[PR] Fix for class method default parameters that use this

Summary:
Example of bug - https://flowtype.org/try/#0PQKgBAAgZgNg9gdzCYAoVBjGBDAzrsAQTAG9UwxyxsAuMXAFwCcBLAOwHMqqAjACgxgAvGAYALFrgB02AJSkqFKgF9uyoA

Fixes #3353
Fixes #1234

Closes #3334

Reviewed By: samwgoldman

Differential Revision: D4523083

Pulled By: jeffmo

fbshipit-source-id: 6e8be65711263182d8eef568ae34a46d77b399a3

src/typing/func_sig.ml

@@ -233,6 +233,13 @@ let toplevels id cx this super ~decls ~stmts ~expr
   (* push the scope early so default exprs can reference earlier params *)
   Env.push_var_scope cx function_scope;
 
+  (* add `this` and `super` before looking at parameter bindings as when using
+   * `this` in default parameter values it refers to the function scope and
+   * `super` should resolve to the method's [[HomeObject]]
+  *)
+  Scope.add_entry (internal_name "this") this function_scope;
+  Scope.add_entry (internal_name "super") super function_scope;
+
   (* bind type params *)
   SMap.iter (fun name t ->
     let r = reason_of_t t in
@@ -290,8 +297,6 @@ let toplevels id cx this super ~decls ~stmts ~expr
     new_entry yield_t, new_entry next_t, new_entry return_t
   ) in
 
-  Scope.add_entry (internal_name "this") this function_scope;
-  Scope.add_entry (internal_name "super") super function_scope;
   Scope.add_entry (internal_name "yield") yield function_scope;
   Scope.add_entry (internal_name "next") next function_scope;
   Scope.add_entry (internal_name "return") return function_scope;

tests/class_method_default_parameters/.flowconfig

@@ -0,0 +1,2 @@
+[options]
+no_flowlib=false

tests/class_method_default_parameters/class_method_default_parameters.exp

@@ -0,0 +1,8 @@
+class_method_default_parameters.js:17
+ 17:     h(i: number = this.b) { // error
+                       ^^^^^^ string. This type is incompatible with
+ 17:     h(i: number = this.b) { // error
+              ^^^^^^ number
+
+
+Found 1 error

tests/class_method_default_parameters/class_method_default_parameters.js

@@ -0,0 +1,21 @@
+class A {
+
+    b: string;
+
+    c(d = this.b) { // ok - can use `this` in function default parameter values
+
+    }
+
+    e() {
+        return this.b;
+    }
+
+    f(g = this.e()) { // ok - can use `this` in function default parameter values
+
+    }
+
+    h(i: number = this.b) { // error
+
+    }
+
+}