add TSTypeOperator (#1396)

src/printer.js

@@ -1974,6 +1974,11 @@ function genericPrintNoParens(path, options, print, args) {
         ") => ",
         path.call(print, "typeAnnotation"),
       ])
+    case "TSTypeOperator":
+      return concat([
+        "keyof ",
+        path.call(print, "typeAnnotation")
+      ])
     // TODO
     case "ClassHeritage":
     // TODO

tests/typescript/conformance/types/typeOperator/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,8 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`typeOperator.ts 1`] = `
+let a: (keyof T)[] = ["a", "b"];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let a: (keyof T)[] = ["a", "b"];
+
+`;

tests/typescript/conformance/types/typeOperator/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, { parser: "typescript" });

tests/typescript/conformance/types/typeOperator/typeOperator.ts

@@ -0,0 +1 @@
+let a: (keyof T)[] = ["a", "b"];