Allow MOI.ModelLike as the optimizer instead of MOI.AbstractOptimizer (…

…#3667)

src/JuMP.jl

@@ -84,7 +84,7 @@ value_type(::Type{<:AbstractModel}) = Float64
 mutable struct GenericModel{T<:Real} <: AbstractModel
     # In MANUAL and AUTOMATIC modes, CachingOptimizer.
     # In DIRECT mode, will hold an AbstractOptimizer.
-    moi_backend::MOI.AbstractOptimizer
+    moi_backend::MOI.ModelLike
     # List of shapes of constraints that are not `ScalarShape` or `VectorShape`.
     shapes::Dict{MOI.ConstraintIndex,AbstractShape}
     # List of bridges to add in addition to the ones added in

src/optimizer_interface.jl

@@ -444,6 +444,15 @@ function optimize!(
     if mode(model) != DIRECT && MOIU.state(backend(model)) == MOIU.NO_OPTIMIZER
         throw(NoOptimizer())
     end
+    optimizer = unsafe_backend(model)
+    if !(optimizer isa MOI.AbstractOptimizer)
+        error(
+            "Cannot call `optimize!` because the provided optimizer is not " *
+            "a subtype of `MOI.AbstractOptimizer`.\n\nThe optimizer is:\n\n" *
+            sprint(show, optimizer) *
+            "\n",
+        )
+    end
     try
         MOI.optimize!(backend(model))
     catch err

src/print.jl

@@ -273,7 +273,12 @@ function show_backend_summary(io::IO, model::GenericModel)
         println(io, "CachingOptimizer state: ", MOIU.state(backend(model)))
     end
     # The last print shouldn't have a new line
-    print(io, "Solver name: ", solver_name(model))
+    name = try
+        solver_name(model)
+    catch
+        "unknown"
+    end
+    print(io, "Solver name: ", name)
     return
 end
 

test/test_model.jl

@@ -1216,4 +1216,32 @@ function test_show_variable_not_owned()
     return
 end
 
+function test_direct_mps_model()
+    model = direct_model(MOI.FileFormats.MPS.Model())
+    @test occursin("unknown", sprint(show, model))
+    @variable(model, x >= 0)
+    io = IOBuffer()
+    write(io, backend(model))
+    seekstart(io)
+    data = String(take!(io))
+    @test startswith(data, "NAME")
+    @test endswith(data, "ENDATA\n")
+    return
+end
+
+function test_caching_mps_model()
+    model = Model(MOI.FileFormats.MPS.Model)
+    @test occursin("unknown", sprint(show, model))
+    @variable(model, x >= 0)
+    @test_throws(
+        ErrorException(
+            "Cannot call `optimize!` because the provided optimizer is not " *
+            "a subtype of `MOI.AbstractOptimizer`.\n\nThe optimizer is:\n\n" *
+            "A Mathematical Programming System (MPS) model\n",
+        ),
+        optimize!(model),
+    )
+    return
+end
+
 end  # module TestModels