Fix empty file error in json and graphql (#4553)

* Fix empty file error in json and graphql

* fix AST_COMPARE=1 issue

* use tests/empty

* revert

* fix lint

src/language-js/printer-estree-json.js

@@ -49,6 +49,9 @@ function genericPrint(path, options, print) {
       return JSON.stringify(node.value);
     case "Identifier":
       return JSON.stringify(node.name);
+    default:
+      /* istanbul ignore next */
+      throw new Error("unknown type: " + JSON.stringify(node.type));
   }
 }
 

src/main/core.js

@@ -63,6 +63,10 @@ function attachComments(text, ast, opts) {
 }
 
 function coreFormat(text, opts, addAlignmentSize) {
+  if (!text || !text.trim().length) {
+    return { formatted: "", cursorOffset: 0 };
+  }
+
   addAlignmentSize = addAlignmentSize || 0;
 
   const parsed = parser.parse(text, opts);

tests/empty/jsfmt.spec.js

@@ -8,8 +8,4 @@ run_spec(
   parsers.choices
     .filter(choice => !choice.deprecated)
     .map(choice => choice.value)
-    .filter(
-      parser =>
-        ["json", "json5", "json-stringify", "graphql"].indexOf(parser) === -1
-    )
 );