Do not prepend / append with a semicolon the only JSX element in a program (#3330)

* Do not prepend / append with a semicolon the only JSX element in a program

Fixes #3196

* Limit single JSX element without semicolon to Markdown only

* Fix tests

src/multiparser.js

@@ -12,6 +12,7 @@ const concat = docBuilders.concat;
 function printSubtree(subtreeParser, path, print, options) {
   const next = Object.assign({}, { transformDoc: doc => doc }, subtreeParser);
   next.options = Object.assign({}, options, next.options, {
+    parentParser: options.parser,
     originalText: next.text
   });
   if (next.options.parser === "json") {

src/printer.js

@@ -292,7 +292,11 @@ function genericPrintNoParens(path, options, print, args) {
       if (n.directive) {
         return concat([nodeStr(n.expression, options, true), semi]);
       }
-      return concat([path.call(print, "expression"), semi]); // Babel extension.
+      // Do not append semicolon after the only JSX element in a program
+      return concat([
+        path.call(print, "expression"),
+        isTheOnlyJSXElementInMarkdown(options, path) ? "" : semi
+      ]); // Babel extension.
     case "ParenthesizedExpression":
       return concat(["(", path.call(print, "expression"), ")"]);
     case "AssignmentExpression":
@@ -2864,7 +2868,13 @@ function printStatementSequence(path, options, print) {
     const parts = [];
 
     // in no-semi mode, prepend statement with semicolon if it might break ASI
-    if (!options.semi && !isClass && stmtNeedsASIProtection(stmtPath)) {
+    // don't prepend the only JSX element in a program with semicolon
+    if (
+      !options.semi &&
+      !isClass &&
+      !isTheOnlyJSXElementInMarkdown(options, stmtPath) &&
+      stmtNeedsASIProtection(stmtPath)
+    ) {
       if (stmt.comments && stmt.comments.some(comment => comment.leading)) {
         // Note: stmtNeedsASIProtection requires stmtPath to already be printed
         // as it reads needsParens which is mutated on the instance
@@ -5047,4 +5057,20 @@ function printAstToDoc(ast, options, addAlignmentSize) {
   return doc;
 }
 
+function isTheOnlyJSXElementInMarkdown(options, path) {
+  if (options.parentParser !== "markdown") {
+    return false;
+  }
+
+  const node = path.getNode();
+
+  if (!node.expression || node.expression.type !== "JSXElement") {
+    return false;
+  }
+
+  const parent = path.getParentNode();
+
+  return parent.type === "Program" && parent.body.length == 1;
+}
+
 module.exports = { printAstToDoc };

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

@@ -0,0 +1,43 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`semi.md 1`] = `
+\`\`\`jsx
+<div>foo</div>
+\`\`\`
+
+\`\`\`jsx
+const a = 1;
+<div>foo</div>;
+\`\`\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\`\`\`jsx
+<div>foo</div>
+\`\`\`
+
+\`\`\`jsx
+const a = 1;
+<div>foo</div>;
+\`\`\`
+
+`;
+
+exports[`semi.md 2`] = `
+\`\`\`jsx
+<div>foo</div>
+\`\`\`
+
+\`\`\`jsx
+const a = 1;
+<div>foo</div>;
+\`\`\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\`\`\`jsx
+<div>foo</div>
+\`\`\`
+
+\`\`\`jsx
+const a = 1
+;<div>foo</div>
+\`\`\`
+
+`;

tests/markdown_jsx_semi/jsfmt.spec.js

@@ -0,0 +1,2 @@
+run_spec(__dirname, { semi: true, parser: "markdown" });
+run_spec(__dirname, { semi: false, parser: "markdown" });

tests/markdown_jsx_semi/semi.md

@@ -0,0 +1,8 @@
+```jsx
+<div>foo</div>
+```
+
+```jsx
+const a = 1;
+<div>foo</div>;
+```