[FileFormats.NL] fix reading file with no objective (#2391)

Author: odow

src/FileFormats/NL/read.jl

@@ -182,10 +182,14 @@ function _to_model(data::_CacheModel; use_nlp_block::Bool)
         end
     end
     MOI.set.(model, MOI.VariablePrimalStart(), x, data.variable_primal)
-    MOI.set(model, MOI.ObjectiveSense(), data.sense)
+    if data.objective != :()
+        MOI.set(model, MOI.ObjectiveSense(), data.sense)
+    end
     if use_nlp_block
         nlp = MOI.Nonlinear.Model()
-        MOI.Nonlinear.set_objective(nlp, data.objective)
+        if data.objective != :()
+            MOI.Nonlinear.set_objective(nlp, data.objective)
+        end
         for (i, expr) in enumerate(data.constraints)
             lb, ub = data.constraint_lower[i], data.constraint_upper[i]
             if lb == ub
@@ -204,8 +208,10 @@ function _to_model(data::_CacheModel; use_nlp_block::Bool)
         block = MOI.NLPBlockData(evaluator)
         MOI.set(model, MOI.NLPBlock(), block)
     else
-        obj = _to_scalar_nonlinear_function(data.objective)
-        MOI.set(model, MOI.ObjectiveFunction{typeof(obj)}(), obj)
+        if data.objective != :()
+            obj = _to_scalar_nonlinear_function(data.objective)
+            MOI.set(model, MOI.ObjectiveFunction{typeof(obj)}(), obj)
+        end
         for (i, expr) in enumerate(data.constraints)
             lb, ub = data.constraint_lower[i], data.constraint_upper[i]
             f = _to_scalar_nonlinear_function(expr)::MOI.ScalarNonlinearFunction

test/FileFormats/NL/data/hs071_no_objective.nl

@@ -0,0 +1,60 @@
+g3 1 1 0
+ 4 2 0 0 1 0
+ 2 0
+ 0 0
+ 4 0 0
+ 0 0 0 1
+ 0 0 0 2 0
+ 8 0
+ 0 0
+ 0 0 0 0 0
+C0
+o2
+v0
+o2
+v2
+o2
+v3
+v1
+C1
+o54
+4
+o5
+v0
+n2
+o5
+v2
+n2
+o5
+v3
+n2
+o5
+v1
+n2
+x4
+0 2.1
+1 2.4
+2 2.2
+3 2.3
+r
+2 25
+4 40
+b
+0 1.1 5.1
+0 1.4 5.4
+0 1.2 1
+0 1.3 5.3
+k3
+2
+4
+6
+J0 4
+0 0
+1 0
+2 0
+3 0
+J1 4
+0 0
+1 0
+2 0
+3 0

test/FileFormats/NL/read.jl

@@ -638,6 +638,16 @@ function test_parse_header_integrality_both_int()
     return
 end
 
+function test_no_objective()
+    model = NL.Model()
+    open(joinpath(@__DIR__, "data", "hs071_no_objective.nl"), "r") do io
+        return read!(io, model)
+    end
+    @test MOI.get(model, MOI.NumberOfVariables()) == 4
+    @test MOI.get(model, MOI.ObjectiveSense()) == MOI.FEASIBILITY_SENSE
+    return
+end
+
 """
     test_mac_minlp()