Problem with \hbox inside list

Question

In the example below, the first \hbox to \linewidth ends up at the left of the page, despite the fact that it is inside an itemize environment. The presence of \hspace*{0pt} before the second seems to eliminate the problem.

\documentclass[12pt]{article}
\begin{document}
This is some text which shows the width of the whole page.
We must make sure it is long enough to occupy at least one whole line.
\begin{itemize}
\item 
Inside the itemize environment, the text is not so wide. 
\par
\hbox to \linewidth{\rule{\linewidth}{1pt}}
\par
\hspace*{0pt}\hbox to \linewidth{\rule{\linewidth}{1pt}}
\end{itemize}
\end{document}

What is going on here?

Answer 1

\hbox is not a supported LaTeX command: you are supposed to use \makebox or in this case just \rule directly. (Note similarly that while the LaTeX \rule works the TeX primitive \hrule would fail in the same way as \hbox.

\documentclass[12pt]{article}
\begin{document}
This is some text which shows the width of the whole page.
We must make sure it is long enough to occupy at least one whole line.
\begin{itemize}
\item 
Inside the itemize environment, the text is not so wide. 
\par
\hbox to \linewidth{\rule{\linewidth}{1pt}}
\par
\hspace*{0pt}\hbox to \linewidth{\rule{\linewidth}{1pt}}
\par
\rule{\linewidth}{1pt}
\par
\makebox[\linewidth]{\rule{\linewidth}{1pt}}
\end{itemize}
\end{document}

---

Technically what is going wrong is that LaTeX lists produce indentation by adjusting the paragraph shape, but \hbox does not start a paragraph it adds itself directly to the current vertical or horizontal list, with the result you see.