From 10d4393443eba108d674d1ecbde5a8144d75478c Mon Sep 17 00:00:00 2001
From: George Zahariev <gkz@meta.com>
Date: Tue, 10 Dec 2024 10:53:41 -0800
Subject: [PATCH] [flow] Update how `typeof x === 'object'` on `typeof x ===
 'function'` is empty

Summary: Changelog: [errors] If you have refiend a value based on `typeof x === 'function'`, and then do `typeof x === 'object'`, the result is now `empty` as that is impossible.

Reviewed By: SamChou19815

Differential Revision: D67031335

fbshipit-source-id: e0c11ddec6cc2dfc71000c600dab882fab6e3489
---
 src/typing/type_filter.ml         |  2 +-
 tests/refinements/mixed.js        |  9 +++++++++
 tests/refinements/refinements.exp | 33 ++++++++++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/src/typing/type_filter.ml b/src/typing/type_filter.ml
index 75b6dbf1b7e..9d1f5be35b9 100644
--- a/src/typing/type_filter.ml
+++ b/src/typing/type_filter.ml
@@ -522,7 +522,7 @@ let rec object_ cx t =
       | Mixed_non_maybe
       | Mixed_non_null ->
         obj |> changed_result
-      | Mixed_function
+      | Mixed_function -> DefT (reason_of_t t, EmptyT) |> changed_result
       | Mixed_everything
       | Mixed_non_void ->
         let reason = replace_desc_new_reason RUnion (reason_of_t t) in
diff --git a/tests/refinements/mixed.js b/tests/refinements/mixed.js
index 2014624bb06..e4fa67d677f 100644
--- a/tests/refinements/mixed.js
+++ b/tests/refinements/mixed.js
@@ -128,3 +128,12 @@ const loop = (condition: boolean) => {
     }
   }
 };
+
+{
+  declare const x: mixed;
+  if (typeof x === 'function') {
+    if (typeof x === 'object') {
+      x as empty; // OK: Impossible to be both
+    }
+  }
+}
diff --git a/tests/refinements/refinements.exp b/tests/refinements/refinements.exp
index 5b99052c014..1494923531e 100644
--- a/tests/refinements/refinements.exp
+++ b/tests/refinements/refinements.exp
@@ -9330,6 +9330,37 @@ References:
                 ^^^^^^^^^^^^^^^^^^^ [1]
 
 
+Error -------------------------------------------------------------------------------------------------- mixed.js:135:16
+
+Refined at [1]
+
+   mixed.js:135:16
+   135|     if (typeof x === 'object') {
+                       ^
+
+References:
+   mixed.js:134:7
+   134|   if (typeof x === 'function') {
+              ^^^^^^^^^^^^^^^^^^^^^^^ [1]
+
+
+Error --------------------------------------------------------------------------------------------------- mixed.js:136:7
+
+Refined at [1] [2]
+
+   mixed.js:136:7
+   136|       x as empty; // OK: Impossible to be both
+              ^
+
+References:
+   mixed.js:134:7
+   134|   if (typeof x === 'function') {
+              ^^^^^^^^^^^^^^^^^^^^^^^ [1]
+   mixed.js:135:9
+   135|     if (typeof x === 'object') {
+                ^^^^^^^^^^^^^^^^^^^^^ [2]
+
+
 Error --------------------------------------------------------------------------------------------- mixed_object.js:2:32
 
 Refined at [1]
@@ -17001,7 +17032,7 @@ References:
 
 
 
-Found 1155 errors
+Found 1157 errors
 
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