[FEATURE] Add module_alias resolution capabilities

src/commands/commandUtils.ml

@@ -564,6 +564,7 @@ let file_options =
       module_file_exts = FlowConfig.module_file_exts flowconfig;
       module_resource_exts = FlowConfig.module_resource_exts flowconfig;
       node_resolver_dirnames = FlowConfig.node_resolver_dirnames flowconfig;
+      node_resolver_aliases = FlowConfig.node_resolver_aliases flowconfig
     }
 
 let ignore_flag prev = CommandSpec.ArgSpec.(

src/commands/config/flowConfig.ml

@@ -69,6 +69,7 @@ module Opts = struct
     munge_underscores: bool;
     no_flowlib: bool;
     node_resolver_dirnames: string list;
+    node_resolver_aliases: string list;
     root_name: string option;
     saved_state_fetcher: Options.saved_state_fetcher;
     shm_dep_table_pow: int;
@@ -155,6 +156,7 @@ module Opts = struct
     munge_underscores = false;
     no_flowlib = false;
     node_resolver_dirnames = ["node_modules"];
+    node_resolver_aliases = [];
     root_name = None;
     saved_state_fetcher = Options.Dummy_fetcher;
     shm_dep_table_pow = 17;
@@ -486,6 +488,15 @@ module Opts = struct
           let node_resolver_dirnames = v :: opts.node_resolver_dirnames in
           Ok {opts with node_resolver_dirnames;}
         );
+
+    "module.system.node.resolve_alias",
+      string
+        ~init: (fun opts -> { opts with node_resolver_aliases = [] })
+        ~multiple: true
+        (fun opts v ->
+          let node_resolver_aliases = v :: opts.node_resolver_aliases in
+          Ok {opts with node_resolver_aliases;}
+        );
 
     "module.use_strict",
       boolean (fun opts v -> Ok { opts with modules_are_use_strict = v });
@@ -991,6 +1002,7 @@ let modules_are_use_strict c = c.options.Opts.modules_are_use_strict
 let munge_underscores c = c.options.Opts.munge_underscores
 let no_flowlib c = c.options.Opts.no_flowlib
 let node_resolver_dirnames c = c.options.Opts.node_resolver_dirnames
+let node_resolver_aliases c = c.options.Opts.node_resolver_aliases
 let root_name c = c.options.Opts.root_name
 let saved_state_fetcher c = c.options.Opts.saved_state_fetcher
 let shm_dep_table_pow c = c.options.Opts.shm_dep_table_pow

src/commands/config/flowConfig.mli

@@ -75,6 +75,7 @@ val modules_are_use_strict: config -> bool
 val munge_underscores: config -> bool
 val no_flowlib: config -> bool
 val node_resolver_dirnames: config -> string list
+val node_resolver_aliases: config -> string list
 val required_version: config -> string option
 val root_name: config -> string option
 val saved_state_fetcher: config -> Options.saved_state_fetcher

src/common/files.ml

@@ -17,6 +17,7 @@ type options = {
   module_file_exts: SSet.t;
   module_resource_exts: SSet.t;
   node_resolver_dirnames: string list;
+  node_resolver_aliases: string list;
 }
 
 let default_lib_dir options = options.default_lib_dir
@@ -28,6 +29,7 @@ let lib_paths options = options.lib_paths
 let module_file_exts options = options.module_file_exts
 let module_resource_exts options = options.module_resource_exts
 let node_resolver_dirnames options = options.node_resolver_dirnames
+let node_resolver_aliases options = options.node_resolver_aliases
 
 let node_modules_containers = ref SSet.empty
 
@@ -104,6 +106,9 @@ let is_valid_path =
 let is_node_module options path =
   List.mem (Filename.basename path) options.node_resolver_dirnames
 
+let is_module_alias options path =
+  List.mem (Filename.basename path) options.node_resolver_aliases
+
 let is_flow_file ~options =
   let is_valid_path = is_valid_path ~options in
   fun path -> is_valid_path path && not (is_directory path)
@@ -177,7 +182,7 @@ let max_files = 1000
 
     If kind_of_path fails, then we only emit a warning if error_filter passes *)
 let make_next_files_and_symlinks
-    ~node_module_filter ~path_filter ~realpath_filter ~error_filter paths =
+    ~node_module_filter ~module_alias_filter ~path_filter ~realpath_filter ~error_filter paths =
   let prefix_checkers = Core_list.map ~f:is_prefix paths in
   let rec process sz (acc, symlinks) files dir stack =
     if sz >= max_files then
@@ -193,7 +198,7 @@ let make_next_files_and_symlinks
           then process (sz+1) (real :: acc, symlinks) files dir stack
           else process sz (acc, symlinks) files dir stack
         | Dir (path, is_symlink) ->
-          if node_module_filter file
+          if node_module_filter file || module_alias_filter file
           then node_modules_containers := SSet.add (Filename.dirname file) !node_modules_containers;
           let dirfiles = Array.to_list @@ try_readdir path in
           let symlinks =
@@ -229,13 +234,14 @@ let make_next_files_and_symlinks
    of `paths`. *)
 let make_next_files_following_symlinks
   ~node_module_filter
+  ~module_alias_filter
   ~path_filter
   ~realpath_filter
   ~error_filter
   paths =
   let paths = Core_list.map ~f:Path.to_string paths in
   let cb = ref (make_next_files_and_symlinks
-    ~node_module_filter ~path_filter ~realpath_filter ~error_filter paths
+    ~node_module_filter ~module_alias_filter ~path_filter ~realpath_filter ~error_filter paths
   ) in
   let symlinks = ref SSet.empty in
   let seen_symlinks = ref SSet.empty in
@@ -254,7 +260,7 @@ let make_next_files_following_symlinks
       symlinks := SSet.empty;
       (* since we're following a symlink, use realpath_filter for both *)
       cb := make_next_files_and_symlinks
-        ~node_module_filter ~path_filter:realpath_filter ~realpath_filter ~error_filter paths;
+        ~node_module_filter ~module_alias_filter ~path_filter:realpath_filter ~realpath_filter ~error_filter paths;
       rec_cb ()
     end
   in
@@ -273,6 +279,7 @@ let get_all =
 
 let init ?(flowlibs_only=false) (options: options) =
   let node_module_filter = is_node_module options in
+  let module_alias_filter = is_module_alias options in
   let libs = if flowlibs_only then [] else options.lib_paths in
   let libs, filter = match options.default_lib_dir with
     | None -> libs, is_valid_path ~options
@@ -291,6 +298,7 @@ let init ?(flowlibs_only=false) (options: options) =
         let filter' path = path = lib_str || filter path in
         make_next_files_following_symlinks
           ~node_module_filter
+          ~module_alias_filter
           ~path_filter:filter'
           ~realpath_filter:filter'
           ~error_filter:(fun _ -> true)
@@ -364,6 +372,7 @@ let watched_paths options =
  *)
 let make_next_files ~root ~all ~subdir ~options ~libs =
   let node_module_filter = is_node_module options in
+  let module_alias_filter = is_module_alias options in
   let filter = if all then fun _ -> true else wanted ~options libs in
 
   (* The directories from which we start our search *)
@@ -399,7 +408,7 @@ let make_next_files ~root ~all ~subdir ~options ~libs =
       )
   in
   make_next_files_following_symlinks
-    ~node_module_filter ~path_filter ~realpath_filter ~error_filter:filter starting_points
+    ~node_module_filter ~module_alias_filter ~path_filter ~realpath_filter ~error_filter:filter starting_points
 
 let is_windows_root root =
   Sys.win32 &&
@@ -527,6 +536,14 @@ let is_within_node_modules ~root ~options path =
   let node_resolver_dirnames = node_resolver_dirnames options |> SSet.of_list in
   not (SSet.inter directories node_resolver_dirnames |> SSet.is_empty)
 
+(* Given a path, we want to know if it's a resolve alias. *)
+let is_within_alias_directory ~root ~options path =
+  (* We use paths that are relative to the root, so that we ignore ancestor directories *)
+  let path = relative_path (Path.to_string root) path in
+  let directories = Str.split dir_sep path |> SSet.of_list in
+  let node_resolver_aliases = node_resolver_aliases options |> SSet.of_list in
+  not (SSet.inter directories node_resolver_aliases |> SSet.is_empty)
+
 (* realpath doesn't work for non-existent paths. So let's find the longest existent prefix, run
  * realpath on that, and then append the rest to it
  *)

src/common/files.mli

@@ -17,6 +17,7 @@ type options = {
   module_file_exts: SSet.t;
   module_resource_exts: SSet.t;
   node_resolver_dirnames: string list;
+  node_resolver_aliases: string list;
 }
 
 val default_lib_dir: options -> Path.t option
@@ -28,6 +29,7 @@ val lib_paths: options -> Path.t list
 val module_file_exts: options -> SSet.t
 val module_resource_exts: options -> SSet.t
 val node_resolver_dirnames: options -> string list
+val node_resolver_aliases: options -> string list
 
 val node_modules_containers: SSet.t ref
 
@@ -106,6 +108,7 @@ val filename_from_string: options: options -> string -> File_key.t
 val mkdirp: string -> Unix.file_perm -> unit
 
 val is_within_node_modules: root:Path.t -> options: options -> string -> bool
+val is_within_alias_directory: root:Path.t -> options: options -> string -> bool
 
 val imaginary_realpath: string -> string
 val canonicalize_filenames:

src/services/inference/module/module_js.ml

@@ -407,12 +407,24 @@ module Node = struct
     lazy_seq [
       lazy (
         if SSet.mem dir node_modules_containers then
-          lazy_seq (Files.node_resolver_dirnames file_options |> Core_list.map ~f:(fun dirname ->
-            lazy (resolve_relative
-              ~options ~reader
-              loc ?resolution_acc dir (spf "%s%s%s" dirname Filename.dir_sep r)
-            )
-          ))
+          lazy_seq([
+            lazy (
+              lazy_seq (Files.node_resolver_aliases file_options |> Core_list.map ~f:(fun dirname ->
+                lazy (resolve_relative
+                  ~options ~reader
+                  loc ?resolution_acc dir (spf "%s%s%s" dirname Filename.dir_sep r)
+                )
+              ))
+            );
+            lazy (
+              lazy_seq (Files.node_resolver_dirnames file_options |> Core_list.map ~f:(fun dirname ->
+                lazy (resolve_relative
+                  ~options ~reader
+                  loc ?resolution_acc dir (spf "%s%s%s" dirname Filename.dir_sep r)
+                )
+              ))
+            );
+          ])
         else None
       );
 

tests/config_module_system_node_resolve_alias/.flowconfig

@@ -0,0 +1,7 @@
+[options]
+module.system.node.resolve_dirname=node_modules
+module.system.node.resolve_dirname=custom_node_modules
+module.system.node.resolve_alias=custom_resolve_dir
+; should also be able to specify as
+; <PROJECT_ROOT>/root_resolve_dir
+module.system.node.resolve_alias=./root_resolve_dir

tests/config_module_system_node_resolve_alias/config_module_system_node_resolve_alias.exp

@@ -0,0 +1,56 @@
+Error ------------------------------------------------------------------------------------------ subdir/sublevel.js:12:2
+
+Cannot cast `two` to string literal `custom_resolve_dir/testproj2` because string literal
+`subdir/custom_resolve_dir/testproj2` [1] is incompatible with string literal `custom_resolve_dir/testproj2` [2].
+
+   subdir/sublevel.js:12:2
+   12| (two: "custom_resolve_dir/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+        ^^^
+
+References:
+   subdir/custom_resolve_dir/testproj2/index.js:3:18
+    3| export var name: "subdir/custom_resolve_dir/testproj2" = "subdir/custom_resolve_dir/testproj2";
+                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [1]
+   subdir/sublevel.js:12:7
+   12| (two: "custom_resolve_dir/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [2]
+
+
+Error ------------------------------------------------------------------------------------------ subdir/sublevel.js:13:2
+
+Cannot cast `two` to string literal `node_modules/testproj2` because string literal
+`subdir/custom_resolve_dir/testproj2` [1] is incompatible with string literal `node_modules/testproj2` [2].
+
+   subdir/sublevel.js:13:2
+   13| (two: "node_modules/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+        ^^^
+
+References:
+   subdir/custom_resolve_dir/testproj2/index.js:3:18
+    3| export var name: "subdir/custom_resolve_dir/testproj2" = "subdir/custom_resolve_dir/testproj2";
+                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [1]
+   subdir/sublevel.js:13:7
+   13| (two: "node_modules/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+             ^^^^^^^^^^^^^^^^^^^^^^^^ [2]
+
+
+Error -------------------------------------------------------------------------------------------------- toplevel.js:7:2
+
+Cannot cast `one` to string literal `node_modules/testproj` because string literal `custom_resolve_dir/testproj` [1] is
+incompatible with string literal `node_modules/testproj` [2].
+
+   toplevel.js:7:2
+   7| (one: "node_modules/testproj"); // Error: Resolve from resolve_alias first!
+       ^^^
+
+References:
+   custom_resolve_dir/testproj/index.js:3:18
+   3| export var name: "custom_resolve_dir/testproj" = "custom_resolve_dir/testproj";
+                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [1]
+   toplevel.js:7:7
+   7| (one: "node_modules/testproj"); // Error: Resolve from resolve_alias first!
+            ^^^^^^^^^^^^^^^^^^^^^^^ [2]
+
+
+
+Found 3 errors

tests/config_module_system_node_resolve_alias/custom_resolve_dir/testproj/index.js

@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "custom_resolve_dir/testproj" = "custom_resolve_dir/testproj";

tests/config_module_system_node_resolve_alias/custom_resolve_dir/testproj2/index.js

@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "custom_resolve_dir/testproj2" = "custom_resolve_dir/testproj2";

tests/config_module_system_node_resolve_alias/jsconfig.json

@@ -0,0 +1,8 @@
+{
+  "compilerOptions": {
+    "baseUrl": ".",
+    "paths": {
+      "*": ["./src/*"]
+    }
+  }
+}

tests/config_module_system_node_resolve_alias/root_resolve_dir/testproj6/index.js

@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "root_resolve_dir/testproj6" = "root_resolve_dir/testproj6";

tests/config_module_system_node_resolve_alias/subdir/custom_resolve_dir/testproj2/index.js

@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "subdir/custom_resolve_dir/testproj2" = "subdir/custom_resolve_dir/testproj2";

tests/config_module_system_node_resolve_alias/subdir/custom_resolve_dir/testproj5/index.js

@@ -0,0 +1,4 @@
+// @flow
+
+export var name: "subdir/custom_resolve_dir/testproj5" =
+  "subdir/custom_resolve_dir/testproj5";

tests/config_module_system_node_resolve_alias/subdir/root_resolve_dir/testproj6/index.js

@@ -0,0 +1,4 @@
+// @flow
+
+export var name: "subdir/root_resolve_dir/testproj6" =
+  "subdir/root_resolve_dir/testproj6";

tests/config_module_system_node_resolve_alias/subdir/sublevel.js

@@ -0,0 +1,39 @@
+// @flow
+import { name as one } from "testproj";
+import { name as two } from "testproj2";
+import { name as three } from "testproj2/subfile";
+
+import { name as four } from "testproj3";
+import { name as five } from "testproj4";
+
+import { name as six } from "testproj5";
+
+import { name as seven } from "testproj6";
+
+(one: "custom_resolve_dir/testproj");
+
+(two: "subdir/custom_resolve_dir/testproj2");
+(two: "custom_resolve_dir/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+(two: "node_modules/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+
+// if we fail to resolve in custom_resolve_dir
+// then we should still resolve node_modules if
+// possible.
+//
+// this tends to bring up the possibility of
+// confusing bugs but it is consistent with
+// the behavior of the webpack/babel features
+// they are based upon.
+//
+// personally can see a flow lint warning
+// as an option here if a conflict of folders
+// is detected between aliases and/or node_modules
+(three: "node_modules/testproj2/subfile");
+
+// should still resolve node_modules
+(four: "node_modules/testproj3");
+
+// should still resolve custom_node_modules
+(five: "custom_node_modules/testproj4");
+
+(seven: "root_resolve_dir/testproj6/");