From cdd43162040421eb9c2a002707e91510adbfbe41 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Legat?= <benoit.legat@gmail.com>
Date: Mon, 10 May 2021 07:42:20 -0400
Subject: [PATCH 1/2] Add throw_if_scalar_and_constant_not_zero

---
 src/Bridges/bridge_optimizer.jl | 21 ++++-----------------
 src/constraints.jl              | 29 +++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/src/Bridges/bridge_optimizer.jl b/src/Bridges/bridge_optimizer.jl
index 417c3a2b96..8277799b49 100644
--- a/src/Bridges/bridge_optimizer.jl
+++ b/src/Bridges/bridge_optimizer.jl
@@ -1742,23 +1742,10 @@ function bridged_constraint_function(
     if !Variable.has_bridges(Variable.bridges(b))
         return func, set
     end
-    if func isa MOI.AbstractScalarFunction
-        constant = MOI.constant(func)
-        if !iszero(constant)
-            # We use the fact that the initial function constant was zero to
-            # implement getters for `MOI.ConstraintFunction` and
-            # `MOI.ConstraintSet`. See `unbridged_constraint_function`.
-            throw(
-                MOI.ScalarFunctionConstantNotZero{
-                    typeof(constant),
-                    typeof(func),
-                    typeof(set),
-                }(
-                    constant,
-                ),
-            )
-        end
-    end
+    # We use the fact that the initial function constant was zero to
+    # implement getters for `MOI.ConstraintFunction` and
+    # `MOI.ConstraintSet`. See `unbridged_constraint_function`.
+    MOI.throw_if_scalar_and_constant_not_zero(func, typeof(set))
     f = bridged_function(b, func)::typeof(func)
     return MOIU.normalize_constant(f, set)
 end
diff --git a/src/constraints.jl b/src/constraints.jl
index 5867828021..47099cff76 100644
--- a/src/constraints.jl
+++ b/src/constraints.jl
@@ -103,6 +103,35 @@ function Base.showerror(
     )
 end
 
+"""
+    throw_if_scalar_and_constant_not_zero(func, S::Type)
+
+Throw a `ScalarFunctionConstantNotZero(index)` error `func` is a scalar function
+whose constant is not zero.
+"""
+function throw_if_scalar_and_constant_not_zero(
+    func::AbstractScalarFunction,
+    ::Type{S},
+) where {S<:AbstractScalarSet}
+    cst = constant(func)
+    if !iszero(cst)
+        throw(ScalarFunctionConstantNotZero{typeof(cst),typeof(func),S}(cst))
+    end
+    return
+end
+function throw_if_scalar_and_constant_not_zero(
+    ::SingleVariable,
+    ::Type{S},
+) where {S<:AbstractScalarSet}
+    return
+end
+function throw_if_scalar_and_constant_not_zero(
+    ::AbstractVectorFunction,
+    ::Type{S},
+) where {S<:AbstractVectorSet}
+    return
+end
+
 """
     add_constraint(model::ModelLike, func::F, set::S)::ConstraintIndex{F,S} where {F,S}
 

From 36de969f55af3b318561b7d866e09f7aa6475a37 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Legat?= <benoit.legat@gmail.com>
Date: Mon, 10 May 2021 23:37:46 -0400
Subject: [PATCH 2/2] Add tests

---
 test/constraints.jl | 23 +++++++++++++++++++++++
 test/runtests.jl    |  1 +
 2 files changed, 24 insertions(+)
 create mode 100644 test/constraints.jl

diff --git a/test/constraints.jl b/test/constraints.jl
new file mode 100644
index 0000000000..0cd16f4c66
--- /dev/null
+++ b/test/constraints.jl
@@ -0,0 +1,23 @@
+using Test
+using MathOptInterface
+const MOI = MathOptInterface
+
+function constant_not_zero_test(::Type{T}) where {T}
+    S = MOI.EqualTo{T}
+    x = MOI.VariableIndex(1)
+    fx = MOI.SingleVariable(x)
+    @test nothing === MOI.throw_if_scalar_and_constant_not_zero(fx, S)
+    func1 = one(T) * fx + one(T)
+    @test_throws MOI.ScalarFunctionConstantNotZero begin
+        MOI.throw_if_scalar_and_constant_not_zero(func1, S)
+    end
+    func2 = one(T) * fx
+    @test nothing === MOI.throw_if_scalar_and_constant_not_zero(func2, S)
+    func = MOI.Utilities.operate(vcat, T, func1, func2)
+    @test nothing === MOI.throw_if_scalar_and_constant_not_zero(func, MOI.Zeros)
+end
+
+@testset "Constant not zero" begin
+    constant_not_zero_test(Int)
+    constant_not_zero_test(Float64)
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 9d9a8b6b30..0eb42c20b1 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -22,6 +22,7 @@ include("dummy.jl")
     include("functions.jl")
     include("sets.jl")
     include("attributes.jl")
+    include("constraints.jl")
     include("instantiate.jl")
     include("deprecate.jl")
 end