This question is similar to \eqref in italic math environnment, but I think all the cross referencing tools from
cleveref
justify a separate question.
I would like cleveref
to produce the equation number in a format which is the same as the local environment, namely the italic style in a theorem. The reason I point this out is because other referenced items (like the assumptions) match but the equations don't, and it currently looks inconsistent.
Currently I am using the minimal \crefname{equation}{}{}
as suggested in this answer.
Disclaimer
I realise there is good reason for having \eqref
be upright, but this seems to stem from avoiding strange symbols like & or non-numerical equation labels change drastically between upright and italic. Given I only ever use numeric labels this doesn't seem to apply.
Example
where we can notice the difference between (1)/(1):
MWE
\documentclass{extarticle}
\usepackage{amsmath,amsthm,cleveref,physics}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{assumption}{Assumption}[section]
\Crefname{theorem}{Theorem}{Theorems}
\crefname{equation}{}{} % so cleveref mathes eqref style
\begin{document}
Einstein gave us
\begin{equation}\label{eqt}
e = mc^2.
\end{equation}
\begin{assumption}\label{asmp}
An observer $ S $ measures a velocity $ v $ where $ \abs{v} < c $.
\end{assumption}
\begin{theorem}
\label{thm}
Using \cref{eqt}/(\ref{eqt}) and \Cref{asmp}, the natural choice of metric is $ g_{\mu\nu} = \mathrm{diag}(1,1,1,-1) $.
\end{theorem}
\section{Some comments on \Cref{thm} and \Cref{eqt}} % Some maniac might want to do this....
\end{document}
Extras
If the solution can be clean enough so that it would transfer in environments outside of theorem (e.g. bold) such as sections that would be great. (I can't think of a reason why I would want to do this yet, but anticipate someone else might at a later date).