Throw error for add_to_expression with GenericNonlinearExpr

src/nlp_expr.jl

@@ -1144,3 +1144,12 @@ end
 function LinearAlgebra.qr(::AbstractMatrix{<:AbstractJuMPScalar})
     return throw(MOI.UnsupportedNonlinearOperator(:qr))
 end
+
+function add_to_expression!(f::GenericNonlinearExpr, args...)
+    return error(
+        "`add_to_expression!` is not supported for expressions of type " *
+        "`$(typeof(f))` because they cannot be modified in-place. " *
+        "Instead of `add_to_expression!(expr, args..)`, use " *
+        "`expr += *(args...)`.",
+    )
+end

test/test_nlp_expr.jl

@@ -926,4 +926,20 @@ function test_generic_nonlinear_expr_infer_variable_type()
     return
 end
 
+function test_add_to_expression!()
+    model = Model()
+    @variable(model, x)
+    y = zero(NonlinearExpr)
+    @test_throws(
+        ErrorException(
+            "`add_to_expression!` is not supported for expressions of type " *
+            "`$(typeof(y))` because they cannot be modified in-place. " *
+            "Instead of `add_to_expression!(expr, args..)`, use " *
+            "`expr += *(args...)`.",
+        ),
+        test_add_to_expression!(y, 2.0, sin(x)),
+    )
+    return
+end
+
 end  # module