[flow] More permissive what's allowed in declare namespace and declar…

…e module

Summary:
Right now, Flow complains about `export type` and `export interface` in `declare module` and `declare namespace` for no good reason. It is mostly a leftover of the past when the parser only permits `declare` statements in these body. This diff removes the restriction from Flow.

Changelog: [feature] `export type Foo = ...` and `export interface Bar {...}` statements are now allowed in `declare module` and `declare namespace` bodies.

Reviewed By: panagosg7

Differential Revision: D54989486

fbshipit-source-id: 5d27b88df2f6cde02cb8754c65589bb5dbba2fbd

src/parser/flow_ast_utils.ml

@@ -215,56 +215,60 @@ let is_super_member_access = function
   | { Flow_ast.Expression.Member._object = (_, Flow_ast.Expression.Super _); _ } -> true
   | _ -> false
 
-let acceptable_statement_in_declaration_context ~in_declare_namespace = function
-  | Flow_ast.Statement.Block _ -> Error "block"
-  | Flow_ast.Statement.Break _ -> Error "break"
-  | Flow_ast.Statement.ClassDeclaration _ -> Error "class declaration"
-  | Flow_ast.Statement.ComponentDeclaration _ -> Error "component declaration"
-  | Flow_ast.Statement.Continue _ -> Error "continue"
-  | Flow_ast.Statement.Debugger _ -> Error "debugger"
-  | Flow_ast.Statement.DoWhile _ -> Error "do while"
-  | Flow_ast.Statement.ExportDefaultDeclaration _ -> Error "export"
-  | Flow_ast.Statement.ExportNamedDeclaration _ -> Error "export"
-  | Flow_ast.Statement.Expression _ -> Error "expression"
-  | Flow_ast.Statement.For _ -> Error "for"
-  | Flow_ast.Statement.ForIn _ -> Error "for in"
-  | Flow_ast.Statement.ForOf _ -> Error "for of"
-  | Flow_ast.Statement.FunctionDeclaration _ -> Error "function declaration"
-  | Flow_ast.Statement.If _ -> Error "if"
-  | Flow_ast.Statement.Labeled _ -> Error "labeled"
-  | Flow_ast.Statement.Return _ -> Error "return"
-  | Flow_ast.Statement.Switch _ -> Error "switch"
-  | Flow_ast.Statement.Throw _ -> Error "throw"
-  | Flow_ast.Statement.Try _ -> Error "try"
-  | Flow_ast.Statement.VariableDeclaration _ -> Error "variable declaration"
-  | Flow_ast.Statement.While _ -> Error "while"
-  | Flow_ast.Statement.With _ -> Error "with"
-  | Flow_ast.Statement.ImportDeclaration _ ->
+let acceptable_statement_in_declaration_context ~in_declare_namespace =
+  let open Flow_ast.Statement in
+  function
+  | Block _ -> Error "block"
+  | Break _ -> Error "break"
+  | ClassDeclaration _ -> Error "class declaration"
+  | ComponentDeclaration _ -> Error "component declaration"
+  | Continue _ -> Error "continue"
+  | Debugger _ -> Error "debugger"
+  | DoWhile _ -> Error "do while"
+  | ExportDefaultDeclaration _ -> Error "export default"
+  | ExportNamedDeclaration { ExportNamedDeclaration.export_kind = ExportValue; _ } ->
+    Error "value export"
+  | Expression _ -> Error "expression"
+  | For _ -> Error "for"
+  | ForIn _ -> Error "for in"
+  | ForOf _ -> Error "for of"
+  | FunctionDeclaration _ -> Error "function declaration"
+  | If _ -> Error "if"
+  | Labeled _ -> Error "labeled"
+  | Return _ -> Error "return"
+  | Switch _ -> Error "switch"
+  | Throw _ -> Error "throw"
+  | Try _ -> Error "try"
+  | VariableDeclaration _ -> Error "variable declaration"
+  | While _ -> Error "while"
+  | With _ -> Error "with"
+  | ImportDeclaration _ ->
     if in_declare_namespace then
       Error "import declaration"
     else
       Ok ()
-  | Flow_ast.Statement.DeclareModuleExports _ ->
+  | DeclareModuleExports _ ->
     if in_declare_namespace then
       Error "declare module.exports"
     else
       Ok ()
-  | Flow_ast.Statement.DeclareClass _
-  | Flow_ast.Statement.DeclareComponent _
-  | Flow_ast.Statement.DeclareEnum _
-  | Flow_ast.Statement.DeclareExportDeclaration _
-  | Flow_ast.Statement.DeclareFunction _
-  | Flow_ast.Statement.DeclareInterface _
-  | Flow_ast.Statement.DeclareModule _
-  | Flow_ast.Statement.DeclareNamespace _
-  | Flow_ast.Statement.DeclareOpaqueType _
-  | Flow_ast.Statement.DeclareTypeAlias _
-  | Flow_ast.Statement.DeclareVariable _
-  | Flow_ast.Statement.Empty _
-  | Flow_ast.Statement.EnumDeclaration _
-  | Flow_ast.Statement.InterfaceDeclaration _
-  | Flow_ast.Statement.OpaqueType _
-  | Flow_ast.Statement.TypeAlias _ ->
+  | DeclareClass _
+  | DeclareComponent _
+  | DeclareEnum _
+  | DeclareExportDeclaration _
+  | DeclareFunction _
+  | DeclareInterface _
+  | DeclareModule _
+  | DeclareNamespace _
+  | DeclareOpaqueType _
+  | DeclareTypeAlias _
+  | DeclareVariable _
+  | Empty _
+  | EnumDeclaration _
+  | ExportNamedDeclaration { ExportNamedDeclaration.export_kind = ExportType; _ }
+  | InterfaceDeclaration _
+  | OpaqueType _
+  | TypeAlias _ ->
     Ok ()
 
 let rec is_type_only_declaration_statement (_, stmt') =
@@ -284,6 +288,7 @@ let rec is_type_only_declaration_statement (_, stmt') =
       true
     | DeclareNamespace { DeclareNamespace.body = (_, { Block.body; _ }); _ } ->
       List.for_all is_type_only_declaration_statement body
+    | ExportNamedDeclaration { ExportNamedDeclaration.export_kind; _ } -> export_kind = ExportType
     | Block _
     | Break _
     | ClassDeclaration _
@@ -293,7 +298,6 @@ let rec is_type_only_declaration_statement (_, stmt') =
     | DoWhile _
     | EnumDeclaration _
     | ExportDefaultDeclaration _
-    | ExportNamedDeclaration _
     | Expression _
     | For _
     | ForIn _

src/parser_utils/type_sig/__tests__/type_sig_tests.ml

@@ -5566,19 +5566,25 @@ let%expect_test "builtin_cjs_module_auto_export_type" =
   (* All types in cjs modules are auto exported. *)
   print_builtins [{|
     declare module foo {
-      declare type T = number;
+      declare type T1 = number;
+      export type T2 = string;
       declare module.exports: string;
     }
   |}];
   [%expect {|
     Local defs:
-    0. TypeAlias {id_loc = [2:15-16]; name = "T"; tparams = Mono; body = (Annot (Number [2:19-25]))}
+    0. TypeAlias {id_loc = [2:15-17];
+         name = "T1"; tparams = Mono;
+         body = (Annot (Number [2:20-26]))}
+    1. TypeAlias {id_loc = [3:14-16];
+         name = "T2"; tparams = Mono;
+         body = (Annot (String [3:19-25]))}
 
     Builtin module foo:
-    [1:15-18] CJSModule {type_exports = [|(ExportTypeBinding 0)|];
-                exports = (Some (Annot (String [3:26-32])));
+    [1:15-18] CJSModule {type_exports = [|(ExportTypeBinding 0); (ExportTypeBinding 1)|];
+                exports = (Some (Annot (String [4:26-32])));
                 info =
-                CJSModuleInfo {type_export_keys = [|"T"|];
+                CJSModuleInfo {type_export_keys = [|"T1"; "T2"|];
                   type_stars = []; strict = true;
                   platform_availability_set = None}} |}]
 
@@ -5667,6 +5673,7 @@ let%expect_test "builtin_cjs_module_with_implicit_exports" =
       declare enum A { B }
       declare type T = number;
       declare export type U = string;
+      export const ignored = 3; // unsupported;
     }
   |}];
   [%expect {|
@@ -5881,11 +5888,14 @@ let%expect_test "builtin_declare_namespace" =
       declare function f(): string;
       declare function f(): number;
       declare type Baz = string;
+      export type Boz = string;
       enum B {
         C,
         D,
       }
       if (true) {} // unsupported
+      export const foo = ''; // unsupported
+      export default foo; // unsupported
       declare module.exports: {foo: string}; // unsupported
       import React from 'react'; // unsupported
     }
@@ -5912,19 +5922,24 @@ let%expect_test "builtin_declare_namespace" =
     4. TypeAlias {id_loc = [7:15-18];
          name = "Baz"; tparams = Mono;
          body = (Annot (String [7:21-27]))}
-    5. EnumBinding {id_loc = [8:7-8];
+    5. TypeAlias {id_loc = [8:14-17];
+         name = "Boz"; tparams = Mono;
+         body = (Annot (String [8:20-26]))}
+    6. EnumBinding {id_loc = [9:7-8];
          name = "B"; rep = StringRep {truthy = true};
-         members = { "C" -> [9:4-5]; "D" -> [10:4-5] };
+         members = { "C" -> [10:4-5]; "D" -> [11:4-5] };
          has_unknown_members = false}
-    6. NamespaceBinding {id_loc = [1:18-20];
+    7. NamespaceBinding {id_loc = [1:18-20];
          name = "ns";
          values =
-         { "B" -> ([8:7-8], (Ref LocalRef {ref_loc = [8:7-8]; index = 5}));
+         { "B" -> ([9:7-8], (Ref LocalRef {ref_loc = [9:7-8]; index = 6}));
            "bar1" -> ([2:23-27], (Ref LocalRef {ref_loc = [2:23-27]; index = 0}));
            "bar2" -> ([3:16-20], (Ref LocalRef {ref_loc = [3:16-20]; index = 1}));
            "bar3" -> ([4:14-18], (Ref LocalRef {ref_loc = [4:14-18]; index = 2}));
            "f" -> ([5:19-20], (Ref LocalRef {ref_loc = [5:19-20]; index = 3})) };
-         types = { "Baz" -> ([7:15-18], (Ref LocalRef {ref_loc = [7:15-18]; index = 4})) }}
+         types =
+         { "Baz" -> ([7:15-18], (Ref LocalRef {ref_loc = [7:15-18]; index = 4}));
+           "Boz" -> ([8:14-17], (Ref LocalRef {ref_loc = [8:14-17]; index = 5})) }}
 
     Builtin global value ns |}]
 

src/typing/errors/error_message.ml

@@ -3182,22 +3182,22 @@ let friendly_message_of_msg loc_of_aloc msg =
       | ContextDependentUnsupportedStatement (UnsupportedStatementInLibdef kind) ->
         [
           text "Cannot use ";
-          code kind;
+          text kind;
           text " statements in a library file. ";
           text "The statement will be ignored.";
         ]
       | ContextDependentUnsupportedStatement (UnsupportedStatementInDeclareModule kind) ->
         [
           text "Cannot use ";
-          code kind;
+          text kind;
           text " statements with in ";
           code "declare module";
           text ". The statement will be ignored.";
         ]
       | ContextDependentUnsupportedStatement (UnsupportedStatementInDeclareNamespace kind) ->
         [
           text "Cannot use ";
-          code kind;
+          text kind;
           text " statements with in ";
           code "declare namespace";
           text ". The statement will be ignored.";

src/typing/type_inference_js.ml

@@ -433,7 +433,7 @@ class lib_def_loc_mapper_and_validator cx =
       | OpaqueType _ ->
         None
       | ExportNamedDeclaration { ExportNamedDeclaration.export_kind = ExportValue; _ } ->
-        Some (error "export")
+        Some (error "value export")
       | ImportDeclaration _ ->
         if in_toplevel_scope then
           Some