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samwgoldmanFacebook Github Bot
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Expose EmptyT as type annotation empty
Summary: A few people on GitHub have come up with hacky ways to mimic this type, like `string & number`, but they aren't quite the same. I think the utility here is pretty marginal, but I'm confident that exposing this type is at least neutral and should not have any negative effects. Until reachability lands, `empty` can verify that Flow is convinced of exhaustiveness. ``` function exhaust(x: number | string) { if (typeof x === "number") { // do stuff } else if (typeof x === "string") { // do different stuff } else { // only true if we handled all cases (x: empty); } } ``` I considered that `empty` might confound/confuse poly instantiation, for example by satisfying a generic type in a way that breaks parametricity. Well, kind of, but you need to use `declare var` ``` function f<T>(): T { declare var x: empty; return x; } ``` and of course the same trick would work with `declare var x: T`, so I think we're OK. Without `declare var`, we can devise a function that passes local inference, but is uncallable. ``` function f<T>(x: empty): T { return x; } f(); // nothing to pass... ``` Reviewed By: avikchaudhuri Differential Revision: D3979445 fbshipit-source-id: 911d70dbf7159968d70e7c56d55b9aba4df41e71
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7 files changed

+30
-20
lines changed

7 files changed

+30
-20
lines changed

Diff for: ‎src/common/reason.ml

+1-1
Original file line numberDiff line numberDiff line change
@@ -346,7 +346,7 @@ let rec string_of_desc = function
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| RString -> "string"
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| RBoolean -> "boolean"
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| RMixed -> "mixed"
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| REmpty -> ""
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| REmpty -> "empty"
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| RAny -> "any"
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| RVoid -> "undefined"
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| RNull -> "null"

Diff for: ‎src/parser/estree_translator.ml

+3
Original file line numberDiff line numberDiff line change
@@ -919,6 +919,7 @@ end with type t = Impl.t) = struct
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match t with
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| Any -> any_type loc
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| Mixed -> mixed_type loc
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| Empty -> empty_type loc
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| Void -> void_type loc
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| Null -> null_type loc
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| Number -> number_type loc
@@ -943,6 +944,8 @@ end with type t = Impl.t) = struct
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and mixed_type loc = node "MixedTypeAnnotation" loc [||]
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and empty_type loc = node "EmptyTypeAnnotation" loc [||]
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and void_type loc = node "VoidTypeAnnotation" loc [||]
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and null_type loc = node "NullTypeAnnotation" loc [||]

Diff for: ‎src/parser/lexer_flow.mll

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Original file line numberDiff line numberDiff line change
@@ -136,6 +136,7 @@ module Token = struct
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(* Type primitives *)
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| T_ANY_TYPE
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| T_MIXED_TYPE
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| T_EMPTY_TYPE
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| T_BOOLEAN_TYPE
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| T_NUMBER_TYPE
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| T_NUMBER_SINGLETON_TYPE of number_type * float
@@ -277,6 +278,7 @@ module Token = struct
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(* Type primitives *)
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| T_ANY_TYPE -> "T_ANY_TYPE"
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| T_MIXED_TYPE -> "T_MIXED_TYPE"
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| T_EMPTY_TYPE -> "T_EMPTY_TYPE"
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| T_BOOLEAN_TYPE -> "T_BOOLEAN_TYPE"
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| T_NUMBER_TYPE -> "T_NUMBER_TYPE"
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| T_NUMBER_SINGLETON_TYPE _ -> "T_NUMBER_SINGLETON_TYPE"
@@ -728,6 +730,7 @@ end
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"typeof", T_TYPEOF;
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"any", T_ANY_TYPE;
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"mixed", T_MIXED_TYPE;
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"empty", T_EMPTY_TYPE;
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"bool", T_BOOLEAN_TYPE;
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"boolean", T_BOOLEAN_TYPE;
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"true", T_TRUE;

Diff for: ‎src/parser/parser_flow.ml

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Original file line numberDiff line numberDiff line change
@@ -260,6 +260,7 @@ end = struct
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and primitive = function
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| T_ANY_TYPE -> Some Type.Any
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| T_MIXED_TYPE -> Some Type.Mixed
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| T_EMPTY_TYPE -> Some Type.Empty
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| T_BOOLEAN_TYPE -> Some Type.Boolean
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| T_NUMBER_TYPE -> Some Type.Number
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| T_STRING_TYPE -> Some Type.String

Diff for: ‎src/parser/spider_monkey_ast.ml

+1
Original file line numberDiff line numberDiff line change
@@ -152,6 +152,7 @@ and Type : sig
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and t' =
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| Any
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| Mixed
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| Empty
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| Void
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| Null
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| Number

Diff for: ‎src/typing/type_annotation.ml

+2
Original file line numberDiff line numberDiff line change
@@ -55,6 +55,8 @@ let rec convert cx tparams_map = Ast.Type.(function
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| loc, Mixed -> MixedT.at loc
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| loc, Empty -> EmptyT.at loc
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| loc, Void -> VoidT.at loc
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| loc, Null -> NullT.at loc

Diff for: ‎tests/dump-types/dump-types.exp

+19-19
Original file line numberDiff line numberDiff line change
@@ -225,7 +225,7 @@
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"end":18
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},
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{
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"type":"(x: ) => ",
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"type":"(x: empty) => empty",
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"reasons":[],
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"loc":{
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"source":"test.js",
@@ -240,7 +240,7 @@
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"end":20
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},
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{
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"type":"",
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"type":"empty",
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"reasons":[],
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"loc":{
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"source":"test.js",
@@ -255,7 +255,7 @@
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"end":22
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},
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{
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"type":"",
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"type":"empty",
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"reasons":[],
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"loc":{
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"source":"test.js",
@@ -555,7 +555,7 @@
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"end":50
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},
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{
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"desc":"",
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"desc":"empty",
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"loc":{
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"source":"test.js",
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"type":"SourceFile",
@@ -569,7 +569,7 @@
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"end":50
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},
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{
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"desc":"",
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"desc":"empty",
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"loc":{
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"source":"test.js",
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"type":"SourceFile",
@@ -583,7 +583,7 @@
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"end":50
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},
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{
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"desc":"",
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"desc":"empty",
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"loc":{
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"source":"test.js",
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"type":"SourceFile",
@@ -597,7 +597,7 @@
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"end":50
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},
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{
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"desc":"",
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"desc":"empty",
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"loc":{
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"source":"test.js",
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"type":"SourceFile",
@@ -754,7 +754,7 @@
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"end":34
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},
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{
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"desc":"",
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"desc":"empty",
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"loc":{
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"source":"test.js",
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"type":"SourceFile",
@@ -1838,8 +1838,8 @@
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"end":18
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},
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{
1841-
"raw_type":"{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"function\"\n },\n \"kind\":\"FunT\",\n \"static\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"statics of function\"\n },\n \"kind\":\"AnyFunT\"\n },\n \"prototype\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"empty prototype object\"\n },\n \"kind\":\"MixedT\"\n },\n \"funType\":{\n \"thisType\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"global object\"\n },\n \"kind\":\"MixedT\"\n },\n \"paramTypes\":[\n {\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"\"\n },\n \"kind\":\"EmptyT\"\n }\n ],\n \"paramNames\":[\"x\"],\n \"returnType\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"\"\n },\n \"kind\":\"EmptyT\"\n },\n \"isPredicate\":false,\n \"closureIndex\":0,\n \"changeset\":{\"vars\":[],\"refis\":[]}\n }\n}",
1842-
"type":"(x: ) => ",
1841+
"raw_type":"{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"function\"\n },\n \"kind\":\"FunT\",\n \"static\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"statics of function\"\n },\n \"kind\":\"AnyFunT\"\n },\n \"prototype\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"empty prototype object\"\n },\n \"kind\":\"MixedT\"\n },\n \"funType\":{\n \"thisType\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"global object\"\n },\n \"kind\":\"MixedT\"\n },\n \"paramTypes\":[\n {\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"empty\"\n },\n \"kind\":\"EmptyT\"\n }\n ],\n \"paramNames\":[\"x\"],\n \"returnType\":{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"empty\"\n },\n \"kind\":\"EmptyT\"\n },\n \"isPredicate\":false,\n \"closureIndex\":0,\n \"changeset\":{\"vars\":[],\"refis\":[]}\n }\n}",
1842+
"type":"(x: empty) => empty",
18431843
"reasons":[],
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"loc":{
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"source":"test.js",
@@ -1854,8 +1854,8 @@
18541854
"end":20
18551855
},
18561856
{
1857-
"raw_type":"{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"\"\n },\n \"kind\":\"EmptyT\"\n}",
1858-
"type":"",
1857+
"raw_type":"{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"empty\"\n },\n \"kind\":\"EmptyT\"\n}",
1858+
"type":"empty",
18591859
"reasons":[],
18601860
"loc":{
18611861
"source":"test.js",
@@ -1870,8 +1870,8 @@
18701870
"end":22
18711871
},
18721872
{
1873-
"raw_type":"{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"\"\n },\n \"kind\":\"EmptyT\"\n}",
1874-
"type":"",
1873+
"raw_type":"{\n \"reason\":{\n \"pos\":{\n \"source\":null,\n \"type\":null,\n \"start\":{\"line\":0,\"column\":1,\"offset\":0},\n \"end\":{\"line\":0,\"column\":0,\"offset\":0}\n },\n \"desc\":\"empty\"\n },\n \"kind\":\"EmptyT\"\n}",
1874+
"type":"empty",
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"reasons":[],
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"loc":{
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"source":"test.js",
@@ -2173,7 +2173,7 @@
21732173
"end":50
21742174
},
21752175
{
2176-
"desc":"",
2176+
"desc":"empty",
21772177
"loc":{
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"source":"test.js",
21792179
"type":"SourceFile",
@@ -2187,7 +2187,7 @@
21872187
"end":50
21882188
},
21892189
{
2190-
"desc":"",
2190+
"desc":"empty",
21912191
"loc":{
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"source":"test.js",
21932193
"type":"SourceFile",
@@ -2201,7 +2201,7 @@
22012201
"end":50
22022202
},
22032203
{
2204-
"desc":"",
2204+
"desc":"empty",
22052205
"loc":{
22062206
"source":"test.js",
22072207
"type":"SourceFile",
@@ -2215,7 +2215,7 @@
22152215
"end":50
22162216
},
22172217
{
2218-
"desc":"",
2218+
"desc":"empty",
22192219
"loc":{
22202220
"source":"test.js",
22212221
"type":"SourceFile",
@@ -2374,7 +2374,7 @@
23742374
"end":34
23752375
},
23762376
{
2377-
"desc":"",
2377+
"desc":"empty",
23782378
"loc":{
23792379
"source":"test.js",
23802380
"type":"SourceFile",

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