Consider changing x^1 to return x

[odow]

We currently have these methods:

JuMP.jl/src/operators.jl

Lines 201 to 232 in 8a856bb

	function Base.:^(lhs::AbstractVariableRef, rhs::Integer)
	T = value_type(typeof(lhs))
	if rhs == 2
	return lhs * lhs
	elseif rhs == 1
	return convert(GenericQuadExpr{T,variable_ref_type(lhs)}, lhs)
	elseif rhs == 0
	return one(GenericQuadExpr{T,variable_ref_type(lhs)})
	else
	error(
	"Only exponents of 0, 1, or 2 are currently supported. Are you " *
	"trying to build a nonlinear problem? Make sure you use " *
	"@NLconstraint/@NLobjective.",
	)
	end
	end
	function Base.:^(lhs::GenericAffExpr{T}, rhs::Integer) where {T}
	if rhs == 2
	return lhs * lhs
	elseif rhs == 1
	return convert(GenericQuadExpr{T,variable_ref_type(lhs)}, lhs)
	elseif rhs == 0
	return one(GenericQuadExpr{T,variable_ref_type(lhs)})
	else
	error(
	"Only exponents of 0, 1, or 2 are currently supported. Are you " *
	"trying to build a nonlinear problem? Make sure you use " *
	"@NLconstraint/@NLobjective.",
	)
	end
	end

#3106 will make them somewhat more general by supporting 3+ exponents. In doing so, it makes the return type unstable.

Once merged, we should consider changing x^0 to return one(T) and x^1 to return x.

See also https://github.com/jump-dev/JuMP.jl/pull/3106/files#r1295483658