How can I stop this useless empty line popping up in the middle of my lists?

Question

My custom enumerateoptional enumitem environment is putting a useless empty line in the middle of my enumeration list.

To reproduce this, you need to fill a line 100%. See this example I extracted from my full document, reproducing the problem:

\documentclass[12pt]{article}
\errorcontextlines 10000
\usepackage[shortlabels]{enumitem}

\def\renewenumerateoptionalitem{%
  \let\itemenumerateoptional\item%
  \renewcommand{\item}[1][]{%
      \refstepcounter{enumerateoptionali}% increment the counter
      \itemenumerateoptional[\bfseries##1~\theenumerateoptionali]%
  }%
}

\newlist{enumerateoptional}{enumerate}{1}
\setlist[enumerateoptional]{
    before=\renewenumerateoptionalitem,
    label=\arabic*,
    nosep,
    align=left,
    leftmargin=*,
    after=\let\item\itemenumerateoptional,
}

\usepackage{hyperref}
\begin{document}
\begin{enumerateoptional}[1.]
    \item[\bfseries test\_duplicatedContext] Detecção de contextos duplicados e
    emissão de um erro semântico.
    \item[\bfseries test\_duplicatedIncludes] Detecção de inclusões duplicadas  e
    emissão de um erro semântico.
    \item[\bfseries test\_invalidRegexInput] Detecção de expressões regulares 
    inválidas e emissão de um erro semântico.
    \item[\bfseries test\_missingIncludeDetection] Detecção da inclusão um bloco 
    inexistente.
    \item[\bfseries test\_duplicatedGlobalNames] Detecção de múltiplas definições 
    do nome da gramática e
    emissão de um erro semântico.
    \item[\bfseries test\_missingScopeGlobalName] Detecção da falta da definição do 
    nome do escopo global da gramática e emissão de um erro semântico.
\end{enumerateoptional}
\end{document}

---

On the following image, the extra new line is between the 4th and 5th item. It is happening because the 4th line is filled 100% the maximum width and latex is putting a extra new line right after it I do not know why.

How can I stop this useless empty line popping up in the middle of my lists, depending on each item line size?

Answer 1

The blank line you see is a misfeature of your code and hyperref making a PDF destination (when you use \refstepcounter) at that exact point.

The workaround of adding a \par after the text works because the paragraph is built and then the PDF destination is inserted at the beginning of the next line and everything goes well. Adding the PDF destination at the end of the line may cause the destination to go to the next (as far as TeX can see) and then the line seems empty.

An arguably better workaround would be to add \par at the beginning of the definition of your modified \item command, so that you make sure that the PDF destination is inserted in the correct place.

However the correct way would be to attach the destination to the \item itself, so that the PDF destination will always be in the right place. One good bad place to insert it, is right before printing the value of the counter. As Ulrike said in the comment, the label is typeset in a box (by default), and the \@currentlabel is lost (I assumed, incorrectly, that its assignment was global as the counter).

Here's a reworked version which uses a patched version of \@item which uses \refstepcounter in the right place, and uses a few more enumitem

\documentclass[10pt]{article}
\usepackage[shortlabels]{enumitem}
\usepackage{etoolbox}
\makeatletter
\let\user@item\@item
\patchcmd\user@item{\if@noitemarg}{\iftrue}{}{\FAILED}
\enitkv@key{}{formatarg}{\def\enit@format##1{#1}}
% Compatibility with older enumitem.sty:
\@ifundefined{enitkv@enumitem@formatarg}
  {\enitkv@key{enumitem}{formatarg}{\def\enit@format##1{#1}}}{}
\newlist{enumerateoptional}{enumerate}{1}
\setlist[enumerateoptional]{%
    before=\let\@item\user@item,
    formatarg=\textbf{########1~\@itemlabel},
    nosep,
    align=left,
    leftmargin=*,
}
\makeatother
\usepackage[colorlinks]{hyperref}
\begin{document}
\begin{enumerateoptional}[1.]
  \item[test\_duplicatedContext] Detecção de contextos duplicados e
    emissão de um erro semântico.
  \item[test\_duplicatedIncludes] Detecção de inclusões duplicadas  e
    emissão de um erro semântico.
  \item[test\_invalidRegexInput] Detecção de expressões regulares 
    inválidas e emissão de um erro semântico.
  \item[test\_missingIncludeDetection]\label{this} Detecção da inclusão um bloco 
    inexistente.
  \item[test\_duplicatedGlobalNames] Detecção de múltiplas definições 
    do nome da gramática e
    emissão de um erro semântico.
  \item[test\_missingScopeGlobalName] Detecção da falta da definição do 
    nome do escopo global da gramática e emissão de um erro semântico. Ver item~\ref{this}.
\end{enumerateoptional}
\end{document}

Also there is no need to restore \item in the after code (it doesn't harm either) because the \let you do is local to the environment, so once it ends \item is restored to its original definition.

You also don't need \bfseries in every single \item: you already use \bfseries in the new definition of \item.