Add @flowtyped scope resolution before actual Node resolution

src/services/inference/module/module_js.ml

@@ -405,9 +405,33 @@ module Node = struct
       ])
     )
 
+  let flow_typed_node_module import_str =
+    let scoped_module_regex = Str.regexp "^@\\([a-zA-Z0-9$_.-]+\\)/\\(.*\\)$" in
+    if Str.string_match scoped_module_regex import_str 0 then
+      let scope = Str.matched_group 1 import_str in
+      let name = Str.matched_group 2 import_str in
+      scope ^ "__" ^ name
+    else
+      import_str
+
   let rec node_module ~options ~reader node_modules_containers file loc resolution_acc dir r =
     let file_options = Options.file_options options in
     lazy_seq [
+      lazy (
+        let flow_typed_r = spf
+          "%s%s%s"
+          "@flowtyped"
+          Filename.dir_sep
+          (flow_typed_node_module r)
+        in
+        if String_utils.string_starts_with r "@flowtyped" then
+          None
+        else
+          node_module
+            ~options ~reader node_modules_containers
+            file loc resolution_acc dir flow_typed_r
+      );
+
       lazy (
         if SSet.mem dir node_modules_containers then
           lazy_seq (Files.node_resolver_dirnames file_options |> Core_list.map ~f:(fun dirname ->

tests/declaration_files_node_flowtyped/.flowconfig

@@ -0,0 +1,7 @@
+[ignore]
+
+[include]
+
+[libs]
+
+[options]

tests/declaration_files_node_flowtyped/declaration_files_node_flowtyped.exp

@@ -0,0 +1,70 @@
+Error ------------------------------------------------------------------------------------ test_prefers_flowtyped.js:5:2
+
+Cannot cast `A.fun()` to string because number [1] is incompatible with string [2].
+
+   test_prefers_flowtyped.js:5:2
+   5| (A.fun(): string); // Error number ~> string
+       ^^^^^^^
+
+References:
+   node_modules/@flowtyped/foo/index.js.flow:3:32
+   3| declare export function fun(): number;
+                                     ^^^^^^ [1]
+   test_prefers_flowtyped.js:5:11
+   5| (A.fun(): string); // Error number ~> string
+                ^^^^^^ [2]
+
+
+Error ---------------------------------------------------------------------------------------------- test_regular.js:5:2
+
+Cannot cast `A.fun()` to number because string [1] is incompatible with number [2].
+
+   test_regular.js:5:2
+   5| (A.fun(): number); // Error string ~> number
+       ^^^^^^^
+
+References:
+   node_modules/baz/index.js.flow:3:32
+   3| declare export function fun(): string;
+                                     ^^^^^^ [1]
+   test_regular.js:5:11
+   5| (A.fun(): number); // Error string ~> number
+                ^^^^^^ [2]
+
+
+Error ----------------------------------------------------------------------------------------------- test_scoped.js:5:2
+
+Cannot cast `A.fun()` to string because number [1] is incompatible with string [2].
+
+   test_scoped.js:5:2
+   5| (A.fun(): string); // Error number ~> string
+       ^^^^^^^
+
+References:
+   node_modules/@flowtyped/foo__bar/index.js.flow:3:32
+   3| declare export function fun(): number;
+                                     ^^^^^^ [1]
+   test_scoped.js:5:11
+   5| (A.fun(): string); // Error number ~> string
+                ^^^^^^ [2]
+
+
+Error -------------------------------------------------------------------------------------------- test_with_main.js:5:2
+
+Cannot cast `A.fun()` to string because number [1] is incompatible with string [2].
+
+   test_with_main.js:5:2
+   5| (A.fun(): string); // Error number ~> string
+       ^^^^^^^
+
+References:
+   node_modules/@flowtyped/bar/code.js.flow:3:32
+   3| declare export function fun(): number;
+                                     ^^^^^^ [1]
+   test_with_main.js:5:11
+   5| (A.fun(): string); // Error number ~> string
+                ^^^^^^ [2]
+
+
+
+Found 4 errors

tests/declaration_files_node_flowtyped/test_prefers_flowtyped.js

@@ -0,0 +1,5 @@
+//@flow
+
+// This will require ./node_modules/@flowtyped/foo/index.js.flow
+var A = require('foo');
+(A.fun(): string); // Error number ~> string

tests/declaration_files_node_flowtyped/test_regular.js

@@ -0,0 +1,5 @@
+//@flow
+
+// This will require ./node_modules/baz/index.js.flow
+var A = require('baz');
+(A.fun(): number); // Error string ~> number

tests/declaration_files_node_flowtyped/test_scoped.js

@@ -0,0 +1,5 @@
+//@flow
+
+// This will require ./node_modules/@flowtyped/foo__bar/index.js.flow
+var A = require('@foo/bar');
+(A.fun(): string); // Error number ~> string

tests/declaration_files_node_flowtyped/test_with_main.js

@@ -0,0 +1,5 @@
+//@flow
+
+// This will require ./node_modules/@flowtyped/bar/code.js.flow
+var A = require('bar');
+(A.fun(): string); // Error number ~> string