Implements custom resolvers

src/commands/commandUtils.ml

@@ -786,6 +786,7 @@ let make_options ~flowconfig ~lazy_mode ~root (options_flags: Options_flags.t) =
     opt_profile = options_flags.profile;
     opt_strip_root = options_flags.strip_root;
     opt_module = FlowConfig.module_system flowconfig;
+    opt_module_resolver = FlowConfig.module_resolver flowconfig;
     opt_munge_underscores =
       options_flags.munge_underscore_members || FlowConfig.munge_underscores flowconfig;
     opt_temp_dir = temp_dir;

src/commands/config/flowConfig.ml

@@ -49,6 +49,7 @@ module Opts = struct
     haste_use_name_reducers: bool;
     ignore_non_literal_requires: bool;
     include_warnings: bool;
+    module_resolver: Path.t option;
     module_system: Options.module_system;
     module_name_mappers: (Str.regexp * string) list;
     node_resolver_dirnames: string list;
@@ -154,6 +155,7 @@ module Opts = struct
     ignore_non_literal_requires = false;
     include_warnings = false;
     merge_timeout = Some 100;
+    module_resolver = None;
     module_system = Options.Node;
     module_name_mappers = [];
     node_resolver_dirnames = ["node_modules"];
@@ -677,6 +679,15 @@ let parse_options config lines =
       );
     }
 
+    |> define_opt "module.resolver" {
+      initializer_ = USE_DEFAULT;
+      flags = [];
+      optparser = optparse_filepath;
+      setter = (fun opts v -> Ok {
+        opts with module_resolver = Some v;
+      });
+    }
+
     |> define_opt "module.system" {
       initializer_ = USE_DEFAULT;
       flags = [];
@@ -1019,6 +1030,7 @@ let max_workers c = c.options.Opts.max_workers
 let merge_timeout c = c.options.Opts.merge_timeout
 let module_file_exts c = c.options.Opts.module_file_exts
 let module_name_mappers c = c.options.Opts.module_name_mappers
+let module_resolver c = c.options.Opts.module_resolver
 let module_resource_exts c = c.options.Opts.module_resource_exts
 let module_system c = c.options.Opts.module_system
 let modules_are_use_strict c = c.options.Opts.modules_are_use_strict

src/commands/config/flowConfig.mli

@@ -57,6 +57,7 @@ val max_workers: config -> int
 val merge_timeout: config -> int option
 val module_file_exts: config -> SSet.t
 val module_name_mappers: config -> (Str.regexp * string) list
+val module_resolver: config -> Path.t option
 val module_resource_exts: config -> SSet.t
 val module_system: config -> Options.module_system
 val modules_are_use_strict: config -> bool

src/common/options.ml

@@ -63,6 +63,7 @@ type t = {
   opt_merge_timeout: float option;
   opt_module: module_system;
   opt_module_name_mappers: (Str.regexp * string) list;
+  opt_module_resolver: Path.t option;
   opt_modules_are_use_strict: bool;
   opt_munge_underscores: bool;
   opt_profile : bool;
@@ -107,6 +108,7 @@ let max_trace_depth opts = opts.opt_traces
 let max_workers opts = opts.opt_max_workers
 let merge_timeout opts = opts.opt_merge_timeout
 let module_name_mappers opts = opts.opt_module_name_mappers
+let module_resolver opts = opts.opt_module_resolver
 let module_system opts = opts.opt_module
 let modules_are_use_strict opts = opts.opt_modules_are_use_strict
 let root opts = opts.opt_root

src/services/inference/module_js.ml

@@ -304,6 +304,45 @@ let eponymous_module file =
 
 (*******************************)
 
+module External = struct
+  let external_channels = ref None
+
+  let get_external_channels resolver =
+    match !external_channels with
+      | Some channels -> channels
+      | None ->
+        let program = Path.to_string resolver in
+
+        let (child_r, parent_w) = Unix.pipe () in
+        let (parent_r, child_w) = Unix.pipe () in
+
+        let channels = (
+          (Unix.out_channel_of_descr parent_w),
+          (Unix.in_channel_of_descr parent_r)
+        ) in
+
+        ignore (Unix.create_process program [| program |] child_r child_w Unix.stderr);
+
+        external_channels := Some channels;
+        channels
+
+  let resolve_import opts f r =
+    match Options.module_resolver opts with
+      | None -> None
+      | Some resolver ->
+        let issuer = File_key.to_string f in
+        let payload = Printf.sprintf "[\"%s\", \"%s\"]\n" r issuer in
+
+        let (out_channel, in_channel) = (get_external_channels resolver) in
+
+        output_string out_channel payload;
+        Pervasives.flush out_channel;
+
+        Some (input_line in_channel)
+end
+
+(*******************************)
+
 module Node = struct
   let exported_module _ file _ =
     eponymous_module file
@@ -542,6 +581,7 @@ module Haste: MODULE_SYSTEM = struct
   let resolve_import ~options node_modules_containers f loc ?resolution_acc r =
     let file = File_key.to_string f in
     lazy_seq [
+      lazy (External.resolve_import options f r);
       lazy (Node.resolve_import ~options node_modules_containers f loc ?resolution_acc r);
       lazy (match expanded_name r with
         | Some r ->