feat: add allowEmptyCase option to no-fallthrough rule

lib/rules/no-fallthrough.js

@@ -35,6 +35,19 @@ function hasFallthroughComment(caseWhichFallsThrough, subsequentCase, context, f
     return Boolean(comment && fallthroughCommentPattern.test(comment.value));
 }
 
+/**
+ * Checks whether or not a given case is empty.
+ * @param {ASTNode} caseWhichFallsThrough SwitchCase node which falls through.
+ * @returns {boolean} `true` if the case is empty.
+ */
+function isEmptyCase(caseWhichFallsThrough) {
+    if (caseWhichFallsThrough.consequent.length === 0 ||
+        (caseWhichFallsThrough.consequent.length === 1 && caseWhichFallsThrough.consequent[0].type === "EmptyStatement")) {
+        return true;
+    }
+    return false;
+}
+
 /**
  * Checks whether or not a given code path segment is reachable.
  * @param {CodePathSegment} segment A CodePathSegment to check.
@@ -76,6 +89,10 @@ module.exports = {
                     commentPattern: {
                         type: "string",
                         default: ""
+                    },
+                    allowEmptyCase: {
+                        type: "boolean",
+                        default: false
                     }
                 },
                 additionalProperties: false
@@ -91,6 +108,7 @@ module.exports = {
         const options = context.options[0] || {};
         let currentCodePath = null;
         const sourceCode = context.getSourceCode();
+        const allowEmptyCase = options.allowEmptyCase || false;
 
         /*
          * We need to use leading comments of the next SwitchCase node because
@@ -104,7 +122,6 @@ module.exports = {
         } else {
             fallthroughCommentPattern = DEFAULT_FALLTHROUGH_COMMENT;
         }
-
         return {
             onCodePathStart(codePath) {
                 currentCodePath = codePath;
@@ -118,19 +135,25 @@ module.exports = {
                 /*
                  * Checks whether or not there is a fallthrough comment.
                  * And reports the previous fallthrough node if that does not exist.
+                 *
+                 *
                  */
-                if (fallthroughCase && !hasFallthroughComment(fallthroughCase, node, context, fallthroughCommentPattern)) {
-                    context.report({
-                        messageId: node.test ? "case" : "default",
-                        node
-                    });
+
+                if (fallthroughCase && (!hasFallthroughComment(fallthroughCase, node, context, fallthroughCommentPattern))) {
+                    if (!(allowEmptyCase && isEmptyCase(fallthroughCase))) {
+                        context.report({
+                            messageId: node.test ? "case" : "default",
+                            node
+                        });
+                    }
                 }
                 fallthroughCase = null;
             },
 
             "SwitchCase:exit"(node) {
                 const nextToken = sourceCode.getTokenAfter(node);
 
+
                 /*
                  * `reachable` meant fall through because statements preceded by
                  * `break`, `return`, or `throw` are unreachable.

tests/lib/rules/no-fallthrough.js

@@ -92,6 +92,14 @@ ruleTester.run("no-fallthrough", rule, {
             options: [{
                 commentPattern: "break[\\s\\w]+omitted"
             }]
+        },
+        {
+            code: "switch(foo) { case 0: \n\n\n case 1: b(); }",
+            options: [{ allowEmptyCase: true }]
+        },
+        {
+            code: "switch(foo) { case 0: \n /* with comments */  \n case 1: b(); }",
+            options: [{ allowEmptyCase: true }]
         }
     ],
     invalid: [
@@ -214,6 +222,17 @@ ruleTester.run("no-fallthrough", rule, {
                     column: 1
                 }
             ]
+        },
+        {
+            code: "switch(foo) { case 0: \n /* with comments */  \ncase 1: b(); }",
+            errors: [
+                {
+                    messageId: "case",
+                    type: "SwitchCase",
+                    line: 3,
+                    column: 1
+                }
+            ]
         }
     ]
 });