[flow][get-def] Better heuristics for def_loc of module ref of requir…

…ed ESM module

Summary:
As discussed in D67869373, the current reason-based heuristic for module-ref logic is quite broken. This diff starts to use a new heuristic.

For ESM modules with default exports, we will use the default export as the def_loc of the require. Otherwise, we will pick the first export location instead. This is the same heuristic we use for the error location of common interface files: https://github.com/facebook/flow/blob/70811720be890cd85eb5dbf95fca2dbf960973bd/src/typing/module_info_analyzer.ml#L357-L389

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision:
D67875259

------------------------------------------------------------------------
(from 18d2b3f9e08ff3d4182c0e9ec04754a62157ac93)

fbshipit-source-id: c07d84a494db0cd5514416c35d6de422658af57b

src/typing/flow_js_utils.ml

@@ -1558,26 +1558,56 @@ module CJSRequireTKit = struct
         let types_tmap = Context.generate_property_map cx type_props in
         NamespaceT { namespace_symbol = module_symbol; values_type; types_tmap }
       in
-      if standard_cjs_esm_interop then
-        ( lookup_builtin_typeapp
+      let t =
+        if standard_cjs_esm_interop then
+          lookup_builtin_typeapp
             cx
             reason
             "$Flow$EsmModuleMarkerWrapperInModuleRef"
-            [mk_exports_namespace ()],
-          def_loc_of_reason reason
-        )
-      else
-        (* Use default export if option is enabled and module is not lib *)
-        let automatic_require_default =
-          (legacy_interop || Context.automatic_require_default cx)
-          && not (is_lib_reason_def module_reason)
-        in
-        if automatic_require_default then
-          match NameUtils.Map.find_opt (OrdinaryName "default") value_exports_tmap with
-          | Some { preferred_def_locs = _; name_loc = _; type_ } -> (type_, def_loc_of_t type_)
-          | _ -> (mk_exports_namespace (), def_loc_of_reason reason)
+            [mk_exports_namespace ()]
         else
-          (mk_exports_namespace (), def_loc_of_reason reason)
+          (* Use default export if option is enabled and module is not lib *)
+          let automatic_require_default =
+            (legacy_interop || Context.automatic_require_default cx)
+            && not (is_lib_reason_def module_reason)
+          in
+          if automatic_require_default then
+            match NameUtils.Map.find_opt (OrdinaryName "default") value_exports_tmap with
+            | Some { preferred_def_locs = _; name_loc = _; type_ } -> type_
+            | _ -> mk_exports_namespace ()
+          else
+            mk_exports_namespace ()
+      in
+      let def_loc =
+        let def_loc_of_export { preferred_def_locs; name_loc; type_ } =
+          match preferred_def_locs with
+          | Some l -> Nel.hd l
+          | None ->
+            (match name_loc with
+            | Some l -> l
+            | None -> def_loc_of_t type_)
+        in
+        match NameUtils.Map.find_opt (OrdinaryName "default") value_exports_tmap with
+        | Some e -> def_loc_of_export e
+        | None ->
+          (match
+             NameUtils.Map.fold
+               (fun _ e acc ->
+                 match acc with
+                 | None -> Some (def_loc_of_export e)
+                 | Some acc ->
+                   let def_loc = def_loc_of_export e in
+                   if ALoc.compare acc def_loc < 0 then
+                     Some acc
+                   else
+                     Some def_loc)
+               value_exports_tmap
+               None
+           with
+          | Some l -> l
+          | None -> def_loc_of_reason module_reason)
+      in
+      (t, def_loc)
 end
 
 (* import * as X from 'SomeModule'; *)

tests/get_def2/ParentESM2.js

@@ -0,0 +1,3 @@
+// @flow
+
+export const foo = 2;

tests/get_def2/get_def2.exp

@@ -140,7 +140,11 @@ Parent.js:4:18,4:28
 
 module_ref.js:5:4
 Flags:
-module_ref.js:5:1,5:15
+ParentESM.js:4:8,4:14
+
+module_ref.js:7:4
+Flags:
+ParentESM2.js:3:14,3:16
 
 refinements.js:10:4
 Flags:

tests/get_def2/module_ref.js

@@ -4,3 +4,5 @@
 // ^
 'm#./ParentESM';
 // ^
+'m#./ParentESM2';
+// ^