12. Let the function $f(x)$ be a differentiable function defined on $(-\infty, 0)$, with its derivative being $f^{\prime}(x)$, and it satisfies $2 f(x)+x f^{\prime}(x)>x^{2}$. Then the solution set of the inequality $(x+2017)^{2} f(x+2017)-f(-1)>0$ is $\qquad$ .
Construct the function $g(x)=x^{2} f(x)$, then $g^{\prime}(x)=2 x f(x)+x^{2} f^{\prime}(x)=x\left[2 f(x)+x f^{\prime}(x)\right]g(-1) \Leftrightarrow(x+2017)^{2} f(x+2017)>f(-1) \Rightarrow x+2017<-1 \Rightarrow x<-2018$, so the solution set of the original inequality is $(-\infty,-2018)$.