Add support for MOI.write_to_file (#265)

src/MOI_wrapper.jl

@@ -3179,6 +3179,12 @@ function MOI.set(model::Optimizer, attr::CallbackFunction, f::Function)
     return
 end
 
+function MOI.write_to_file(model::Optimizer, filename::String)
+    ret = Highs_writeModel(model, filename)
+    _check_ret(ret)
+    return
+end
+
 # These enums are deprecated. Use the `kHighsXXX` constants defined in
 # libhighs.jl instead.
 

test/MOI_wrapper.jl

@@ -1030,6 +1030,26 @@ function test_ObjectiveFunction_VectorAffineFunction_to_ScalarQuadraticFunction(
     return
 end
 
+function test_write_to_file()
+    dir = mktempdir()
+    model = HiGHS.Optimizer()
+    x, _ = MOI.add_constrained_variable(model, MOI.GreaterThan(1.0))
+    MOI.set(model, MOI.VariableName(), x, "x")
+    MOI.set(model, MOI.ObjectiveSense(), MOI.MIN_SENSE)
+    f = 1.0 * x + 2.0
+    MOI.set(model, MOI.ObjectiveFunction{typeof(f)}(), f)
+    filename = joinpath(dir, "model.mps")
+    MOI.write_to_file(model, filename)
+    contents = read(filename, String)
+    @test occursin("ENDATA", contents)
+    filename = joinpath(dir, "model.lp")
+    MOI.write_to_file(model, filename)
+    contents = read(filename, String)
+    @test occursin("obj:", contents)
+    @test occursin("bounds", contents)
+    return
+end
+
 end  # module
 
 TestMOIHighs.runtests()