Avoid line break before acronym

Question

I use the acronym package for acronyms. E.g., I would define a new acronym as \newacro{CDN}{content delivery network} and then use it by writing \ac{CDN}. The first occurrance of this prints: "content delivery network (CDN)"

Sometimes there is a line break before the abbreviation, e.g., after "network" and before "(CDN)". Is there any way to prevent line breaks here? I don't mind line breaks at other positions, e.g., between "content" and "delivery".

I know there are a lot of related questions, but none solves my problem.

Answer 1

The definition of \@acf which prints the acronym as Full (Short) is coded as

\newcommand*{\@acf}[1]{%
\ifAC@footnote
\acsfont{\AC@acs{#1}}%
\footnote{\AC@placelabel{#1}\AC@acl{#1}{}}%
\else
\acffont{%
\AC@placelabel{#1}\AC@acl{#1}%
\nolinebreak[3] %
\acfsfont{(\acsfont{\AC@acs{#1}})}%
}%
\fi
\ifAC@starred\else\AC@logged{#1}\fi}

The \nolinebreak[3] already discourages spacing but does not forbid it (see What is the difference between \nobreak and \nolinebreak?). To forbid breaking, \nolinebreak[4] or simply ~ can be used instead in the definition.

\documentclass{article}
\usepackage{acronym}

\makeatletter
\renewcommand*{\@acf}[1]{%
\ifAC@footnote
\acsfont{\AC@acs{#1}}%
\footnote{\AC@placelabel{#1}\AC@acl{#1}{}}%
\else
\acffont{%
\AC@placelabel{#1}\AC@acl{#1}%
\nolinebreak[3] %
\acfsfont{(\acsfont{\AC@acs{#1}})}%
}%
\fi
\ifAC@starred\else\AC@logged{#1}\fi}
\makeatother

\newacro{PDF}{Portable Document Format}

\begin{document}
Foooooooooooooooooooooooooooooooooooooo \ac{PDF}
\end{document}

Or to follow clemens' approach and do it a little less invasively

\usepackage{etoolbox}
\makeatletter
\patchcmd\@acf
  {\AC@acl{#1}\nolinebreak[3] \acfsfont{(\acsfont{\AC@acs{#1}})}} % search
  {\AC@acl{#1}\nolinebreak[4] \acfsfont{(\acsfont{\AC@acs{#1}})}} % replace
  {} % success
  {} % failure
\makeatother