Create a left-aligned roman numeral list with labelsep that is invariant of label width

Question

I want a list with left margin equal to \parindent, and every list starting with an indent equal to \parindent i.e., the first item would be indented by twice \parindent. Moreover, the list will be left-aligned and in roman numerals surrounded by bracket.

My MWE is the following:

\documentclass{article}
\usepackage{enumitem}

\setlist{leftmargin=\parindent,
itemindent=\dimexpr\labelwidth+\labelsep+\parindent,
align=left,nosep,
listparindent=\parindent,
label={({\itshape\roman*}\,)},
labelsep=0pt}

\begin{document}

\section{First section}

Text before list, first paragraph. The sentence in first paragraph is The quick brown fox jumps over the lazy dog.

Text before list, second paragraph. The sentence in second paragraph is alpha beta gamma delta epsilon zeta eta omega.

\begin{enumerate}
    \item The first item first line. The sentence in first item is The quick brown fox jumps over the lazy dog.
    \item The second item first line. The sentence in second item is alpha beta gamma delta epsilon zeta eta omega.
\end{enumerate}

Text after list, first paragraph. The sentence in first paragraph is The quick brown fox jumps over the lazy dog.


\end{document}

which leads to the following output:

Everything is all well and good, except for the separation between the closing bracket and the item content. The first item clearly has a larger gap. I guess this is done to make up for the fact that items have varying label width. This difference in gap is more pronounced in the third since (iii) would be even wider (not shown here). I want all items to be separated a constant distance from the item label.

I tried label=\mbox{({\itshape\roman*}\,)} to no avail.

(EDIT)
What I want:

(EDIT 2)
Strangely enough, fbox seems to do what I want (except for the box). I thought mbox and fbox should behave the same way aside from the box.

Answer 1

I'm not sure you want to set all lists this way, so I propose a new list. You're free to use it for every list, but…

\documentclass{article}
\usepackage{enumitem}

\newlist{roster}{enumerate}{1}
\setlist[roster]{
  leftmargin=\parindent,
  labelwidth=0pt,
  itemindent=\dimexpr 0.5em+\parindent\relax,
  align=left,
  nosep,
  listparindent=\parindent,
  label={({\itshape\roman*}\,)},
  labelsep=0.5em,
}

\begin{document}

\section{First section}

Text before list, first paragraph. The sentence in first paragraph is 
The quick brown fox jumps over the lazy dog.

\hspace*{\parindent}Check double parindent

\begin{roster}
    \item The first item first line. The sentence in first item is 
          The quick brown fox jumps over the lazy dog.
    \item The second item first line. The sentence in second item is
          alpha beta gamma delta epsilon zeta eta omega.
\end{roster}

Text after list, first paragraph. The sentence in first paragraph is The quick brown fox jumps over the lazy dog.


\end{document}

The trick is to set the label width to zero and the item indent to the \parindent plus the label sep.

Sorry, but I don't find this very attractive.