Force JSON to no trailing comma in multiparser (#3182)

* Force JSON to no trailing comma in multiparser

* Switch to mutate next.options

src/multiparser.js

@@ -14,6 +14,9 @@ function printSubtree(subtreeParser, path, print, options) {
   next.options = Object.assign({}, options, next.options, {
     originalText: next.text
   });
+  if (next.options.parser === "json") {
+    next.options.trailingComma = "none";
+  }
   const ast = require("./parser").parse(next.text, next.options);
   const astComments = ast.comments;
   delete ast.comments;

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

@@ -0,0 +1,16 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`trailing_comma.md 1`] = `
+\`\`\`json
+{
+  "foo": "bar"
+}
+\`\`\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\`\`\`json
+{
+  "foo": "bar"
+}
+\`\`\`
+
+`;

tests/multiparser_markdown_json/jsfmt.spec.js

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

tests/multiparser_markdown_json/trailing_comma.md

@@ -0,0 +1,5 @@
+```json
+{
+  "foo": "bar"
+}
+```