[generator] remove parens from break & continue (#5950)

* Remove parens around break and continue

Fixes #5742

* Fix space in doc comment

* Add some tests

* Remove newlines within CommentBlock

* Prevent newline before/after label

* Remove reference to node

* Check for label within startTerminatorless

* Print block instead of single line comment

* Clean up

packages/babel-generator/src/generators/statements.js

@@ -123,8 +123,8 @@ function buildLabelStatement(prefix, key = "label") {
     const label = node[key];
     if (label) {
       this.space();
-
-      const terminatorState = this.startTerminatorless();
+      const isLabel = key == "label";
+      const terminatorState = this.startTerminatorless(isLabel);
       this.print(label, node);
       this.endTerminatorless(terminatorState);
     }

packages/babel-generator/src/printer.js

@@ -43,6 +43,7 @@ export default class Printer {
   _insideAux: boolean = false;
   _printedCommentStarts: Object = {};
   _parenPushNewlineState: ?Object = null;
+  _noLineTerminator: boolean = false;
   _printAuxAfterOnNextUserNode: boolean = false;
   _printedComments: WeakSet = new WeakSet();
   _endsWithInteger = false;
@@ -281,7 +282,7 @@ export default class Printer {
    *
    * This is to prevent breaking semantics for terminatorless separator nodes. eg:
    *
-   *    return foo;
+   *   return foo;
    *
    * returns `foo`. But if we do:
    *
@@ -291,10 +292,15 @@ export default class Printer {
    *  `undefined` will be returned and not `foo` due to the terminator.
    */
 
-  startTerminatorless(): Object {
-    return (this._parenPushNewlineState = {
-      printed: false,
-    });
+  startTerminatorless(isLabel: boolean = false): Object {
+    if (isLabel) {
+      this._noLineTerminator = true;
+      return null;
+    } else {
+      return (this._parenPushNewlineState = {
+        printed: false,
+      });
+    }
   }
 
   /**
@@ -302,7 +308,8 @@ export default class Printer {
    */
 
   endTerminatorless(state: Object) {
-    if (state.printed) {
+    this._noLineTerminator = false;
+    if (state && state.printed) {
       this.dedent();
       this.newline();
       this.token(")");
@@ -530,13 +537,19 @@ export default class Printer {
     const isBlockComment = comment.type === "CommentBlock";
 
     // Always add a newline before a block comment
-    this.newline(this._buf.hasContent() && isBlockComment ? 1 : 0);
+    this.newline(
+      this._buf.hasContent() && !this._noLineTerminator && isBlockComment
+        ? 1
+        : 0,
+    );
 
     if (!this.endsWith("[") && !this.endsWith("{")) this.space();
 
-    let val = !isBlockComment ? `//${comment.value}\n` : `/*${comment.value}*/`;
+    let val =
+      !isBlockComment && !this._noLineTerminator
+        ? `//${comment.value}\n`
+        : `/*${comment.value}*/`;
 
-    //
     if (isBlockComment && this.format.indent.adjustMultilineComment) {
       const offset = comment.loc && comment.loc.start.column;
       if (offset) {
@@ -559,7 +572,7 @@ export default class Printer {
     });
 
     // Always add a newline after a block comment
-    this.newline(isBlockComment ? 1 : 0);
+    this.newline(isBlockComment && !this._noLineTerminator ? 1 : 0);
   }
 
   _printComments(comments?: Array<Object>) {

packages/babel-generator/test/fixtures/parentheses/break-statement/actual.js

@@ -0,0 +1,13 @@
+label1: for (const a of [1, 2, 3]) {
+  break /*Block comment written in single line */ label1;
+}
+
+label2: for (const a of [1, 2, 3]) {
+  break /*Block comment written
+  in multiple lines */ label2;
+}
+
+label2: for (const a of [1, 2, 3]) {
+  break //foo
+    label2;
+}

packages/babel-generator/test/fixtures/parentheses/break-statement/expected.js

@@ -0,0 +1,17 @@
+label1: for (const a of [1, 2, 3]) {
+  break /*Block comment written in single line */label1;
+}
+
+label2: for (const a of [1, 2, 3]) {
+  break;
+  /*Block comment written
+  in multiple lines */
+
+  label2;
+}
+
+label2: for (const a of [1, 2, 3]) {
+  break; //foo
+
+  label2;
+}