Redefine align to include SwapAboveDisplaySkip by default

Question

I have several documents that I am looking to reduce redundant whitespace in and am looking to redefine align to include SwapAboveDisplaySkip from mathtools by default. Since I want to use it almost everywhere, I'd rather not have to manually include it everywhere.

Currently I have the following, which does what I want, except for a new environment rather than for align, which is essentially just the solution from here: Define a custom align, and align* environment

\documentclass{article}
\usepackage{amsmath, mathtools}

\makeatletter
\newenvironment{salign}
{\par\align \SwapAboveDisplaySkip}
{\endalign}
\newenvironment{salign*}
{\par
    \start@align\@ne\st@rredtrue\m@ne}
{\endalign}
\makeatother
\begin{document}

\section{Foo}
\begin{salign}
    a^2+b^2 & = c^2
\end{salign}
\end{document}

I don't want to use this as then I need to define additional files so that the syntax highlighting for my editor works, which means the code won't be portable.

Replacing with renewenvironment creates a recursive loop, I've also tried \let\oldalign\align to fix this, but this doesn't compile.

Answer 1

You can have what you want with \AtBeginEnvironment from etoolbox and \useshortskip from nccmath (to be loaded before mathtools):

\documentclass{article}
\usepackage{nccmath, mathtools}
\usepackage{etoolbox}
\AtBeginEnvironment{align}{\useshortskip}
\AtBeginEnvironment{align*}{\useshortskip}
\begin{document}

\section{Foo}

\noindent\rule\textwidth{0.6pt}
\begin{align*}
    a^2+b^2 & = c^2
\end{align*}
\noindent\rule\textwidth{0.6pt}
\begin{align}
    a^2+b^2 & = c^2
\end{align}
\noindent\rule\textwidth{0.6pt}

\end{document} 

Note: Of course, I tried the same code using \SwapAboveDisplaySkip first, but for some reason, I obtain an error message about a misplaced \noalign. Then I tried \useshortskip, which does essentially the same thing, and it worked.