[FileFormats.MOF] fix reading nonlinear objectives only (#2068)

Author: odow

src/FileFormats/MOF/read.jl

@@ -30,7 +30,7 @@ function Base.read!(io::IO, model::Model)
 end
 
 function _convert_to_nlpblock(model::Model)
-    has_constraints = false
+    needs_nlp_block = false
     nlp_model = MOI.Nonlinear.Model()
     for S in (
         MOI.LessThan{Float64},
@@ -44,7 +44,7 @@ function _convert_to_nlpblock(model::Model)
             MOI.Nonlinear.add_constraint(nlp_model, f.expr, set)
             # We don't need this in `model` any more.
             MOI.delete(model, ci)
-            has_constraints = true
+            needs_nlp_block = true
         end
     end
     if MOI.get(model, MOI.ObjectiveFunctionType()) == Nonlinear
@@ -58,8 +58,9 @@ function _convert_to_nlpblock(model::Model)
                 0.0,
             ),
         )
+        needs_nlp_block = true
     end
-    if has_constraints
+    if needs_nlp_block
         options = get_options(model)
         evaluator = MOI.Nonlinear.Evaluator(
             nlp_model,

test/FileFormats/MOF/MOF.jl

@@ -1201,6 +1201,35 @@ function test_parse_constraintname_variable()
     return
 end
 
+function test_parse_nonlinear_objective_only()
+    io = IOBuffer()
+    print(
+        io,
+        """{
+    "version": {"major": 1, "minor": 2},
+    "variables": [{"name": "x"}],
+    "objective": {
+        "sense": "min",
+        "function": {
+            "type": "ScalarNonlinearFunction",
+            "root": {"type": "node", "index": 1},
+            "node_list": [{"type": "sin", "args": [{"type": "variable", "name": "x"}]}]
+        }
+    },
+    "constraints": []
+}""",
+    )
+    seekstart(io)
+    model = MOF.Model()
+    read!(io, model)
+    block = MOI.get(model, MOI.NLPBlock())
+    @test block isa MOI.NLPBlockData
+    @test block.has_objective
+    MOI.initialize(block.evaluator, Symbol[])
+    @test MOI.eval_objective(block.evaluator, [2.0]) ≈ sin(2.0)
+    return
+end
+
 function runtests()
     for name in names(@__MODULE__, all = true)
         if startswith("$(name)", "test_")