\addvspace after a titlesec heading

Question

So, I'm trying to make an environment that is always padded above and below by a certain vertical space, no more and no less (unless the previous or following elements require even more space). My attempt is

\newenvironment{hello}{\addvspace{\baselineskip}}{\addvspace{\baselineskip}}

If I then have two hello environments one after another, then the second \addvspace happily does nothing, as desired. Similarly, after a section title, I get the desired behavior.

\documentclass{article}

\usepackage{lipsum}
%\usepackage{titlesec}
\newenvironment{hello}{\addvspace{\baselineskip}}{\addvspace{\baselineskip}}

\begin{document}

\section{Hellos}
\begin{hello}
    \lipsum[2]
\end{hello}
\begin{hello}
    \lipsum[3]
\end{hello}

\end{document}

But when using titlesec, there is too much space between the section title and the first hello environment. It looks like there's a definite space that goes along with the title that isn't visible to the first \addvspace after it, so \addvspace adds more space.

Any ideas on how to fix this? (Reasons why my entire approach is crappy are also welcome.)

Answer 1

For its spacing, the package titlesec uses \vspace which does not work well with \addvspace. You can use the etoolbox package to patch the internal \ttl@straight@ii command in order to replace the \vspace by a \vskip.

\documentclass{article}

\usepackage{lipsum}
\usepackage{etextools}

\usepackage{titlesec}
\makeatletter
\patchcmd{\ttl@straight@ii}{\vspace{\@tempskipb}}{\vskip \@tempskipb}{}{}
\makeatother

\newenvironment{hello}{\addvspace{\baselineskip}}{\addvspace{\baselineskip}}

\begin{document}

\section{Hellos}
\begin{hello}
    \lipsum[2]
\end{hello}
\begin{hello}
    \lipsum[3]
\end{hello}

\end{document}