Line width in parshape environment

Question

I would like to get the current line width in a \parshape environment.

The following variables return the full page width (345pt), where I would expect 300pt:

\documentclass{report}

\usepackage{lipsum}

\begin{document} 

\parshape=5
0pt 300pt
0pt 300pt
0pt 300pt
0pt 300pt
0pt 300pt
\noindent\the\textwidth\\ \the\linewidth\\ \the\columnwidth\\ \the\hsize\\\lipsum[1]

\end{document}

How can I get the expected (size) value?

Answer 1

You may use the e-TeX provided primitives¹

\parshapeindent
\parshapelength,

each of them followed by an integer, to access the indent and length of lines under the current \parshape specification, but it's impossible to know what's the line length or indent pertaining to the line where a word will appear, because that's decided on much later, when TeX has applied its algorithm for splitting the paragraph into lines. In other words, there's no notion of “the current line”. Examples can be made of paragraphs where changing one word can lead to largely different line breaks.

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¹ e-TeX extensions are available when LaTeX is used (at least on TeX system releases from about 2004 on).