Unary spacing with unicode-math and hyperref

Question

I'm using LuaLaTeX 1.13.2 from TeX Live 2021, unicode-math 2020-01-31 v0.8q, and hyperref 2021-06-07 v7.00m.

Let's start with

\documentclass{article}
\usepackage[paperwidth=2in, paperheight=1.5in, textwidth=1.5in, textheight=1in]{geometry}
\usepackage{unicode-math}
\pagestyle{empty}
\begin{document}
\begin{equation}
-1
\end{equation}
\begin{equation}
{}-1
\end{equation}
\end{document}

This typesets to the document below; the difference in spacing between the two equations is intended:

Changing the include line to \usepackage{unicode-math,hyperref} messes up the spacing of the unary minus. This affects only the first unary symbol in display math, not if the unary appears in parentheses or inline math:

But changing it to \usepackage{hyperref,unicode-math} inserts additional vertical space between the equations. This is usually not an issue because there should be text between the two equations, but it is still strange:

It seems to be a unicode-math problem because neither issue appears when the package list is a permutation of fontspec and hyperref. The conclusions are unchanged if XeLaTeX is used instead. Are there fixes, and is there a canonical order to include these packages?

Answer 1

You can redefine \incr@eqnum as below. Ulrike and I are considering in chat if this would be safe fix for amsmath to do generally

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

\makeatletter
\def\incr@eqnum{\ifmmode\mathopen\fi{\refstepcounter{equation}}\let\incr@eqnum\@empty}
\makeatother

\pagestyle{empty}
\begin{document}


\begin{equation}
-1
\end{equation}
\begin{equation}
{}-1
\end{equation}
\end{document}