[Tex/LaTex] Line spacing of chapter headings when using titlesec and setspace packages

Question

I have defined my own chapter heading with modified font size and spacing above and below.

\documentclass[final]{book}
\usepackage{titlesec}
\titleformat{\chapter}[hang]{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter}{0pt}{\LARGE}
\titlespacing*{\chapter}{0pt}{30pt}{20pt}
\def \mychapter#1{\chapter*{#1}}
\begin{document}
\mychapter{Some Very Long Chapter Heading That Will Span Across Two Or More Lines}
\end{document}

Now I am trying to decrease line spacing (baselineskip) for this chapter heading. So I thought setspace package and setstretch command will do the trick.

\documentclass[final]{book}
\usepackage{setspace}
\usepackage{titlesec}
\titleformat{\chapter}[hang]{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter}{0pt}{\LARGE}
\titlespacing*{\chapter}{0pt}{30pt}{20pt}
\def \mychapter#1{\chapter*{\setstretch{0.1}#1}}
\begin{document}
\mychapter{Some Very Long Chapter Heading That Will Span Across Two Or More Lines}
\end{document}

Unfortunately, \setstretch{0.1} seems to have no effect on line spacing. When used on its own, without titlesec package and its commands

\documentclass[final]{book}
\usepackage{setspace}
\def \mychapter#1{\chapter*{\setstretch{0.1}\LARGE#1}}
\begin{document}
\mychapter{Some Very Long Chapter Heading That Will Span Across Two Or More Lines}
\end{document}

it works as expected, but there seems to be some package conflict between titlesec and setspace.

How can I keep my titlesec definition of this chapter heading, but at the same time change (decrease/inrease) its line spacing?

Answer 1

Give the specification in the first mandatory argument (as a personal note, I consider the spacing of your definition a little bit awkward):

\documentclass[final]{book}
\usepackage{setspace}
\usepackage{titlesec}
\titleformat{\chapter}[hang]  
  {\normalfont\huge\bfseries\setstretch{0.1}}
  {\chaptertitlename\ \thechapter}{0pt}{\LARGE}
\titlespacing*{\chapter}{0pt}{30pt}{20pt}

\begin{document}
\chapter{Some Very Long Chapter Heading That Will Span Across Two Or More Lines}
\end{document}

Since, according to comments, no numbering will be used, the following definition would seem the proper way to go (no need for an additional command); I also incorporated barbara beeton's suggestion about suppressing hypheneation in the titles:

\documentclass[final]{book}
\usepackage{setspace}
\usepackage{titlesec}
\titleformat{\chapter}[hang]  
  {\normalfont\filright\bfseries\setstretch{0.1}}
  {}{0pt}{\LARGE}
\titlespacing*{\chapter}{0pt}{30pt}{20pt}

\begin{document}
\chapter{Some Very Long Chapter Heading That Will Span Across Two Or More Lines}
\end{document}