[flow] add a new IndexContext case to Type.enclosing_context

Summary:
* Makes the context of `x` in `o[x]` a special kind of context (`IndexContext`). This flag is now passed alongside the existing conditional context(`cond` parameter), so that it can be used under natural inference to infer more precise types for primitive literals.
* Propagates `cond` flag to a few more expressions in statement.ml (e.g. pattern match cases)

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D70676102

fbshipit-source-id: e29765b12473dbdbf7e33d5fb3f3d245b7787312

src/services/autocomplete/autocomplete_js.ml

@@ -162,7 +162,7 @@ module Inference = struct
   let type_of_match_member_pattern cx loc mem =
     Match_pattern.type_of_member_pattern
       cx
-      ~on_identifier:(Statement.identifier ~encl_ctx:Type.NoContext)
+      ~on_identifier:Statement.identifier
       ~on_expression:Statement.expression
       (loc, mem)
 end

src/typing/match_pattern.ml

@@ -95,7 +95,7 @@ let rec member cx ~on_identifier ~on_expression mem =
     match base with
     | BaseIdentifier (loc, id) ->
       let exp = (loc, Ast.Expression.Identifier (loc, id)) in
-      (exp, BaseIdentifier ((loc, on_identifier cx id loc), id))
+      (exp, BaseIdentifier ((loc, on_identifier ~encl_ctx:Type.OtherTest cx id loc), id))
     | BaseMember mem ->
       let (exp, mem) = member cx ~on_identifier ~on_expression mem in
       (exp, BaseMember mem)
@@ -179,7 +179,7 @@ let rec pattern_ cx ~on_identifier ~on_expression ~on_binding ~in_or_pattern acc
       in
       AsPattern { AsPattern.pattern = p; target; comments }
     | IdentifierPattern (loc, x) ->
-      let t = on_identifier cx x loc in
+      let t = on_identifier ~encl_ctx:Type.OtherTest cx x loc in
       IdentifierPattern ((loc, t), x)
     | BindingPattern x -> BindingPattern (binding_pattern cx ~on_binding ~in_or_pattern ~loc acc x)
     | WildcardPattern x -> WildcardPattern x

src/typing/match_pattern.mli

@@ -9,7 +9,8 @@ module Ast = Flow_ast
 
 val pattern :
   Context.t ->
-  on_identifier:(Context.t -> ALoc.t Ast.Identifier.t' -> ALoc.t -> Type.t) ->
+  on_identifier:
+    (encl_ctx:Type.enclosing_context -> Context.t -> ALoc.t Ast.Identifier.t' -> ALoc.t -> Type.t) ->
   on_expression:
     (Context.t -> (ALoc.t, ALoc.t) Ast.Expression.t -> (ALoc.t, ALoc.t * Type.t) Ast.Expression.t) ->
   on_binding:
@@ -20,7 +21,8 @@ val pattern :
 
 val type_of_member_pattern :
   Context.t ->
-  on_identifier:(Context.t -> ALoc.t Ast.Identifier.t' -> ALoc.t -> Type.t) ->
+  on_identifier:
+    (encl_ctx:Type.enclosing_context -> Context.t -> ALoc.t Ast.Identifier.t' -> ALoc.t -> Type.t) ->
   on_expression:
     (Context.t -> (ALoc.t, ALoc.t) Ast.Expression.t -> (ALoc.t, ALoc.t * Type.t) Ast.Expression.t) ->
   (ALoc.t, ALoc.t) Ast.MatchPattern.MemberPattern.t ->

src/typing/statement.ml

@@ -1221,7 +1221,8 @@ module Make
                     Flow_ast.Expression.Identifier (Flow_ast_utils.match_root_ident case_loc)
                   )
                   pattern
-                  ~on_identifier:(fun cx -> identifier cx empty_syntactic_flags)
+                  ~on_identifier:(fun ~encl_ctx cx ->
+                    identifier cx { empty_syntactic_flags with Primitive_literal.encl_ctx })
                   ~on_expression:expression
                   ~on_binding:(fun ~use_op ~name_loc ~kind name t ->
                     init_var kind cx ~use_op t name_loc;
@@ -2493,7 +2494,7 @@ module Make
                     shorthand;
                   }
               ) ->
-            let (((_, kt), _) as k') = expression cx k in
+            let (((_, kt), _) as k') = expression cx ~encl_ctx:IndexContext k in
             let (((_, vt), _) as v') = expression cx ~as_const v in
             let computed = mk_computed k kt vt in
             ( ObjectExpressionAcc.add_computed cx computed acc,
@@ -2516,7 +2517,7 @@ module Make
                     value = (fn_loc, fn);
                   }
               ) ->
-            let (((_, kt), _) as k') = expression cx k in
+            let (((_, kt), _) as k') = expression cx ~encl_ctx:IndexContext k in
             let ((_, vt), v') = expression cx (fn_loc, Ast.Expression.Function fn) in
             let fn =
               match v' with
@@ -2946,7 +2947,8 @@ module Make
                   cx
                   (case_loc, Identifier (Flow_ast_utils.match_root_ident case_loc))
                   pattern
-                  ~on_identifier:(fun cx -> identifier cx empty_syntactic_flags)
+                  ~on_identifier:(fun ~encl_ctx cx ->
+                    identifier cx { empty_syntactic_flags with Primitive_literal.encl_ctx })
                   ~on_expression:expression
                   ~on_binding:(fun ~use_op ~name_loc ~kind name t ->
                     init_var kind cx ~use_op t name_loc;
@@ -4539,7 +4541,7 @@ module Make
           )
         in
         let eval_index () =
-          let (((_, tind), _) as index) = expression cx index in
+          let (((_, tind), _) as index) = expression ~encl_ctx:IndexContext cx index in
           (tind, index)
         in
         let conf =
@@ -4836,7 +4838,7 @@ module Make
               )
             in
             let eval_args_and_expr () =
-              let (((_, elem_t), _) as expr) = expression cx expr in
+              let (((_, elem_t), _) as expr) = expression ~encl_ctx:IndexContext cx expr in
               let (argts, arguments_ast) = arg_list cx arguments in
               ((argts, elem_t), (arguments_ast, expr))
             in
@@ -4973,7 +4975,8 @@ module Make
         | SwitchTest _
         | OtherTest ->
           BoolModuleT.at loc
-        | NoContext ->
+        | NoContext
+        | IndexContext ->
           let reason = mk_reason (RUnaryOperator ("not", desc_of_t arg)) loc in
           Operators.unary_not cx reason arg
       in
@@ -5074,7 +5077,9 @@ module Make
   and visit_eq_test cx ~encl_ctx loc left right =
     let check ~encl_ctx = expression cx ~encl_ctx in
     match encl_ctx with
-    | NoContext -> check ~encl_ctx:NoContext
+    | NoContext
+    | IndexContext ->
+      check ~encl_ctx
     | SwitchTest _
     | OtherTest ->
       let reconstruct_ast = check ~encl_ctx:OtherTest in
@@ -5142,7 +5147,9 @@ module Make
       let (((_, t2), _) as right) = reconstruct_ast right in
       begin
         match encl_ctx with
-        | NoContext -> ()
+        | NoContext
+        | IndexContext ->
+          ()
         | SwitchTest _
         | OtherTest ->
           matching_prop_check cx left right;
@@ -5452,7 +5459,7 @@ module Make
       let reason = mk_reason (RPropertyAssignment None) lhs_loc in
       let lhs_reason = mk_expression_reason _object in
       let (o, _object) = typecheck_object _object in
-      let (((_, i), _) as index) = expression cx index in
+      let (((_, i), _) as index) = expression ~encl_ctx:IndexContext cx index in
       let use_op = make_op ~lhs:reason ~prop:(mk_reason (desc_of_reason lhs_prop_reason) iloc) in
       let upper = maybe_chain lhs_reason (SetElemT (use_op, reason, i, mode, t, None)) in
       Flow.flow cx (o, upper);
@@ -6471,7 +6478,8 @@ module Make
     | SwitchTest _
     | OtherTest ->
       OptTestPropT (use_op, reason, id, mk_named_prop ~reason:prop_reason prop_name, hint)
-    | NoContext ->
+    | NoContext
+    | IndexContext ->
       OptGetPropT
         {
           use_op;

src/typing/type.ml

@@ -897,6 +897,8 @@ module rec TypeTerm : sig
       }
     (* `if(C){}`, `while(C){}`, `C?e1:e2`, `invariant(C)`, ... *)
     | OtherTest
+    (* `o[C]`, `o[C]=e`, `{[C]:e}`, `o[C]()` *)
+    | IndexContext
 
   (* Bindings created from destructuring annotations should themselves act like
    * annotations. That is, `var {p}: {p: string}; p = 0` should be an error,

src/typing/type_operation_utils.ml

@@ -256,6 +256,7 @@ module Operators = struct
                 explanation = None;
               }
           | NoContext
+          | IndexContext
           | OtherTest ->
             let reasons = FlowError.ordered_reasons (reason_of_t l, reason_of_t r) in
             Error_message.EComparison reasons)
@@ -282,6 +283,7 @@ module Operators = struct
         match encl_ctx with
         | SwitchTest _ -> Some (Lazy.force comparison_error)
         | NoContext
+        | IndexContext
         | OtherTest ->
           None
       end