface.jl/stable/reference/models/#MathOptInterface.Silent

GLPK.Optimizer, however, seems to be completely silent by default. For example, the following script produces no output:

using JuMP  # v0.21.8
using GLPK  # v0.14.8

model = Model(GLPK.Optimizer)
@variable(model, x, Bin)
@objective(model, Max, x)
optimize!(model)

Replacing GLPK in the snippet above by Cbc produces some output, as expected.

Should this be considered a bug, and would you consider a PR to fix it?

It's currently GLP_MSG_ERR by default.

GLPK.jl/src/MOI_wrapper/MOI_wrapper.jl

Line 183 in 5259d51

MOI.set(model, MOI.RawParameter("msg_lev"), GLP_MSG_ERR)

We could bump it up, I guess. Any reason? You can always use set_optimizer_attribute(model, "msg_lev", GLPK.GLP_MSG_ON) (or similar, I forget the exact constant).

Any reason?

It currently does not satisfy the MOI specs that says that it should be on by default.

I strongly dislike this change: https://github.com/odow/SDDP.jl/pull/407/checks?check_run_id=2703078270

GLP_MSG_ON is far too verbose. Which is probably why we had GLP_MSG_ERR in the first place.

For algorithms calling a same solvers many times like SDDP, it makes sense to use MOI.Silent

Yes, I've turned silent on by default now. The problem is still that GLPK is far too talky. It doesn't print a nice summary, it just spams the console with rows of numbers without context.

I'm not convinced that having the output on by default is an improvement:

julia> model = Model(GLPK.Optimizer)
A JuMP Model
Feasibility problem with:
Variables: 0
Model mode: AUTOMATIC
CachingOptimizer state: EMPTY_OPTIMIZER
Solver name: GLPK

julia> @variable(model, x >= 0)
x

julia> @variable(model, 0 <= y <= 3)
y

julia> @objective(model, Min, 12x + 20y)
12 x + 20 y

julia> @constraint(model, c1, 6x + 8y >= 100)
c1 : 6 x + 8 y ≥ 100.0

julia> @constraint(model, c2, 7x + 12y >= 120)
c2 : 7 x + 12 y ≥ 120.0

julia> print(model)
Min 12 x + 20 y
Subject to
 c1 : 6 x + 8 y ≥ 100.0
 c2 : 7 x + 12 y ≥ 120.0
 x ≥ 0.0
 y ≥ 0.0
 y ≤ 3.0

julia> optimize!(model)
      0: obj =   0.000000000e+00 inf =   2.200e+02 (2)
      3: obj =   2.120000000e+02 inf =   0.000e+00 (0)
*     4: obj =   2.050000000e+02 inf =   0.000e+00 (0)