We compute the ${cal N}=2$ supersymmetric partition function of a gauge theory on a four-dimensional compact toric manifold via equivariant localization. The result is given by a piecewise constant function of the Kahler form with jumps along the walls where the gauge symmetry gets enhanced. The partition function on such manifolds is written as a sum over the residues of a product of partition functions on $mathbb{C}^2$. The evaluation of these residues is greatly simplified by using an abstruse duality that relates the residues at the poles of the one-loop and instanton parts of the $mathbb{C}^2$ partition function. As particular cases, our formulae compute the $SU(2)$ and $SU(3)$ {it equivariant} Donaldson invariants of $mathbb{P}^2$ and $mathbb{F}_n$ and in the non-equivariant limit reproduce the results obtained via wall-crossing and blow up methods in the $SU(2)$ case. Finally, we show that the $U(1)$ self-dual connections induce an anomalous dependence on the gauge coupling, which turns out to satisfy a $mathcal{N}=2$ analog of the $mathcal{N}=4$ holomorphic anomaly equations.
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