Keep comments of default cases in the same line of the case (#12177)

changelog_unreleased/javascript/12177.md

@@ -0,0 +1,40 @@
+#### Keep comments after `default` cases in the same line (#12177 by @duailibe)
+
+Keep comments right after `default` cases (in switch statements) in the same line, when possible.
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+function read_statement() {
+  switch (peek_keyword()) {
+    case Keyword.impl: // impl<T> Growling<T> for Wolf {}
+      return ImplDeclaration.read();
+
+    default: // expression;
+      return ExpressionStatement.read();
+  }
+}
+
+// Prettier stable
+function read_statement() {
+  switch (peek_keyword()) {
+    case Keyword.impl: // impl<T> Growling<T> for Wolf {}
+      return ImplDeclaration.read();
+
+    default:
+      // expression;
+      return ExpressionStatement.read();
+  }
+}
+
+// Prettier main
+function read_statement() {
+  switch (peek_keyword()) {
+    case Keyword.impl: // impl<T> Growling<T> for Wolf {}
+      return ImplDeclaration.read();
+
+    default: // expression;
+      return ExpressionStatement.read();
+  }
+}
+```

src/language-js/comments.js

@@ -24,6 +24,7 @@ const {
   isCallExpression,
   isMemberExpression,
   isObjectProperty,
+  isLineComment,
   getComments,
   CommentCheckFlags,
   markerForIfWithoutBlockAndSameLineComment,
@@ -93,6 +94,7 @@ function handleEndOfLineComment(context) {
     handleTypeAliasComments,
     handleVariableDeclaratorComments,
     handleBreakAndContinueStatementComments,
+    handleSwitchDefaultCaseComments,
   ].some((fn) => fn(context));
 }
 
@@ -897,6 +899,28 @@ function handleTSMappedTypeComments({
   return false;
 }
 
+function handleSwitchDefaultCaseComments({
+  comment,
+  enclosingNode,
+  followingNode,
+}) {
+  if (
+    !enclosingNode ||
+    enclosingNode.type !== "SwitchCase" ||
+    enclosingNode.test
+  ) {
+    return false;
+  }
+
+  if (followingNode.type === "BlockStatement" && isLineComment(comment)) {
+    addBlockStatementFirstComment(followingNode, comment);
+  } else {
+    addDanglingComment(enclosingNode, comment);
+  }
+
+  return true;
+}
+
 /**
  * @param {Node} node
  * @returns {boolean}

src/language-js/printer-estree.js

@@ -696,6 +696,10 @@ function printPathNoParens(path, options, print, args) {
         parts.push("default:");
       }
 
+      if (hasComment(node, CommentCheckFlags.Dangling)) {
+        parts.push(" ", printDanglingComments(path, options, true));
+      }
+
       const consequent = node.consequent.filter(
         (node) => node.type !== "EmptyStatement"
       );

tests/format/js/switch/__snapshots__/jsfmt.spec.js.snap

@@ -30,6 +30,41 @@ switch(x) {
   }
 }
 
+switch(x) {
+  default: // comment
+    break;
+}
+
+switch(x) {
+  default: // comment
+    {break;}
+}
+
+switch(x) {
+  default: {// comment
+    break;}
+}
+
+switch(x) {
+  default: /* comment */
+    break;
+}
+
+switch(x) {
+  default: /* comment */
+    {break;}
+}
+
+switch(x) {
+  default: {/* comment */
+    break;}
+}
+
+switch(x) {
+  default: /* comment */ {
+    break;}
+}
+
 =====================================output=====================================
 switch (true) {
   case true:
@@ -55,6 +90,49 @@ switch (x) {
   }
 }
 
+switch (x) {
+  default: // comment
+    break;
+}
+
+switch (x) {
+  default: {
+    // comment
+    break;
+  }
+}
+
+switch (x) {
+  default: {
+    // comment
+    break;
+  }
+}
+
+switch (x) {
+  default: /* comment */
+    break;
+}
+
+switch (x) {
+  default: /* comment */ {
+    break;
+  }
+}
+
+switch (x) {
+  default: {
+    /* comment */
+    break;
+  }
+}
+
+switch (x) {
+  default: /* comment */ {
+    break;
+  }
+}
+
 ================================================================================
 `;
 

tests/format/js/switch/comments.js

@@ -21,3 +21,38 @@ switch(x) {
   case y: {
   }
 }
+
+switch(x) {
+  default: // comment
+    break;
+}
+
+switch(x) {
+  default: // comment
+    {break;}
+}
+
+switch(x) {
+  default: {// comment
+    break;}
+}
+
+switch(x) {
+  default: /* comment */
+    break;
+}
+
+switch(x) {
+  default: /* comment */
+    {break;}
+}
+
+switch(x) {
+  default: {/* comment */
+    break;}
+}
+
+switch(x) {
+  default: /* comment */ {
+    break;}
+}