Error is:
$ zcompile highlighters/main/test-data/function.zsh
zsh: defining function based on alias `ls'
zsh: parse error near `()'
zcompile: can't read file: highlighters/main/test-data/function.zsh
View `Incompatibilities since 5.3.1` in
bb218704d2/README
All these files should be sourced, not executed; and Debian's lintian complains:
W: zsh-syntax-highlighting: script-not-executable usr/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh