From 1c82406137160f2fa84913144477c98b11c6185b Mon Sep 17 00:00:00 2001
From: Chris Coey <chriscoey@users.noreply.github.com>
Date: Sat, 4 Nov 2023 12:38:54 -0600
Subject: [PATCH] Allow empty array (for no constraints)

---
 src/json_to_moi.jl              | 17 ++++++++---------
 test/all_tests.jl               |  1 +
 test/inputs/empty_arr_con.json  |  1 +
 test/outputs/empty_arr_con.json |  2 ++
 4 files changed, 12 insertions(+), 9 deletions(-)
 create mode 100644 test/inputs/empty_arr_con.json
 create mode 100644 test/outputs/empty_arr_con.json

diff --git a/src/json_to_moi.jl b/src/json_to_moi.jl
index abb5fe5..aca8bfd 100644
--- a/src/json_to_moi.jl
+++ b/src/json_to_moi.jl
@@ -36,17 +36,11 @@ function add_cons!(
     vars_map::Dict,
     solver_info::Dict,
 ) where {T<:Real}
+    isempty(a) && return nothing
     head = a[1]
     if head == "and"
-        for i in eachindex(a)
-            i == 1 && continue
-            if a[i] isa Bool
-                if !a[i]
-                    throw(Error(InvalidModel, "Model is infeasible."))
-                end
-            else
-                add_cons!(T, model, a[i], vars_map, solver_info)
-            end
+        for i in 2:length(a)
+            add_cons!(T, model, a[i], vars_map, solver_info)
         end
     elseif head == "Int"
         v = json_to_snf(a[2], vars_map)
@@ -156,6 +150,11 @@ function add_cons!(
     return nothing
 end
 
+function add_cons!(::Type{<:Real}, ::MOI.ModelLike, a::A, ::Dict, ::Dict) where {A}
+    throw(Error(Unsupported, "Argument $a has type $A but should be a JSON array."))
+    return nothing
+end
+
 _check_v_type(::MOI.VariableIndex) = nothing
 _check_v_type(_) =
     throw(Error(InvalidModel, "$v must be a `MOI.VariableIndex`, not $(typeof(v))."))
diff --git a/test/all_tests.jl b/test/all_tests.jl
index e09a888..9f548d9 100644
--- a/test/all_tests.jl
+++ b/test/all_tests.jl
@@ -76,6 +76,7 @@ end
         "in_con_csp",
         "in_con_const_mip",
         "in_con_expr_csp",
+        "empty_arr_con",
     ]
 
     # solve and check output is expected for each input json file
diff --git a/test/inputs/empty_arr_con.json b/test/inputs/empty_arr_con.json
new file mode 100644
index 0000000..81c78ce
--- /dev/null
+++ b/test/inputs/empty_arr_con.json
@@ -0,0 +1 @@
+{"version":"0.1","sense":"min","variables":["x","y"],"constraints":[[">=","x",1.5],[],["Nonneg","x"],["Nonneg","y"]],"objectives":[["+","x","y"]],"options":{"solver":"HiGHS"}}
diff --git a/test/outputs/empty_arr_con.json b/test/outputs/empty_arr_con.json
new file mode 100644
index 0000000..7ca1c03
--- /dev/null
+++ b/test/outputs/empty_arr_con.json
@@ -0,0 +1,2 @@
+{"termination_status":"OPTIMAL","results":[{"names":["\"x\"","\"y\""],"values":[1.5,0.0],
+"primal_status":"FEASIBLE_POINT","objective_value":1.5}],"version":"0.1"}