Hi,
OCaml 5.2.0 contains ocaml/ocaml#12613 which will make ocamlc and ocamlopt error if no input files are passed.
The configure script relies on this do detect support for -opaque and -g:

Concretely, building findlib in an opam switch before and after the ocaml change yields the following diff:

--- /tmp/opam-good/lib/findlib/Makefile.config
+++ /tmp/opam-bad/lib/findlib/Makefile.config
@@ -24,8 +24,8 @@
 SYSTEM=linux
 NUMTOP=
 SH=
-OPAQUE=-opaque
-OCAMLOPT_G=-g
+OPAQUE=
+OCAMLOPT_G=
 CHECK_BEFORE_INSTALL=0
 INSTALLDIR = install -d
 # change to INSTALLDIR = mkdir -p   when BSD install is unavavailable

This is visible to the end user because linking against findlib will now emit this warning:

Warning 58 [no-cmx-file]: no cmx file was found in path for module Findlib, and its interface was not compiled with -opaque

Thanks