[flow] Test showing duplicated errors on indexed object subtyping

Summary:
I'd like to make an improvement to these errors so that we only emit the value-side errors if the key check already passes. Showing the bad error behavior with a test in this diff. The additional errors provide very little value.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D69023898

fbshipit-source-id: f4a5044c12846ae3c14e6d8a26d2343325146d49

tests/indexed_objects/indexed_objects.exp

@@ -1 +1,39 @@
-Found 0 errors
+Error ---------------------------------------------------------------------------------------------------- test.js:15:23
+
+Cannot assign object literal to `error1` because string `foo` [1] is incompatible with string prefixed with `data-` [2]
+in the indexer property's key. [incompatible-type]
+
+   test.js:15:23
+   15| const error1: Props = {foo: 3};
+                             ^^^^^^^^ [1]
+
+References:
+   test.js:11:4
+   11|   [StringPrefix<'data-'>]: string | void,
+          ^^^^^^^^^^^^^^^^^^^^^ [2]
+
+
+Error ---------------------------------------------------------------------------------------------------- test.js:15:29
+
+Cannot assign object literal to `error1` because in property `foo`: [incompatible-type]
+ - Either number [1] is incompatible with string [2].
+ - Or number [1] is incompatible with undefined [3].
+
+   test.js:15:29
+   15| const error1: Props = {foo: 3};
+                                   ^ [1]
+
+References:
+   test.js:11:28
+   11|   [StringPrefix<'data-'>]: string | void,
+                                  ^^^^^^ [2]
+   test.js:11:37
+   11|   [StringPrefix<'data-'>]: string | void,
+                                           ^^^^ [3]
+
+
+
+Found 2 errors
+
+Only showing the most relevant union/intersection branches.
+To see all branches, re-run Flow with --show-all-branches

tests/indexed_objects/test.js

@@ -6,3 +6,10 @@ const y: Y = {foo: 3}; // No error
 
 type Z = $Exact<{[string]: number}>;
 const z: Z = {foo: 3}; // No error
+
+type Props = {
+  [StringPrefix<'data-'>]: string | void,
+}
+
+// TODO: Combine errors
+const error1: Props = {foo: 3};