[Tex/LaTex] Bump right-aligned text to next line if no room

Question

I'm trying to write a simple command that will put some text right-aligned, but bump it to the next line if it doesn't fit well. Since an image is worth a thousand words:

The "Normally" case is correct – that's what it should do. But if the line gets too long, I'd like it to bump to the next line, as shown in "Desired". Currently, what I have does "Failure". Here's what I've come up with so far:

\newcommand{\when}[1]{\hfill\mbox{\textit{#1}}}

Note: I had to manually push the "Desired" to the right with a \\ \strut, but I'd like the macro to automate this, and to not have to pick out the cases where I need to do that by hand. (Simply adding \\ \strut to the macro results in the wrong output for the "Normally" case.)

Answer 1

There are some cases where both Herbert's and Thorsten Donig's answers can be problematic. One situation is when the stuff at the end needs a new line, but that line also starts a new page. This makes an especially awkward widow, since it would start a page flushed right. The other potential problem involves hyphenation. Herbert's solution does not work properly on lines that are started by hyphenated words (it starts a new line even if there is enough space to flush right), and Thorsten Donig's solution seems to break hyphenation of the preceding word.

\documentclass{article}
\usepackage[papersize={10cm,5cm},textwidth=5cm,vmargin=5mm]{geometry}
\usepackage{calc,parskip}
\newcommand{\atend}{\makebox[2em][l]{\leaders\hbox{b}\hfill}}
\newcommand{\fillpage}{\vspace*{\textheight}\vspace*{-2\baselineskip}\vspace{-\parskip}}
\overfullrule=2pt
\pagestyle{empty}

\begin{document}
\fillpage

\newcommand\comfyfill[1]{{% = Herbert's \When
  \leftskip=0ptplus1fil\rightskip=-\leftskip\parfillskip=\leftskip
  \hfill \phantom{ } \textit{\mbox{#1}}\par}}

\makebox[\textwidth-2em]{\hrulefill a}\comfyfill{\atend}

\makebox[\textwidth-\widthof{charac- }]{\hrulefill} characterisation \comfyfill{\atend}

\makebox[\textwidth-\widthof{charac- }]{\hrulefill} charac- terisation \comfyfill{\atend}

\newpage
\fillpage

\renewcommand*{\comfyfill}[1]{% = Thorsten Donig's \signed
  \unskip\hspace*{1em plus 1fill}
  \nolinebreak[3]%
  \hspace*{\fill}\mbox{\emph{#1}}
  \parfillskip0pt\par
}

\makebox[\textwidth-2em]{\hrulefill a}\comfyfill{\atend}

\makebox[\textwidth-\widthof{charac- }]{\hrulefill} characterisation \comfyfill{\atend}

\makebox[\textwidth-\widthof{charac- }]{\hrulefill} charac- terisation \comfyfill{\atend}

\end{document}

Here is the output from Herbert's solution:

An here is the output from Thorsten Donig's: