Update

docs/src/manual/nlp.md

@@ -8,6 +8,11 @@ DocTestFilters = [r"≤|<=", r"≥|>=", r" == | = ", r" ∈ | in ", r"MathOptInt
 
 # Nonlinear Modeling
 
+!!! info
+    This page describes the legacy nonlinear interface to JuMP. A new,
+    exerimental nonlinear interface is in development. Find out more by reading
+    [Nonlinear Modeling](@ref new_nonlinear_interface).
+
 JuMP has support for general smooth nonlinear (convex and nonconvex)
 optimization problems. JuMP is able to provide exact, sparse second-order
 derivatives to solvers. This information can improve solver accuracy and

src/optimizer_interface.jl

@@ -415,6 +415,13 @@ function optimize!(
     # The nlp_model is not kept in sync, so re-set it here.
     # TODO: Consider how to handle incremental solves.
     if nonlinear_model(model) !== nothing
+        if _uses_new_nonlinear_interface(model)
+            error(
+                "Cannot optimize a model which contains the features from " *
+                "both the legacy and new nonlinear interfaces. You must use " *
+                "one or the other.",
+            )
+        end
         evaluator = MOI.Nonlinear.Evaluator(
             nonlinear_model(model),
             _differentiation_backend,
@@ -454,6 +461,18 @@ function optimize!(
     return
 end
 
+function _uses_new_nonlinear_interface(model)
+    if objective_function_type(model) <: GenericNonlinearExpr
+        return true
+    end
+    for (F, S) in list_of_constraint_types(model)
+        if F <: GenericNonlinearExpr
+            return true
+        end
+    end
+    return false
+end
+
 """
     compute_conflict!(model::GenericModel)
 

test/test_nlp_expr.jl

@@ -649,4 +649,20 @@ function test_show_nonlinear_model()
     return
 end
 
+function test_error_both_nl_interfaces()
+    model = Model()
+    @variable(model, x)
+    @constraint(model, log(x) <= 1)
+    @NLconstraint(model, log(x) <= 1)
+    @test_throws(
+        ErrorException(
+            "Cannot optimize a model which contains the features from both " *
+            "the legacy and new nonlinear interfaces. You must use one or " *
+            "the other.",
+        ),
+        optimize!(model),
+    )
+    return
+end
+
 end  # module