Regression between MOI 0.9.20 and 0.9.21, still present with 0.9.22

[dourouc05]

It's probably one of the strangest errors I've ever seen in Julia. While working on ConstraintProgrammingExtensions' bridges (code at commit JuliaConstraints/ConstraintProgrammingExtensions.jl@18eb085), I got this error when updating to MOI 0.9.22 (from 0.9.20):

LoadError: syntax: unsupported `const` declaration on local variable around C:\Users\Thibaut\.julia\packages\MathOptInterface\1EYfq\src\Utilities\struct_of_constraints.jl:269

The relevant line of struct_of_constraints.jl does not really contain a const declaration, but it's in a macro:

function $MOIU.constraints(

This is reproducible in the GitHub Actions test environment: https://github.com/dourouc05/ConstraintProgrammingExtensions.jl/runs/2704982333

With 0.9.20, I have no such error, only failing tests:

   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.0 (2021-03-24)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

(@v1.6) pkg> add MathOptInterface@0.9.20
    Updating registry at `C:\Users\Thibaut\.julia\registries\General`
    Updating git-repo `https://github.com/JuliaRegistries/General.git`
   Resolving package versions...
   Installed MathOptInterface ─ v0.9.20
    Updating `C:\Users\Thibaut\.julia\environments\v1.6\Project.toml`
  [b8f27783] ↓ MathOptInterface v0.9.21 ⇒ v0.9.20
    Updating `C:\Users\Thibaut\.julia\environments\v1.6\Manifest.toml`
  [6e4b80f9] ↓ BenchmarkTools v0.7.0 ⇒ v0.5.0
  [b8f27783] ↓ MathOptInterface v0.9.21 ⇒ v0.9.20
  Progress [========================================>]  9/9
9 dependencies successfully precompiled in 37 seconds (76 already precompiled)

julia> include(raw"C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl")
model = MOIB.Constraint.SingleBridgeOptimizer{ConstraintProgrammingExtensions.Bridges.BinPacking2MILPBridge{Int64}, MOIU.MockOptimizer{MILPModel{Int64}}}
with 0 constraint bridges
with inner model MOIU.MockOptimizer{MILPModel{Int64}}
MOIB.is_bridged(model, MOI.VectorOfVariables, CP.BinPacking{Int}) = true
FixedCapacityBinPacking2BinPacking: Error During Test at C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\set_fixedcapacitybinpacking.jl:1
  Got exception outside of a @test
  MathOptInterface.UnsupportedConstraint{MathOptInterface.VectorOfVariables, ConstraintProgrammingExtensions.FixedCapacityBinPacking{Int64}}: `MathOptInterface.VectorOfVariables`-in-`ConstraintProgrammingExtensions.FixedCapacityBinPacking{Int64}` constraint is not supported by the model.
  Stacktrace:
    [1] add_constraint(model::MILPModel{Int64}, f::MathOptInterface.VectorOfVariables, s::ConstraintProgrammingExtensions.FixedCapacityBinPacking{Int64})
      @ MathOptInterface.Utilities ~\.julia\packages\MathOptInterface\5WwpK\src\Utilities\model.jl:674
    [2] add_constraint(mock::MathOptInterface.Utilities.MockOptimizer{MILPModel{Int64}}, func::MathOptInterface.VectorOfVariables, set::ConstraintProgrammingExtensions.FixedCapacityBinPacking{Int64})
      @ MathOptInterface.Utilities ~\.julia\packages\MathOptInterface\5WwpK\src\Utilities\mockoptimizer.jl:124
    [3] add_constraint(b::MathOptInterface.Bridges.Constraint.SingleBridgeOptimizer{ConstraintProgrammingExtensions.Bridges.BinPacking2MILPBridge{Int64}, MathOptInterface.Utilities.MockOptimizer{MILPModel{Int64}}}, f::MathOptInterface.VectorOfVariables, s::ConstraintProgrammingExtensions.FixedCapacityBinPacking{Int64})
      @ MathOptInterface.Bridges ~\.julia\packages\MathOptInterface\5WwpK\src\Bridges\bridge_optimizer.jl:1345
    [4] macro expansion
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\set_fixedcapacitybinpacking.jl:26 [inlined]
    [5] macro expansion
      @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
    [6] top-level scope
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\set_fixedcapacitybinpacking.jl:2
    [7] include(fname::String)
      @ Base.MainInclude .\client.jl:444
    [8] macro expansion
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\Bridges.jl:29 [inlined]
    [9] macro expansion
      @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
   [10] macro expansion
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\Bridges.jl:29 [inlined]
   [11] macro expansion
      @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
   [12] top-level scope
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\Bridges.jl:2
   [13] include(fname::String)
      @ Base.MainInclude .\client.jl:444
   [14] macro expansion
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:17 [inlined]
   [15] macro expansion
      @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
   [16] top-level scope
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:17
   [17] include(fname::String)
      @ Base.MainInclude .\client.jl:444
   [18] top-level scope
      @ REPL[2]:1
   [19] eval
      @ .\boot.jl:360 [inlined]
   [20] eval_user_input(ast::Any, backend::REPL.REPLBackend)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:139
   [21] repl_backend_loop(backend::REPL.REPLBackend)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:200
   [22] start_repl_backend(backend::REPL.REPLBackend, consumer::Any)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:185
   [23] run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:317
   [24] run_repl(repl::REPL.AbstractREPL, consumer::Any)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:305
   [25] (::Base.var"#874#876"{Bool, Bool, Bool})(REPL::Module)
      @ Base .\client.jl:387
   [26] #invokelatest#2
      @ .\essentials.jl:708 [inlined]
   [27] invokelatest
      @ .\essentials.jl:706 [inlined]
   [28] run_main_repl(interactive::Bool, quiet::Bool, banner::Bool, history_file::Bool, color_set::Bool)
      @ Base .\client.jl:372
   [29] exec_options(opts::Base.JLOptions)
      @ Base .\client.jl:302
   [30] _start()
      @ Base .\client.jl:485
Test Summary:                            | Pass  Error  Total
ConstraintProgrammingExtensions          |    3      1      4
  Bridges                                |    3      1      4
    BinPacking                           |    3      1      4
      FixedCapacityBinPacking2BinPacking |    3      1      4
ERROR: LoadError: Some tests did not pass: 3 passed, 0 failed, 1 errored, 0 broken.
in expression starting at C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:13

The full error message with MOI 0.9.21 or 0.9.22:

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.6.0 (2021-03-24)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> using ConstraintProgrammingExtensions
[ Info: Precompiling ConstraintProgrammingExtensions [b65d079e-ed98-51d9-b0db-edee61a5c5f8]

julia> include(raw"C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl")
ConstraintProgrammingExtensions: Error During Test at C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:13
  Got exception outside of a @test
  LoadError: syntax: unsupported `const` declaration on local variable around C:\Users\Thibaut\.julia\packages\MathOptInterface\1EYfq\src\Utilities\struct_of_constraints.jl:269
  Stacktrace:
    [1] top-level scope
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\Bridges.jl:1
    [2] include(fname::String)
      @ Base.MainInclude .\client.jl:444
    [3] macro expansion
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:17 [inlined]
    [4] macro expansion
      @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
    [5] top-level scope
      @ ~\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:17
    [6] include(fname::String)
      @ Base.MainInclude .\client.jl:444
    [7] top-level scope
      @ REPL[2]:1
    [8] eval
      @ .\boot.jl:360 [inlined]
    [9] eval_user_input(ast::Any, backend::REPL.REPLBackend)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:139
   [10] repl_backend_loop(backend::REPL.REPLBackend)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:200
   [11] start_repl_backend(backend::REPL.REPLBackend, consumer::Any)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:185
   [12] run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:317
   [13] run_repl(repl::REPL.AbstractREPL, consumer::Any)
      @ REPL C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\REPL\src\REPL.jl:305
   [14] (::Base.var"#874#876"{Bool, Bool, Bool})(REPL::Module)
      @ Base .\client.jl:387
   [15] #invokelatest#2
      @ .\essentials.jl:708 [inlined]
   [16] invokelatest
      @ .\essentials.jl:706 [inlined]
   [17] run_main_repl(interactive::Bool, quiet::Bool, banner::Bool, history_file::Bool, color_set::Bool)
      @ Base .\client.jl:372
   [18] exec_options(opts::Base.JLOptions)
      @ Base .\client.jl:302
   [19] _start()
      @ Base .\client.jl:485
  in expression starting at C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\Bridges\Bridges.jl:1
Test Summary:                   | Error  Total
ConstraintProgrammingExtensions |     1      1
ERROR: LoadError: Some tests did not pass: 0 passed, 0 failed, 1 errored, 0 broken.
in expression starting at C:\Users\Thibaut\.julia\dev\ConstraintProgrammingExtensions\test\runtests.jl:13

It started appearing with JuliaConstraints/ConstraintProgrammingExtensions.jl@18eb085, not before.

[blegat]

I think the offending line is:

MathOptInterface.jl/src/Utilities/model.jl

Line 1022 in cb82d81

:(const $esc_model_name{$T} = $generic)

It seems you cannot use MOIU.@model in a local scope, try removing it from the @testset scope.

[dourouc05]

Indeed, the strange error message disappears with more recent MOI 0.9. However, it does not explain why the error message started to appear with MOI 0.9.21…

[odow]

It seems you cannot use MOIU.@model in a local scope

Correct. You cannot declare variables as const in local scope, or create new types.

This is the problem:
JuliaConstraints/ConstraintProgrammingExtensions.jl@18eb085#diff-72e9fa7b42fded7918f9a3d34413266f1bcc95d23160eacd5b0653c5d5abc858R2-R27

I don't know why it worked previously, but it shouldn't have.

[dourouc05]

If it should never have worked, then the current situation is acceptable, thanks a lot for your quick help!