[flow] Slight haste_namespace config tweak and add tests

Summary:
Previously, I reversed the list here because I think the lines in flowconfig are processed in order but they are prepended to the list in reverse order. However, that's my misunderstanding and flowconfig processing will reverse the lines first. This diff removes the reverse here to be consitent with other flowconfig options.

In addition, I also added the compatibility mode that allow common code to import 1-namespace only code (choosing the first namespace).

I also added test to test the namespace resolution behavior and the precedence rule change.

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D66710892

fbshipit-source-id: 728f804ddb40032cce62401e8a93a8fb35948fcc

src/common/haste_namespaces.ml

@@ -37,7 +37,7 @@ let mk_options =
         IMap.empty
     in
     let namespaces_path_mapping =
-      Base.List.rev_map haste_namespaces_path_mapping ~f:(fun (path, ns) ->
+      Base.List.map haste_namespaces_path_mapping ~f:(fun (path, ns) ->
           (map_path path, list_to_bitset ~haste_namespaces ns)
       )
     in
@@ -69,6 +69,20 @@ let reachable_namespace_bitsets_from_namespace_bitset ~opts ns =
           None
     )
   in
+  let additional =
+    match additional with
+    | Some _ -> additional
+    | None ->
+      if IMap.exists (fun _ b -> Bitset.equal b ns) opts.overlapping_namespaces_mapping then
+        Base.List.find_mapi (Nel.to_list opts.namespaces) ~f:(fun i _ ->
+            if Bitset.mem i ns then
+              Some (Bitset.all_zero size |> Bitset.set i)
+            else
+              None
+        )
+      else
+        None
+  in
   match additional with
   | Some ns' -> [ns; ns']
   | None -> [ns]

tests/haste_namespaces/.flowconfig

@@ -0,0 +1,9 @@
+[options]
+all=true
+module.system=haste
+module.system.haste.experimental.namespaces=web
+module.system.haste.experimental.namespaces=native
+module.system.haste.experimental.namespace_path_mapping='<PROJECT_ROOT>/common/web' -> 'web'
+module.system.haste.experimental.namespace_path_mapping='<PROJECT_ROOT>/common/' -> 'web,native'
+module.system.haste.experimental.namespace_path_mapping='<PROJECT_ROOT>/web/' -> 'web'
+module.system.haste.experimental.namespace_path_mapping='<PROJECT_ROOT>/native/' -> 'native'

tests/haste_namespaces/common/Common.js

@@ -0,0 +1,5 @@
+import { native } from "NativeOnly"; // error: common code cannot import native-only code
+import { web } from "WebOnly"; // ok: common code can import web-only code, because web-only code is treated as implicit common interface. TODO: common interface validation is missing for now
+
+web as empty; // error: string ~> empty
+native as empty;

tests/haste_namespaces/common/CommonLib.js

@@ -0,0 +1 @@
+declare export const foo: string;

tests/haste_namespaces/haste_namespaces.exp

@@ -0,0 +1,69 @@
+Error -------------------------------------------------------------------------------------------- common/Common.js:1:24
+
+Cannot resolve module `NativeOnly`. [cannot-resolve-module]
+
+   1| import { native } from "NativeOnly"; // error: common code cannot import native-only code
+                             ^^^^^^^^^^^^
+
+
+Error --------------------------------------------------------------------------------------------- common/Common.js:4:1
+
+Cannot cast `web` to empty because string [1] is incompatible with empty [2]. [incompatible-cast]
+
+   common/Common.js:4:1
+   4| web as empty; // error: string ~> empty
+      ^^^
+
+References:
+   web/WebOnly.js:6:27
+   6| declare export const web: string;
+                                ^^^^^^ [1]
+   common/Common.js:4:8
+   4| web as empty; // error: string ~> empty
+             ^^^^^ [2]
+
+
+Error ----------------------------------------------------------------------------------------- native/NativeOnly.js:4:1
+
+Cannot cast `foo` to empty because string [1] is incompatible with empty [2]. [incompatible-cast]
+
+   native/NativeOnly.js:4:1
+   4| foo as empty; // error: string ~> empty
+      ^^^
+
+References:
+   common/CommonLib.js:1:27
+   1| declare export const foo: string;
+                                ^^^^^^ [1]
+   native/NativeOnly.js:4:8
+   4| foo as empty; // error: string ~> empty
+             ^^^^^ [2]
+
+
+Error ----------------------------------------------------------------------------------------- native/NativeOnly.js:8:8
+
+Cannot resolve module `WebInCommon`. [cannot-resolve-module]
+
+   8| import 'WebInCommon' // error: native code cannot import web code. This one tests the precedence rule in flowconfig
+             ^^^^^^^^^^^^^
+
+
+Error ----------------------------------------------------------------------------------------------- web/WebOnly.js:4:1
+
+Cannot cast `foo` to empty because string [1] is incompatible with empty [2]. [incompatible-cast]
+
+   web/WebOnly.js:4:1
+   4| foo as empty; // error: string ~> empty
+      ^^^
+
+References:
+   common/CommonLib.js:1:27
+   1| declare export const foo: string;
+                                ^^^^^^ [1]
+   web/WebOnly.js:4:8
+   4| foo as empty; // error: string ~> empty
+             ^^^^^ [2]
+
+
+
+Found 5 errors

tests/haste_namespaces/native/NativeOnly.js

@@ -0,0 +1,8 @@
+import { foo } from "CommonLib";
+
+foo as string;
+foo as empty; // error: string ~> empty
+
+declare export const native: string;
+
+import 'WebInCommon' // error: native code cannot import web code. This one tests the precedence rule in flowconfig

tests/haste_namespaces/web/WebOnly.js

@@ -0,0 +1,6 @@
+import { foo } from "CommonLib";
+
+foo as string;
+foo as empty; // error: string ~> empty
+
+declare export const web: string;