Add a hook for misses in Load_path

Load_path.find{,_uncap} now invoke a hook before raising Not_found,
which provides a mechanism for automatically adding directories to the
Load_path if required.

10 files changed, 128 insertions, 35 deletions

diff --git a/.depend b/.depend
index 79d4c29b02..57789239b9 100644
--- a/.depend
+++ b/.depend
@@ -6019,6 +6019,7 @@ driver/compmisc.cmx : \
     utils/clflags.cmx \
     driver/compmisc.cmi
 driver/compmisc.cmi : \
+    utils/load_path.cmi \
     typing/env.cmi \
     utils/clflags.cmi
 driver/errors.cmo : \
diff --git a/compilerlibs/Makefile.compilerlibs b/compilerlibs/Makefile.compilerlibs
index 4eb49ca60d..7e044d69be 100644
--- a/compilerlibs/Makefile.compilerlibs
+++ b/compilerlibs/Makefile.compilerlibs
@@ -31,10 +31,10 @@ UTILS = \
   utils/identifiable.cmo \
   utils/numbers.cmo \
   utils/arg_helper.cmo \
-  utils/clflags.cmo \
-  utils/profile.cmo \
   utils/local_store.cmo \
   utils/load_path.cmo \
+  utils/clflags.cmo \
+  utils/profile.cmo \
   utils/terminfo.cmo \
   utils/ccomp.cmo \
   utils/warnings.cmo \
diff --git a/driver/compmisc.ml b/driver/compmisc.ml
index 9e1edd6f40..f3db8728c6 100644
--- a/driver/compmisc.ml
+++ b/driver/compmisc.ml
@@ -13,6 +13,12 @@
 (*                                                                        *)
 (**************************************************************************)
 
+let auto_include find_in_dir fn =
+  if !Clflags.no_std_include then
+    raise Not_found
+  else
+    Load_path.auto_include_otherlibs Location.auto_include_alert find_in_dir fn
+
 (* Initialize the search path.
    [dir] (default: the current directory)
    is always searched first  unless -nocwd is specified,
diff --git a/driver/compmisc.mli b/driver/compmisc.mli
index bb4c292b4f..80394c5eb6 100644
--- a/driver/compmisc.mli
+++ b/driver/compmisc.mli
@@ -21,3 +21,9 @@ val set_from_env : 'a option ref -> 'a Clflags.env_reader -> unit
 val read_clflags_from_env : unit -> unit
 
 val with_ppf_dump : file_prefix:string -> (Format.formatter -> 'a) -> 'a
+
+val auto_include :
+  (Load_path.Dir.t -> string -> string option) -> string -> string
+(** [auto_include find_in_dir fn] is a callback function to be passed to
+    {!Load_path.init} and automatically adds [-I +lib] to the load path after
+    displaying an alert. *)
diff --git a/otherlibs/dynlink/Makefile b/otherlibs/dynlink/Makefile
index 21ed5af164..3a41405c36 100644
--- a/otherlibs/dynlink/Makefile
+++ b/otherlibs/dynlink/Makefile
@@ -79,13 +79,13 @@ COMPILERLIBS_SOURCES=\
   utils/identifiable.ml \
   utils/numbers.ml \
   utils/arg_helper.ml \
+  utils/local_store.ml \
+  utils/load_path.ml \
   utils/clflags.ml \
   utils/profile.ml \
   utils/consistbl.ml \
   utils/terminfo.ml \
   utils/warnings.ml \
-  utils/local_store.ml \
-  utils/load_path.ml \
   utils/int_replace_polymorphic_compare.ml \
   utils/lazy_backtrack.ml \
   parsing/location.ml \
diff --git a/parsing/location.ml b/parsing/location.ml
index d97d43d9c3..0aba4a85ba 100644
--- a/parsing/location.ml
+++ b/parsing/location.ml
@@ -895,6 +895,19 @@ let alert ?(def = none) ?(use = none) ~kind loc message =
 let deprecated ?def ?use loc message =
   alert ?def ?use ~kind:"deprecated" loc message
 
+let auto_include_alert lib =
+  let message = Printf.sprintf "\
+    OCaml's lib directory layout changed in 5.0. The %s subdirectory has been \
+    automatically added to the search path, but you should add -I +%s to the \
+    command-line to silence this alert (e.g. by adding %s to the list of \
+    libraries in your dune file, or adding use_%s to your _tags file for \
+    ocamlbuild, or using -package %s for ocamlfind)." lib lib lib lib lib in
+  let alert =
+    {Warnings.kind="ocaml_deprecated_auto_include"; use=none; def=none;
+     message = Format.asprintf "@[@\n%a@]" Format.pp_print_text message}
+  in
+  prerr_alert none alert
+
 (******************************************************************************)
 (* Reporting errors on exceptions *)
 
diff --git a/parsing/location.mli b/parsing/location.mli
index 5ba80b04da..b33bcdf4b5 100644
--- a/parsing/location.mli
+++ b/parsing/location.mli
@@ -243,6 +243,9 @@ val deprecated: ?def:t -> ?use:t -> t -> string -> unit
 val alert: ?def:t -> ?use:t -> kind:string -> t -> string -> unit
 (** Prints an arbitrary alert. *)
 
+val auto_include_alert: string -> unit
+(** Prints an alert that -I +lib has been automatically added ot the load
+    path *)
 
 (** {1 Reporting errors} *)
 
diff --git a/tools/Makefile b/tools/Makefile
index 66ce89f9cd..afbae6fae3 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -84,8 +84,8 @@ ocamldep.opt$(EXE): $(call byte2native, $(ocamldep_objects))
 # The profiler
 
 OCAMLPROF=config.cmo build_path_prefix_map.cmo misc.cmo identifiable.cmo \
-  numbers.cmo arg_helper.cmo clflags.cmo terminfo.cmo \
-  warnings.cmo location.cmo longident.cmo docstrings.cmo \
+  numbers.cmo arg_helper.cmo local_store.cmo load_path.cmo clflags.cmo \
+  terminfo.cmo warnings.cmo location.cmo longident.cmo docstrings.cmo \
   syntaxerr.cmo ast_helper.cmo \
   camlinternalMenhirLib.cmo parser.cmo \
   pprintast.cmo \
@@ -98,8 +98,8 @@ opt.opt: profiling.cmx
 
 OCAMLCP = config.cmo build_path_prefix_map.cmo misc.cmo profile.cmo \
           warnings.cmo identifiable.cmo numbers.cmo arg_helper.cmo \
-          clflags.cmo local_store.cmo \
-          terminfo.cmo location.cmo load_path.cmo ccomp.cmo compenv.cmo \
+          local_store.cmo load_path.cmo clflags.cmo \
+          terminfo.cmo location.cmo ccomp.cmo compenv.cmo \
           main_args.cmo ocamlcp_common.cmo
 
 ocamlcp$(EXE): $(OCAMLCP) ocamlcp.cmo
@@ -139,8 +139,8 @@ ocamlmklib.opt$(EXE): $(call byte2native, $(OCAMLMKLIB))
 # To make custom toplevels
 
 OCAMLMKTOP=config.cmo build_path_prefix_map.cmo misc.cmo \
-       identifiable.cmo numbers.cmo arg_helper.cmo clflags.cmo \
-       local_store.cmo load_path.cmo profile.cmo ccomp.cmo ocamlmktop.cmo
+       identifiable.cmo numbers.cmo arg_helper.cmo local_store.cmo \
+       load_path.cmo clflags.cmo profile.cmo ccomp.cmo ocamlmktop.cmo
 
 ocamlmktop$(EXE): $(OCAMLMKTOP)
 ocamlmktop.opt$(EXE): $(call byte2native, $(OCAMLMKTOP))
diff --git a/utils/load_path.ml b/utils/load_path.ml
index 2b1d02654b..8873d7b583 100644
--- a/utils/load_path.ml
+++ b/utils/load_path.ml
@@ -31,6 +31,22 @@ module Dir = struct
   let path t = t.path
   let files t = t.files
 
+  let find t fn =
+    if List.mem fn t.files then
+      Some (Filename.concat t.path fn)
+    else
+      None
+
+  let find_uncap t fn =
+    let fn = String.uncapitalize_ascii fn in
+    let search base =
+      if String.uncapitalize_ascii base = fn then
+        Some (Filename.concat t.path base)
+      else
+        None
+    in
+    List.find_map search t.files
+
   (* For backward compatibility reason, simulate the behavior of
      [Misc.find_in_path]: silently ignore directories that don't exist
      + treat [""] as the current directory. *)
@@ -45,12 +61,15 @@ module Dir = struct
 end
 
 let dirs = s_ref []
+let default_auto_include_callback _ _ = raise Not_found
+let auto_include_callback = ref default_auto_include_callback
 
 let reset () =
   assert (not Config.merlin || Local_store.is_bound ());
   STbl.clear !files;
   STbl.clear !files_uncap;
-  dirs := []
+  dirs := [];
+  auto_include_callback := default_auto_include_callback
 
 let get () = List.rev !dirs
 let get_paths () = List.rev_map Dir.path !dirs
@@ -66,10 +85,11 @@ let prepend_add dir =
       STbl.replace !files_uncap (String.uncapitalize_ascii base) fn
     ) dir.Dir.files
 
-let init l =
+let init ?(auto_include=default_auto_include_callback) l =
   reset ();
   dirs := List.rev_map Dir.create l;
-  List.iter prepend_add !dirs
+  List.iter prepend_add !dirs;
+  auto_include_callback := auto_include
 
 let remove_dir dir =
   assert (not Config.merlin || Local_store.is_bound ());
@@ -109,16 +129,45 @@ let prepend_dir dir =
 
 let is_basename fn = Filename.basename fn = fn
 
+let auto_include_libs libs alert find_in_dir fn =
+  let scan (lib, lazy dir) =
+    let file = find_in_dir dir fn in
+    let alert_and_add_dir _ =
+      alert lib;
+      append_dir dir
+    in
+    Option.iter alert_and_add_dir file;
+    file
+  in
+  match List.find_map scan libs with
+  | Some base -> base
+  | None -> raise Not_found
+
+let auto_include_otherlibs =
+  (* Ensure directories are only ever scanned once *)
+  let expand = Misc.expand_directory Config.standard_library in
+  let otherlibs =
+    let read_lib lib = lazy (Dir.create (expand ("+" ^ lib))) in
+    List.map (fun lib -> (lib, read_lib lib)) ["dynlink"; "str"; "unix"] in
+  auto_include_libs otherlibs
+
 let find fn =
   assert (not Config.merlin || Local_store.is_bound ());
-  if is_basename fn && not !Sys.interactive then
-    STbl.find !files fn
-  else
-    Misc.find_in_path (get_paths ()) fn
+  try
+    if is_basename fn && not !Sys.interactive then
+      STbl.find !files fn
+    else
+      Misc.find_in_path (get_paths ()) fn
+  with Not_found ->
+    !auto_include_callback Dir.find fn
 
 let find_uncap fn =
   assert (not Config.merlin || Local_store.is_bound ());
-  if is_basename fn && not !Sys.interactive then
-    STbl.find !files_uncap (String.uncapitalize_ascii fn)
-  else
-    Misc.find_in_path_uncap (get_paths ()) fn
+  try
+    if is_basename fn && not !Sys.interactive then
+      STbl.find !files_uncap (String.uncapitalize_ascii fn)
+    else
+      Misc.find_in_path_uncap (get_paths ()) fn
+  with Not_found ->
+    let fn_uncap = String.uncapitalize_ascii fn in
+    !auto_include_callback Dir.find_uncap fn_uncap
diff --git a/utils/load_path.mli b/utils/load_path.mli
index 1f9aba28bf..570f477701 100644
--- a/utils/load_path.mli
+++ b/utils/load_path.mli
@@ -31,9 +31,37 @@ val remove_dir : string -> unit
 val reset : unit -> unit
 (** Remove all directories *)
 
-val init : string list -> unit
+module Dir : sig
+  type t
+  (** Represent one directory in the load path. *)
+
+  val create : string -> t
+
+  val path : t -> string
+
+  val files : t -> string list
+  (** All the files in that directory. This doesn't include files in
+      sub-directories of this directory. *)
+
+  val find : t -> string -> string option
+  (** [find dir fn] returns the full path to [fn] in [dir]. *)
+
+  val find_uncap : t -> string -> string option
+  (** As {!find}, but search also for uncapitalized name, i.e. if name is
+      Foo.ml, either /path/Foo.ml or /path/foo.ml may be returned. *)
+end
+
+val init :
+  ?auto_include:((Dir.t -> string -> string option) -> string -> string) ->
+  string list -> unit
 (** [init l] is the same as [reset (); List.iter add_dir (List.rev l)] *)
 
+val auto_include_otherlibs :
+  (string -> unit) -> (Dir.t -> string -> string option) -> string -> string
+(** [auto_include_otherlibs alert] is a callback function to be passed to
+    {!Load_path.init} and automatically adds [-I +lib] to the load path after
+    calling [alert lib]. *)
+
 val get_paths : unit -> string list
 (** Return the list of directories passed to [add_dir] so far. *)
 
@@ -47,19 +75,6 @@ val find_uncap : string -> string
 (** Same as [find], but search also for uncapitalized name, i.e.  if
     name is Foo.ml, allow /path/Foo.ml and /path/foo.ml to match. *)
 
-module Dir : sig
-  type t
-  (** Represent one directory in the load path. *)
-
-  val create : string -> t
-
-  val path : t -> string
-
-  val files : t -> string list
-  (** All the files in that directory. This doesn't include files in
-      sub-directories of this directory. *)
-end
-
 val[@deprecated] add : Dir.t -> unit
 (** Old name for {!append_dir} *)