Fix StackOverflowError coming from MOI.Utilities.operate

Project.toml

@@ -5,12 +5,13 @@ version = "0.1.0"
 [deps]
 JSON3 = "0f8b85d8-7281-11e9-16c2-39a750bddbf1"
 MathOptInterface = "b8f27783-ece8-5eb3-8dc8-9495eed66fee"
+MutableArithmetics = "d8a4904e-b15c-11e9-3269-09a3773c0cb0"
 
 [compat]
-ReTestItems = "1"
-julia = "1.8"
 JSON3 = "1"
 MathOptInterface = "1"
+ReTestItems = "1"
+julia = "1.8"
 
 [extras]
 Coverage = "a2441757-f6aa-5fb2-8edb-039e3f45d037"

src/SolverAPI.jl

@@ -11,6 +11,7 @@ module SolverAPI
 
 import MathOptInterface as MOI
 import JSON3
+import MutableArithmetics as MA
 
 export serialize, deserialize, solve, print_model, response
 
@@ -469,8 +470,20 @@ function nl_to_aff_or_quad(::Type{T}, f::MOI.ScalarNonlinearFunction) where {T<:
                 return MOI.Utilities.operate(*, T, args[1], args[1])
             end
         else
-            h = get(_quad_ops, f.head, nothing)
-            isnothing(h) || return MOI.Utilities.operate(h, T, args...)
+            if f.head == :+
+                # TODO (dba) this is a workaround to avoid a
+                # `StackOverflowError` error coming from
+                # `MOI.Utilities.operate`. We should avoid the `...`
+                # all together.
+                if args isa Vector{MOI.ScalarAffineFunction{Float64}}
+                    return MA.operate!(+, args[1], args[2...])
+                else
+                    return MOI.Utilities.operate(+, T, args...)
+                end
+            else
+                h = get(_quad_ops, f.head, nothing)
+                isnothing(h) || return MOI.Utilities.operate(h, T, args...)
+            end
         end
     end
     throw(Error(Domain, "Function $f cannot be converted to linear or quadratic form."))

test/solve_tests.jl

@@ -9,9 +9,10 @@ import MathOptInterface as MOI
 export run_solve, read_json
 
 function _get_solver(solver_name::String)
-    if solver_name == "MiniZinc"
+    solver_name_lower = lowercase(solver_name)
+    if solver_name_lower == "minizinc"
         return MiniZinc.Optimizer{Int}("chuffed")
-    elseif solver_name == "HiGHS"
+    elseif solver_name_lower == "highs"
         return HiGHS.Optimizer()
     else
         error("Solver $solver_name not supported.")
@@ -102,3 +103,19 @@ end
         @test length(errors) >= 1
     end
 end
+
+@testitem "stress-test" setup = [SolverSetup] begin
+    using SolverAPI
+    import JSON3
+
+    # names of JSON files in inputs/ and outputs/ folders
+    json_names = [
+        "nl_to_aff_or_quad_overflow", # This has 110000 constraints and 100000 variables.
+    ]
+
+    @testset "$j" for j in json_names
+        input = read_json("inputs", j)
+        output = JSON3.read(run_solve(input))
+        @test output isa JSON3.Object
+    end
+end