[flow] add experimental.natural_inference.local_primitive_literals option

Summary:
Adds a flag that will enable the new behavior of natural inference on primitive literals and const-vars initialized with primitive literals.

The valid values of the `experimental.natural_inference.local_primitive_literals` flowconfig option enable a two phase rollout for this behavior:
* "partial" mode enables precise inference (singleton literal types) for literals/const-variables when necessary (e.g. in the presence of annotations, `as const`, etc.)
* "full" mode additionally enables general types (`StrGeneralT`, etc.) to be inferred for literals/const-variables otherwise (instead of `StrT_UNSOUND`, etc. that is inferred today)

Changelog: [internal]

Reviewed By: gkz

Differential Revision: D70712087

fbshipit-source-id: 757ff37a87669803a1a1cc817cabbb76a8927dcc

Author: panagosg7

src/commands/commandUtils.ml

@@ -1464,6 +1464,8 @@ let make_options
     opt_strict_mode = strict_mode;
     opt_merge_timeout;
     opt_missing_module_generators = FlowConfig.missing_module_generators flowconfig;
+    opt_natural_inference_exports_primitive_const =
+      FlowConfig.natural_inference_local_primitive_literals flowconfig;
     opt_no_unchecked_indexed_access = FlowConfig.no_unchecked_indexed_access flowconfig;
     opt_saved_state_fetcher;
     opt_saved_state_force_recheck = saved_state_options_flags.saved_state_force_recheck;

src/commands/config/flowConfig.ml

@@ -113,6 +113,7 @@ module Opts = struct
     multi_platform_extension_group_mapping: (string * string list) list;
     multi_platform_ambient_supports_platform_directory_overrides: (string * string list) list;
     munge_underscores: bool;
+    natural_inference_local_primitive_literals: Options.NaturalInferenceLevel.t;
     no_flowlib: bool;
     no_unchecked_indexed_access: bool;
     node_main_fields: string list;
@@ -250,6 +251,7 @@ module Opts = struct
       multi_platform_extension_group_mapping = [];
       multi_platform_ambient_supports_platform_directory_overrides = [];
       munge_underscores = false;
+      natural_inference_local_primitive_literals = Options.NaturalInferenceLevel.Off;
       no_flowlib = false;
       no_unchecked_indexed_access = false;
       node_main_fields = ["main"];
@@ -1124,6 +1126,15 @@ module Opts = struct
       ("module.use_strict", boolean (fun opts v -> Ok { opts with modules_are_use_strict = v }));
       ("munge_underscores", boolean (fun opts v -> Ok { opts with munge_underscores = v }));
       ("name", root_name_parser);
+      ( "experimental.natural_inference.local_primitive_literals",
+        enum
+          [
+            ("off", Options.NaturalInferenceLevel.Off);
+            ("partial", Options.NaturalInferenceLevel.Partial);
+            ("full", Options.NaturalInferenceLevel.Full);
+          ]
+          (fun opts v -> Ok { opts with natural_inference_local_primitive_literals = v })
+      );
       ("no_flowlib", boolean (fun opts v -> Ok { opts with no_flowlib = v }));
       ( "no_unchecked_indexed_access",
         boolean (fun opts v -> Ok { opts with no_unchecked_indexed_access = v })
@@ -1894,6 +1905,9 @@ let multi_platform_ambient_supports_platform_directory_overrides c =
 
 let munge_underscores c = c.options.Opts.munge_underscores
 
+let natural_inference_local_primitive_literals c =
+  c.options.Opts.natural_inference_local_primitive_literals
+
 let no_flowlib c = c.options.Opts.no_flowlib
 
 let no_unchecked_indexed_access c = c.options.Opts.no_unchecked_indexed_access

src/commands/config/flowConfig.mli

@@ -208,6 +208,8 @@ val multi_platform_ambient_supports_platform_directory_overrides :
 
 val munge_underscores : config -> bool
 
+val natural_inference_local_primitive_literals : config -> Options.NaturalInferenceLevel.t
+
 val no_flowlib : config -> bool
 
 val no_unchecked_indexed_access : config -> bool

src/common/options.ml

@@ -42,6 +42,13 @@ type react_rules =
   | DeepReadOnlyHookReturns
   | RulesOfHooks
 
+module NaturalInferenceLevel = struct
+  type t =
+    | Off
+    | Partial
+    | Full
+end
+
 type format = {
   opt_bracket_spacing: bool;
   opt_single_quotes: bool;
@@ -128,6 +135,7 @@ type t = {
   opt_module_name_mappers: (Str.regexp * string) list;
   opt_modules_are_use_strict: bool;
   opt_munge_underscores: bool;
+  opt_natural_inference_exports_primitive_const: NaturalInferenceLevel.t;
   opt_no_unchecked_indexed_access: bool;
   opt_node_main_fields: string list;
   opt_node_package_export_conditions: string list;
@@ -302,6 +310,9 @@ let module_system opts = opts.opt_module
 
 let modules_are_use_strict opts = opts.opt_modules_are_use_strict
 
+let natural_inference_local_primitive_literals opts =
+  opts.opt_natural_inference_exports_primitive_const
+
 let no_unchecked_indexed_access opts = opts.opt_no_unchecked_indexed_access
 
 let node_main_fields opts = opts.opt_node_main_fields

src/flow_dot_js.ml

@@ -125,6 +125,7 @@ let stub_metadata ~root ~checked =
     max_literal_length = 100;
     max_workers = 0;
     missing_module_generators = [];
+    natural_inference_local_primitive_literals = Options.NaturalInferenceLevel.Off;
     no_unchecked_indexed_access = false;
     react_custom_jsx_typing = false;
     react_ref_as_prop = Options.ReactRefAsProp.PartialSupport;

src/services/code_action/__tests__/refactor_extract_utils_tests.ml

@@ -53,6 +53,7 @@ let stub_metadata ~root ~checked =
     max_literal_length = 100;
     max_workers = 0;
     missing_module_generators = [];
+    natural_inference_local_primitive_literals = Options.NaturalInferenceLevel.Off;
     no_unchecked_indexed_access = false;
     react_custom_jsx_typing = false;
     react_ref_as_prop = Options.ReactRefAsProp.PartialSupport;

src/typing/__tests__/type_hint_test.ml

@@ -48,6 +48,7 @@ let metadata =
     max_literal_length = 100;
     max_workers = 0;
     missing_module_generators = [];
+    natural_inference_local_primitive_literals = Options.NaturalInferenceLevel.Off;
     no_unchecked_indexed_access = false;
     react_custom_jsx_typing = false;
     react_ref_as_prop = Options.ReactRefAsProp.PartialSupport;

src/typing/__tests__/typed_ast_test.ml

@@ -46,6 +46,7 @@ let metadata =
     max_literal_length = 100;
     max_workers = 0;
     missing_module_generators = [];
+    natural_inference_local_primitive_literals = Options.NaturalInferenceLevel.Off;
     no_unchecked_indexed_access = false;
     react_custom_jsx_typing = false;
     react_ref_as_prop = Options.ReactRefAsProp.PartialSupport;

src/typing/context.ml

@@ -57,6 +57,7 @@ type metadata = {
   max_literal_length: int;
   max_workers: int;
   missing_module_generators: (Str.regexp * string) list;
+  natural_inference_local_primitive_literals: Options.NaturalInferenceLevel.t;
   no_unchecked_indexed_access: bool;
   react_custom_jsx_typing: bool;
   react_ref_as_prop: Options.ReactRefAsProp.t;
@@ -290,6 +291,8 @@ let metadata_of_options options =
     max_literal_length = Options.max_literal_length options;
     max_workers = Options.max_workers options;
     missing_module_generators = Options.missing_module_generators options;
+    natural_inference_local_primitive_literals =
+      Options.natural_inference_local_primitive_literals options;
     no_unchecked_indexed_access = Options.no_unchecked_indexed_access options;
     react_custom_jsx_typing = Options.react_custom_jsx_typing options;
     react_ref_as_prop = Options.react_ref_as_prop options;
@@ -663,6 +666,20 @@ let max_workers cx = cx.metadata.max_workers
 
 let missing_module_generators cx = cx.metadata.missing_module_generators
 
+let natural_inference_local_primitive_literals_partial cx =
+  match cx.metadata.natural_inference_local_primitive_literals with
+  | Options.NaturalInferenceLevel.Off -> false
+  | Options.NaturalInferenceLevel.Partial
+  | Options.NaturalInferenceLevel.Full ->
+    true
+
+let natural_inference_local_primitive_literals_full cx =
+  match cx.metadata.natural_inference_local_primitive_literals with
+  | Options.NaturalInferenceLevel.Off
+  | Options.NaturalInferenceLevel.Partial ->
+    false
+  | Options.NaturalInferenceLevel.Full -> true
+
 let no_unchecked_indexed_access cx = cx.metadata.no_unchecked_indexed_access
 
 let jsx cx = cx.metadata.jsx

src/typing/context.mli

@@ -107,6 +107,7 @@ type metadata = {
   max_literal_length: int;
   max_workers: int;
   missing_module_generators: (Str.regexp * string) list;
+  natural_inference_local_primitive_literals: Options.NaturalInferenceLevel.t;
   no_unchecked_indexed_access: bool;
   react_custom_jsx_typing: bool;
   react_ref_as_prop: Options.ReactRefAsProp.t;
@@ -317,6 +318,10 @@ val max_workers : t -> int
 
 val missing_module_generators : t -> (Str.regexp * string) list
 
+val natural_inference_local_primitive_literals_partial : t -> bool
+
+val natural_inference_local_primitive_literals_full : t -> bool
+
 val no_unchecked_indexed_access : t -> bool
 
 val jsx : t -> Options.jsx_mode