[flow][tuples] Allow tuple type spread of tuple-like arrays

Summary:
Changelog: [internal]
Allow tuple type spread of tuple-like arrays. This is required for the next diff to work - reversal of tuple type spread.

Reviewed By: SamChou19815

Differential Revision: D55721534

fbshipit-source-id: e856bf2965ade26bc201782fe8da5d62cacc4d8b

Author: gkz

src/typing/flow_js.ml

@@ -2238,7 +2238,7 @@ struct
             | DefT (_, ArrT arrtype) ->
               (* Arrays *)
               (match (rrt_resolve_to, arrtype) with
-              | (ResolveSpreadsToTupleType _, (ArrayAT _ | ROArrayAT _)) ->
+              | (ResolveSpreadsToTupleType _, (ArrayAT { tuple_view = None; _ } | ROArrayAT _)) ->
                 (* Only tuples can be spread into tuple types. *)
                 add_output
                   cx

tests/tuples/spread.js

@@ -54,6 +54,11 @@ type ArraySpread = [...Array<mixed>]; // ERROR
   declare const x: ArraySpread;
   x as empty; // OK
 }
+type ROArraySpread = [...$ReadOnlyArray<mixed>]; // ERROR
+{
+  declare const x: ROArraySpread;
+  x as empty; // OK
+}
 
 // Spreading `any`
 type AnySpread = [1, 2, ...any]; // OK
@@ -69,6 +74,13 @@ type EmptySpread = [1, 2, ...empty]; // OK
   x as empty; // OK
 }
 
+// Tuple-like array spread
+{
+  const x = [1, 2];
+  type TupleArrSpread = [0, ...typeof x]; // OK
+  [0, 1, 2] as TupleArrSpread; // OK
+}
+
 // Generics
 type WithTail<T> = [1, ...T];
 [1, 2, 3] as WithTail<[2, 3]>; // OK

tests/tuples/tuples.exp

@@ -1182,36 +1182,50 @@ References:
                               ^^^^^^^^^^^^ [1]
 
 
-Error --------------------------------------------------------------------------------------------------- spread.js:75:8
+Error -------------------------------------------------------------------------------------------------- spread.js:57:22
+
+Cannot spread non-tuple (read-only array type [1]) into tuple type. [tuple-invalid-type-spread]
+
+   spread.js:57:22
+   57| type ROArraySpread = [...$ReadOnlyArray<mixed>]; // ERROR
+                            ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+References:
+   spread.js:57:26
+   57| type ROArraySpread = [...$ReadOnlyArray<mixed>]; // ERROR
+                                ^^^^^^^^^^^^^^^^^^^^^ [1]
+
+
+Error --------------------------------------------------------------------------------------------------- spread.js:87:8
 
 Cannot cast array literal to `WithTail` because number [1] is incompatible with number literal `3` [2] in index 2.
 [incompatible-cast]
 
-   spread.js:75:8
-   75| [1, 2, 66] as WithTail<[2, 3]>; // ERROR
+   spread.js:87:8
+   87| [1, 2, 66] as WithTail<[2, 3]>; // ERROR
               ^^ [1]
 
 References:
-   spread.js:75:28
-   75| [1, 2, 66] as WithTail<[2, 3]>; // ERROR
+   spread.js:87:28
+   87| [1, 2, 66] as WithTail<[2, 3]>; // ERROR
                                   ^ [2]
 
 
-Error --------------------------------------------------------------------------------------------------- spread.js:78:1
+Error --------------------------------------------------------------------------------------------------- spread.js:90:1
 
 Cannot call `f` because `T` [1] is underconstrained by call of `f` [2]. Either add explicit type arguments or cast the
 expression to your expected type. [underconstrained-implicit-instantiation]
 
-   spread.js:78:1
-   78| f([1, 2, 3]); // ERROR: annotation required - reversal not yet implemented
+   spread.js:90:1
+   90| f([1, 2, 3]); // ERROR: annotation required - reversal not yet implemented
        ^
 
 References:
-   spread.js:77:20
-   77| declare function f<T>(xs: [1, ...T]): void;
+   spread.js:89:20
+   89| declare function f<T>(xs: [1, ...T]): void;
                           ^ [1]
-   spread.js:78:1
-   78| f([1, 2, 3]); // ERROR: annotation required - reversal not yet implemented
+   spread.js:90:1
+   90| f([1, 2, 3]); // ERROR: annotation required - reversal not yet implemented
        ^^^^^^^^^^^^ [2]
 
 
@@ -1984,4 +1998,4 @@ References:
 
 
 
-Found 124 errors
+Found 125 errors