opam-installed ocamlfind incorrectly finds system installed ocamlfind

install a system compiler and ocamlfind (including findlib dev files, eg libfindlib-ocaml-dev for debian)
create a opam switch using ocaml-system, eval $(opam env)
opam install ocamlfind
ocamlfind query findlib

It will say /usr/lib/x86_64-linux-gnu/ocaml/5.3.0/findlib (or whatever the system path on your os is) instead of /path/to/opam/lib/findlib.

Consequently, programs linking findlib will link the system findlib, and so will not find any opam-installed packages.
For instance opam install rocq-core will fail (eg rocq-prover/rocq#20546).

Considering

ocamlfind/configure

Lines 302 to 310 in bd9aad1

    
           if [ "$ocaml_major" -ge 5 ]; then 
        
               # OCaml 5.0+ installs its own META files under the stdlib directory. 
        
               # If findlib has been configured -sitelib $(ocamlc -where) then there's 
        
               # nothing to do, but otherwise we need to put OCaml's Standard Library 
        
               # into the path setting. 
        
               if [ ! -e "${ocaml_sitelib}/stdlib.cmi" ]; then 
        
                   ocamlpath="${ocaml_core_stdlib}${path_sep}${ocamlpath}" 
        
               fi 
        
           fi

it's possible that this bug only happens with ocaml 5+.

The fix may be as simple as switching the order of paths ie

-        ocamlpath="${ocaml_core_stdlib}${path_sep}${ocamlpath}"
+        ocamlpath="${ocamlpath}${path_sep}${ocaml_core_stdlib}"

but IDK if there are any problems with doing that.

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	if [ "$ocaml_major" -ge 5 ]; then
	# OCaml 5.0+ installs its own META files under the stdlib directory.
	# If findlib has been configured -sitelib $(ocamlc -where) then there's
	# nothing to do, but otherwise we need to put OCaml's Standard Library
	# into the path setting.
	if [ ! -e "${ocaml_sitelib}/stdlib.cmi" ]; then
	ocamlpath="${ocaml_core_stdlib}${path_sep}${ocamlpath}"
	fi
	fi

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