[flow] Specialized implementation for identifier type synthesis in cl…

…ass extends

Summary:
The extends clause in class, although being an expression, is more annotation-like. We made this decision during LTI development so that we can tolerate more cyclic class definitions in the most common cases.

In the LTI 2.0 system, all the annotations will be resolved lazily all at once at the end of component resolution. Early forcing is not allowed, otherwise it will result in internal error. Currently, class extends' identifier are evaluated eagarly due to repositioning. We can achieve the same using AnnotT, and avoid the eagar repositioning. Using AnnotT to achieve repositioning effect is already used extensively in type_annotation and type_sig_merge when we are refering to a type identifier.

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D55296799

fbshipit-source-id: d9d035750e81d58eca4befdf1f947719779187f0

src/typing/statement.ml

@@ -6490,8 +6490,8 @@ module Make
           let open Ast.Expression in
           let rec super_expr (loc, expr) =
             match expr with
-            | Identifier (id_loc, id) ->
-              let t = identifier cx id id_loc in
+            | Identifier (id_loc, ({ Ast.Identifier.name; comments = _ } as id)) ->
+              let t = Type_env.sig_var_ref cx (OrdinaryName name) id_loc in
               (t, (fun () -> ((loc, t), Identifier ((id_loc, t), id))))
             | Member
                 {

src/typing/type_env.ml

@@ -675,6 +675,15 @@ let var_ref ?(lookup_mode = ForValue) cx ?desc name loc =
   let t = query_var ~lookup_mode cx name ?desc loc in
   Flow_js.reposition cx loc t
 
+let sig_var_ref ?(lookup_mode = ForValue) cx ?desc name loc =
+  let desc =
+    match desc with
+    | Some desc -> desc
+    | None -> RIdentifier name
+  in
+  let reason = mk_reason desc loc in
+  AnnotT (reason, query_var cx ~lookup_mode name loc, true)
+
 let read_class_self_type cx loc =
   match checked_find_loc_env_write_opt cx Env_api.ClassSelfLoc loc with
   | Some t -> t

src/typing/type_env.mli

@@ -118,6 +118,14 @@ val var_ref :
   ALoc.t ->
   Type.t
 
+val sig_var_ref :
+  ?lookup_mode:LookupMode.t ->
+  Context.t ->
+  ?desc:Reason.reason_desc ->
+  Reason.name ->
+  ALoc.t ->
+  Type.t
+
 val intrinsic_ref :
   Context.t -> ?desc:Reason.reason_desc -> Reason.name -> ALoc.t -> (Type.t * ALoc.t) option
 

tests/autocomplete/autocomplete.exp

@@ -2679,6 +2679,10 @@ class_declaration_name.js:5:8
 Flags: --pretty
 {"result":[]}
 
+class_extends.js:5:20
+Flags: --pretty
+{"result":[{"name":"Foo","type":"class Foo"},{"name":"function","type":""}]}
+
 pattern_object_key_middle.js:6:12
 Flags: --pretty
 {"result":[{"name":"foobar","type":"string"}]}

tests/autocomplete/class_extends.js

@@ -0,0 +1,6 @@
+// @flow
+
+class Foo {}
+
+class Bar extends F
+//                 ^

tests/autocomplete/test.sh

@@ -76,6 +76,7 @@ queries_in_file autocomplete "enums.js" --lsp
 queries_in_file autocomplete "enum-key.js" --lsp
 queries_in_file autocomplete "enum-id.js" --pretty
 queries_in_file autocomplete "class_declaration_name.js" --pretty
+queries_in_file autocomplete "class_extends.js" --pretty
 queries_in_file autocomplete "pattern_object_key_middle.js" --pretty
 queries_in_file autocomplete "iterator.js" --lsp
 queries_in_file autocomplete "indexed-access-1.js" --lsp

tests/extends/extends.exp

@@ -14,19 +14,16 @@ References:
 
 Error ---------------------------------------------------------------------------------------------------- test.js:30:17
 
-Cannot extend `D` [1] with `obj` because object type [2] is not inheritable. [incompatible-use]
+Cannot extend `D` [1] with `obj` because `obj` [2] is not inheritable. [incompatible-use]
 
    test.js:30:17
    30| class D extends obj {}
-                       ^^^
+                       ^^^ [2]
 
 References:
    test.js:30:7
    30| class D extends obj {}
              ^ [1]
-   test.js:29:18
-   29| declare var obj: {};
-                        ^^ [2]
 
 
 

tests/rec/rec.exp

@@ -339,20 +339,17 @@ References:
 
 Error ----------------------------------------------------------------------------------------------- this_subst.js:1:53
 
-Cannot extend `InstrumentedContainer` [1] with `container` because uninitialized variable [2] is not inheritable.
+Cannot extend `InstrumentedContainer` [1] with `container` because `container` [2] is not inheritable.
 [incompatible-use]
 
    this_subst.js:1:53
    1| var container = class InstrumentedContainer extends container {
-                                                          ^^^^^^^^^
+                                                          ^^^^^^^^^ [2]
 
 References:
    this_subst.js:1:23
    1| var container = class InstrumentedContainer extends container {
                             ^^^^^^^^^^^^^^^^^^^^^ [1]
-   this_subst.js:1:5
-   1| var container = class InstrumentedContainer extends container {
-          ^^^^^^^^^ [2]