[flow][name-def] pass "conditional" context to more expressions in co…

…nditional positions

Summary:
In upcoming on natural inference, we need to determine if a primitive literals or variables appears in a context where increased precision is necessary.

Consider for example the code
```
const one = 1;
declare var x: number;
if (x === one) {
  x as 1; // okay
}
```
The position of `one` in the conditional needs to be considered as high precision, in other words we'd like to infer the instance of `one` there as `1` instead of `number`. This will allow the behavior of actually refining `x` to also be `1` and thus allow the cast, like we do today.

This diff achieves this by pass a "conditional" context to a few more cases in Name_def:
* members of the binary expression in `visit_binary_expression`
* switch statement cases

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D70640801

fbshipit-source-id: 34d7cbdc3e04e7f5c63d9713e79f41f01e7a40f4

src/analysis/env_builder/name_def.ml

@@ -2993,16 +2993,16 @@ class def_finder ~autocomplete_hooks ~react_jsx env_info toplevel_scope =
             ignore @@ this#expression value)
           ~on_member_eq_other:(fun expr value ->
             this#visit_expression ~hints:[] ~cond expr;
-            ignore @@ this#expression value)
+            this#visit_expression ~hints:[] ~cond value)
           ~on_other_eq_member:(fun value expr ->
             this#visit_expression ~hints:[] ~cond expr;
-            ignore @@ this#expression value)
+            this#visit_expression ~hints:[] ~cond value)
           ~is_switch_cond_context:false
           ~strict:false
           ~sense:false
           ~on_other_eq_test:(fun left right ->
-            ignore @@ this#expression left;
-            ignore @@ this#expression right)
+            ignore @@ this#visit_expression ~hints:[] ~cond left;
+            ignore @@ this#visit_expression ~hints:[] ~cond right)
           ALoc.none
           left
           right
@@ -3148,6 +3148,13 @@ class def_finder ~autocomplete_hooks ~react_jsx env_info toplevel_scope =
       );
       res
 
+    method! switch_case case =
+      let open Ast.Statement.Switch.Case in
+      let (_loc, { test; consequent; comments = _ }) = case in
+      Base.Option.iter ~f:(this#visit_expression ~hints:[] ~cond:OtherConditionalTest) test;
+      ignore @@ this#statement_list consequent;
+      case
+
     method! match_expression loc _ = fail loc "Should be visited by visit_match_expression"
 
     method private visit_match_expression ~hints x =