From 447a2529bca8e3c635333f723137a20bd8a0c450 Mon Sep 17 00:00:00 2001
From: George Zahariev <gkz@meta.com>
Date: Tue, 7 Jan 2025 14:29:50 -0800
Subject: [PATCH] [flow][match] Fix match refinement of arrays with tuple views

Summary:
One day natural inference will mean we don't need to think about this, but until then we need to handle it.

Array literals initialized with some values act as a tuple. Handle them like we handle tuples.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D67778713

fbshipit-source-id: a2b7bad3c8a02874027f82e2712cf797adc19275
---
 src/typing/type_filter.ml | 7 ++++++-
 tests/match/patterns.js   | 9 +++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/typing/type_filter.ml b/src/typing/type_filter.ml
index 3fcffa773c9..102ba3de8e8 100644
--- a/src/typing/type_filter.ml
+++ b/src/typing/type_filter.ml
@@ -599,7 +599,12 @@ let not_array t =
 
 let array_length ~sense ~op ~n t =
   match t with
-  | DefT (_, ArrT (TupleAT { arity = (num_req, num_total); inexact; _ })) ->
+  | DefT (_, ArrT (TupleAT { arity = (num_req, num_total); inexact; _ }))
+  | DefT
+      ( _,
+        ArrT
+          (ArrayAT { tuple_view = Some (TupleView { arity = (num_req, num_total); inexact; _ }); _ })
+      ) ->
     (* `None` represents "maybe" a match *)
     let matches =
       match op with
diff --git a/tests/match/patterns.js b/tests/match/patterns.js
index 51a6caffa62..b745aa79571 100644
--- a/tests/match/patterns.js
+++ b/tests/match/patterns.js
@@ -160,3 +160,12 @@
     _: 0,
   };
 }
+
+// Array pattern applied to array literal
+{
+  const x = [1, 'foo'];
+
+  const out = match (x) {
+    [_, const b]: b as string, // OK
+  };
+}