"Module is unavailable" error, when using new -I +str syntax [SOLVED]

Learning
1

I recently switched from a <5 OCaml compiler to a 5.1.1 version.
I therefore need to take the following warning from ocamlc into account :

File "_none_", line 1:
Alert ocaml_deprecated_auto_include: 
OCaml's lib directory layout changed in 5.0. The str subdirectory has been
automatically added to the search path, but you should add -I +str to the
command-line to silence this alert (e.g. by adding str to the list of
libraries in your dune file, or adding use_str to your _tags file for
ocamlbuild, or using -package str for ocamlfind).

To consider a minimal example, suppose we have just one file using_str.ml
which contains just the line let bs = Str.bounded_split ;;

My naive try at the new syntax works with partial, separate compilation (with the “-c” option)
but not with full compilation (without the “-c” option) :

$ls
using_str.ml
$ocamlc -I +str -c using_str.ml
$ls
using_str.cmi  using_str.cmo  using_str.ml
$ocamlc -I +str  using_str.ml
File "using_str.ml", line 1:
Error: Module `Str' is unavailable (required by `Using_str')

What is the correct syntax for the second call to ocamlc ?

Unless I missed something, this error “Module (…) is unavailable” is not documented
in the OCaml manual. Section 13.4 only lists the most common errors which do not include this one.

2

When linking, you need to provide the archives of the linked libraries:

$ ocamlc -I +str -c using_str.ml
$ ocamlc -I +str str.cma using_str.cmo -o using_str

or in one command:

$ ocamlc -I +str str.cma using_str.ml -o using_str
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