Restrict what one can do with the OCaml syntax

Until we decide in what direction it should go.

CHANGES.md

@@ -18,6 +18,11 @@
 
 - Deprecate `copy-and-add-line-directive` and rename it `copy#`
 
+- Remove the ability to load arbitrary libraries in jbuild file in
+  OCaml syntax. Only `unix` is supported since a few released packages
+  are using it. The OCaml syntax might eventually be replaced by a
+  simpler mechanism that plays better with incremental builds
+
 - Properly define and implement scopes
 
 - Inside user actions, `${^}` now includes files matches by

ROADMAP.md

@@ -168,23 +168,3 @@ the user can define preferences such as colors.
 It doesn't follow the specification given in the readme of
 [parsexp](https://github.com/janestreet/parsexp). This need to be
 fixed.
-
-## Make Jbuild_plugin a library
-
-Currently Jbuilder generates a wrapper script containing the source
-code of the `Jbuild_plugin` followed by the user script. While this
-method is trivial to implement, it is not great if users want to write
-libraries for jbuild plugins.
-
-What we should do instead is create a proper `jbuild_plugin` library
-that is installed. This library should read a file containing the
-build context details generated by Jbuilder and passed as
-`Sys.argv.(1)`.
-
-We need to refactor things a bit to make this happen, in particular
-the library will propably need to know how to parse s-expression. We
-can create a `jbuild_common` library to put the parts that are common
-between `jbuild_plugin` and `jbuilder`.
-
-Note that `doc/jbuild` is an OCaml script. To simplify the bootstrap,
-we should just convert it back to a static `jbuild` file.

doc/jbuild.rst

@@ -979,28 +979,8 @@ in the rest of this section. The code in the script will have access to a
 <https://github.com/janestreet/jbuilder/blob/master/plugin/jbuild_plugin.mli>`__
 module containing details about the build context it is executed in.
 
-The script can use the directive ``#require`` to access libraries:
-
-.. code:: ocaml
-
-    #require "base,re";;
-
-Note that any library required by a ``jbuild`` file must be part of the
-installed world.
-
-If you don't like the S-expression syntax, then this method gives you a way to
-use whatever else you want. For instance you could have an API to describe your
-project in OCaml directly:
-
-.. code:: ocaml
-
-    (* -*- tuareg -*- *)
-    #require "my_jbuild_api"
-    open My_jbuild_api
-
-    let () =
-      library "foo" ~modules:["plop"; "bidule"]
-
-Currently the ``Jbuild_plugin`` module is only available inside plugins. It is
-however planned to make it a proper library, see `the roadmap
-<../ROADMAP.org>`__ for details.
+The OCaml syntax gives you an escape hatch for when the S-expression
+syntax is not enough. It is not clear whether the OCaml syntax will be
+supported in the long term as it doesn't work well with incremental
+builds. It is possible that it will be replaced by just an ``include``
+stanza where one can include a generated file.

src/jbuild_load.ml

@@ -20,14 +20,35 @@ module Jbuilds = struct
     | Local path -> Path.Local.ensure_parent_directory_exists path
     | External _ -> ()
 
-  let extract_requires str =
-    List.fold_left (String.split str ~on:'\n') ~init:String_set.empty ~f:(fun acc line ->
-      match Scanf.sscanf line "#require %S" (fun x -> x) with
-      | exception _ -> acc
-      | s ->
-        String_set.union acc
-          (String_set.of_list (String.split s ~on:',')))
-    |> String_set.elements
+  let extract_requires ~fname str =
+    let rec loop n lines acc =
+      match lines with
+      | [] -> acc
+      | line :: lines ->
+        let acc =
+          match Scanf.sscanf line "#require %S" (fun x -> x) with
+          | exception _ -> acc
+          | s ->
+            match String.split s ~on:',' with
+            | [] -> acc
+            | ["unix"] as l -> l
+            | _ ->
+              let start =
+                { Lexing.
+                  pos_fname = fname
+                ; pos_lnum  = n
+                ; pos_cnum  = 0
+                ; pos_bol   = 0
+                }
+              in
+              Loc.fail
+                { start; stop = { start with pos_cnum = String.length line } }
+                "Using libraries other that \"unix\" is not supported.\n\
+                 See the manual for details.";
+        in
+        loop (n + 1) lines acc
+    in
+    loop 1 (String.split str ~on:'\n') []
 
   let create_plugin_wrapper (context : Context.t) ~exec_dir ~plugin ~wrapper ~target =
     let plugin = Path.to_string plugin in
@@ -60,7 +81,7 @@ end
                 Printf.sprintf "%-*S , %S" (longest + 2) k v)))
         (Path.reach ~from:exec_dir target)
         plugin plugin_contents);
-    extract_requires plugin_contents
+    extract_requires ~fname:plugin plugin_contents
 
   let eval jbuilds ~(context : Context.t) =
     let open Future in