[install] dune install seems to lack enough configuration options as to accommodate Linux's FSH

[ejgallego]

Hi folks,

we got some reports of dune-built packages installing incorrectly in Debian, and indeed, if we look at the code, we have:

dune/src/dune_engine/install.ml

Lines 146 to 167 in 6698257

	let make ~package ~destdir ?(libdir = Path.relative destdir "lib")
	?(mandir = Path.relative destdir "man") () =
	let package = Package.Name.to_string package in
	let lib_root = libdir in
	let libexec_root = libdir in
	let share_root = Path.relative destdir "share" in
	let etc_root = Path.relative destdir "etc" in
	let doc_root = Path.relative destdir "doc" in
	{ lib_root
	; libexec_root
	; share_root
	; bin = Path.relative destdir "bin"
	; sbin = Path.relative destdir "sbin"
	; man = mandir
	; toplevel = Path.relative libdir "toplevel"
	; stublibs = Path.relative libdir "stublibs"
	; lib = Path.relative lib_root package
	; libexec = Path.relative libexec_root package
	; share = Path.relative share_root package
	; etc = Path.relative etc_root package
	; doc = Path.relative doc_root package
	}

which is incorrect for example for (section doc) , as it will install in /usr/doc whereas Debian specifies /usr/share/doc

What should we do here? Should we just add a --docdir option in the same way opam-installer does support it?

cc: @JasonGross

[bobot]

Yes in #680 it was proposed to have the same variable than autoconf. I will look at that this afternoon together with #3978