Internal slot properties (#7947)

* Support internalSlots to babel-types and babel-generator

* Parsing support for internal slot properties

* Print internal slots in babel-generator

* Add whitespace before first internal slot property

packages/babel-generator/test/fixtures/flow/internal-slot/input.js

@@ -0,0 +1,6 @@
+declare class C { static [[foo]]: T }
+declare class C { [[foo]]: T }
+interface T { [[foo]]: X }
+interface T { [[foo]](): X }
+type T = { [[foo]]: X }
+type T = { [[foo]](): X }

packages/babel-generator/test/fixtures/flow/internal-slot/output.js

@@ -0,0 +1,18 @@
+declare class C {
+  static [[foo]]: T
+}
+declare class C {
+  [[foo]]: T
+}
+interface T {
+  [[foo]]: X
+}
+interface T {
+  [[foo]]() => X
+}
+type T = {
+  [[foo]]: X
+};
+type T = {
+  [[foo]]() => X
+};

packages/babel-generator/test/index.js

@@ -304,6 +304,7 @@ describe("programmatic generation", function() {
       [t.objectTypeProperty(t.identifier("bar"), t.stringTypeAnnotation())],
       null,
       null,
+      null,
     );
 
     const output = generate(objectStatement).code;
@@ -317,6 +318,7 @@ describe("programmatic generation", function() {
       [t.objectTypeProperty(t.identifier("bar"), t.stringTypeAnnotation())],
       null,
       null,
+      null,
       true,
     );
 
@@ -336,6 +338,7 @@ describe("programmatic generation", function() {
           t.numberTypeAnnotation(),
         ),
       ],
+      null,
     );
 
     const output = generate(objectStatement).code;