Add another method

Author: odow

src/Utilities/promote_operation.jl

@@ -24,9 +24,10 @@ There are five methods for which we implement `Utilities.promote_operation`:
     c. `promote_operation(::typeof(-), ::Type{T}, ::Type{F1}, ::Type{Vector{T}})`
  3. `*`
     a. `promote_operation(::typeof(*), ::Type{T}, ::Type{T}, ::Type{F})`
-    b. `promote_operation(::typeof(*), ::Type{T}, ::Type{F1}, ::Type{F2})`
+    b. `promote_operation(::typeof(*), ::Type{T}, ::Type{T}, ::Type{F})`
+    c. `promote_operation(::typeof(*), ::Type{T}, ::Type{F1}, ::Type{F2})`
        where `F1` and `F2` are `VariableIndex` or `ScalarAffineFunction`
-    c. `promote_operation(::typeof(*), ::Type{T}, ::Type{<:Diagonal{T}}, ::Type{F}`
+    d. `promote_operation(::typeof(*), ::Type{T}, ::Type{<:Diagonal{T}}, ::Type{F}`
  4. `/`
     a. `promote_operation(::typeof(/), ::Type{T}, ::Type{F}, ::Type{T})`
  5. `vcat`
@@ -243,6 +244,46 @@ end
 
 ### Method 3b
 
+function promote_operation(
+    ::typeof(*),
+    ::Type{T},
+    ::Type{F},
+    ::Type{T},
+) where {
+    T,
+    F<:Union{
+        # T,  # Stackoverflow if included
+        MOI.ScalarAffineFunction{T},
+        MOI.ScalarQuadraticFunction{T},
+        MOI.ScalarNonlinearFunction,
+        AbstractVector{T},
+        MOI.VectorAffineFunction{T},
+        MOI.VectorQuadraticFunction{T},
+    },
+}
+    return F
+end
+
+function promote_operation(
+    ::typeof(*),
+    ::Type{T},
+    ::Type{MOI.VariableIndex},
+    ::Type{T},
+) where {T}
+    return MOI.ScalarAffineFunction{T}
+end
+
+function promote_operation(
+    ::typeof(*),
+    ::Type{T},
+    ::Type{MOI.VectorOfVariables},
+    ::Type{T},
+) where {T}
+    return MOI.VectorAffineFunction{T}
+end
+
+### Method 3c
+
 function promote_operation(
     ::typeof(*),
     ::Type{T},
@@ -252,7 +293,7 @@ function promote_operation(
     return MOI.ScalarQuadraticFunction{T}
 end
 
-### Method 3c
+### Method 3d
 
 function promote_operation(
     ::typeof(*),

test/Utilities/test_promote_operation.jl

@@ -143,6 +143,27 @@ function test_promote_operation_3a()
     return
 end
 
+function test_promote_operation_3b()
+    T = Int
+    F = (
+        T,
+        MOI.VariableIndex,
+        MOI.ScalarAffineFunction{T},
+        MOI.ScalarQuadraticFunction{T},
+        MOI.ScalarNonlinearFunction,
+        Vector{T},
+        MOI.VectorOfVariables,
+        MOI.VectorAffineFunction{T},
+        MOI.VectorQuadraticFunction{T},
+    )
+    special_cases = Dict(2 => 3, 7 => 8)
+    for i in 1:9
+        j = get(special_cases, i, i)
+        @test MOI.Utilities.promote_operation(*, T, F[i], T) == F[j]
+    end
+    return
+end
+
 function test_promote_operation_4a()
     T = Int
     F = (