Allow formatting ranges of JSON (#2298)

* Add test for https://github.com/prettier/prettier/issues/2297

* Add JSON types to isSourceElement()

See https://github.com/prettier/prettier/issues/2297

* Avoid expanding format range when possible

This fixes https://github.com/prettier/prettier/issues/2297

* Move JSON range test into tests/range_json

This is so that the AST_COMPARE=1 tests don't try to parse JSON with Flow.

* Check parser in isSourceElement()

Otherwise JSON formatting would format weird things inside of JS.
See https://github.com/prettier/prettier/pull/2298#discussion_r124407056

* Use arrow functions instead of .bind()

See https://github.com/prettier/prettier/pull/2298#discussion_r124409783

* Add test of range-formatting JSON identifier

See https://github.com/prettier/prettier/pull/2298/files#r124410750

* Allow range-formatting JSON identifier

See https://github.com/prettier/prettier/pull/2298/files#r124410750

* Fix lint

index.js

@@ -103,6 +103,13 @@ function findSiblingAncestors(startNodeAndParents, endNodeAndParents) {
   let resultStartNode = startNodeAndParents.node;
   let resultEndNode = endNodeAndParents.node;
 
+  if (resultStartNode === resultEndNode) {
+    return {
+      startNode: resultStartNode,
+      endNode: resultEndNode
+    };
+  }
+
   for (const endParent of endNodeAndParents.parentNodes) {
     if (
       endParent.type !== "Program" &&
@@ -161,11 +168,19 @@ function findNodeAtOffset(node, offset, predicate, parentNodes) {
 }
 
 // See https://www.ecma-international.org/ecma-262/5.1/#sec-A.5
-function isSourceElement(node) {
+function isSourceElement(opts, node) {
   if (node == null) {
     return false;
   }
   switch (node.type) {
+    case "ObjectExpression": // JSON
+    case "ArrayExpression": // JSON
+    case "StringLiteral": // JSON
+    case "NumericLiteral": // JSON
+    case "BooleanLiteral": // JSON
+    case "NullLiteral": // JSON
+    case "json-identifier": // JSON
+      return opts.parser === "json";
     case "FunctionDeclaration":
     case "BlockStatement":
     case "BreakStatement":
@@ -219,15 +234,11 @@ function calculateRange(text, opts, ast) {
     }
   }
 
-  const startNodeAndParents = findNodeAtOffset(
-    ast,
-    startNonWhitespace,
-    isSourceElement
+  const startNodeAndParents = findNodeAtOffset(ast, startNonWhitespace, node =>
+    isSourceElement(opts, node)
   );
-  const endNodeAndParents = findNodeAtOffset(
-    ast,
-    endNonWhitespace,
-    isSourceElement
+  const endNodeAndParents = findNodeAtOffset(ast, endNonWhitespace, node =>
+    isSourceElement(opts, node)
   );
 
   if (!startNodeAndParents || !endNodeAndParents) {

tests/range_json/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,15 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`identifier.json 1`] = `
+{"a":1, "b":2}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+{"a":1, "b":2}
+
+`;
+
+exports[`issue2297.json 1`] = `
+{"a":1, "b":2}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+{"a":1, "b":2}
+
+`;

tests/range_json/identifier.json

@@ -0,0 +1 @@
+{<<<PRETTIER_RANGE_START>>>"a"<<<PRETTIER_RANGE_END>>>:1, "b":2}

tests/range_json/issue2297.json

@@ -0,0 +1 @@
+{"a":<<<PRETTIER_RANGE_START>>>1<<<PRETTIER_RANGE_END>>>, "b":2}

tests/range_json/jsfmt.spec.js

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