[breaking] remove fallback for supporting free variables

src/constraints.jl

@@ -1,45 +1,22 @@
-# Constraints
-
 """
-    supports_constraint(model::ModelLike, ::Type{F}, ::Type{S})::Bool where {F<:AbstractFunction,S<:AbstractSet}
+    supports_constraint(
+        model::ModelLike,
+        ::Type{F},
+        ::Type{S},
+    )::Bool where {F<:AbstractFunction,S<:AbstractSet}
 
 Return a `Bool` indicating whether `model` supports `F`-in-`S` constraints, that
 is, `copy_to(model, src)` does not throw [`UnsupportedConstraint`](@ref) when
 `src` contains `F`-in-`S` constraints. If `F`-in-`S` constraints are only not
 supported in specific circumstances, e.g. `F`-in-`S` constraints cannot be
 combined with another type of constraint, it should still return `true`.
-
-    supports_constraint(model::ModelLike, ::Type{VectorOfVariables}, ::Type{Reals})::Bool
-
-Return a `Bool` indicating whether `model` supports free variables. That is,
-`copy_to(model, src)` does not error when `src` contains variables that are not
-constrained by any [`SingleVariable`](@ref) or [`VectorOfVariables`](@ref)
-constraint. By default, this method returns `true` so it should only be
-implemented if `model` does not support free variables. For instance, if a
-solver requires all variables to be nonnegative, it should implement this
-method and return `false` because free variables cannot be copied to the solver.
-
-Note that free variables are not explicitly set to be free by calling
-[`add_constraint`](@ref) with the set [`Reals`](@ref), instead, free variables
-are created with [`add_variable`](@ref) and [`add_variables`](@ref).
-If `model` does not support free variables, it should not implement
-[`add_variable`](@ref) nor [`add_variables`](@ref) but should implement
-this method and return `false`. This allows free variables to be bridged as the
-sum of a nonnegative and a nonpositive variables.
-""" # Implemented as only one method to avoid ambiguity
+"""
 function supports_constraint(
-    model::ModelLike,
-    F::Type{<:AbstractFunction},
-    S::Type{<:AbstractSet},
+    ::ModelLike,
+    ::Type{<:AbstractFunction},
+    ::Type{<:AbstractSet},
 )
-    # TODO remove this condition, as `supports_add_constrained_variables(model, Reals)`
-    # should be called instead of
-    # `supports_constraint(model, ::VectorOfVariables, ::Reals)
-    if F === VectorOfVariables && S === Reals
-        return supports_add_constrained_variables(model, Reals)
-    else
-        return false
-    end
+    return false
 end
 
 """