--- /dev/null
+/**
+ * @fileoverview Rule to flag blocks with no reason to exist
+ * @author Brandon Mills
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "suggestion",
+
+ docs: {
+ description: "disallow unnecessary nested blocks",
+ category: "Best Practices",
+ recommended: false,
+ url: "https://eslint.org/docs/rules/no-lone-blocks"
+ },
+
+ schema: [],
+
+ messages: {
+ redundantBlock: "Block is redundant.",
+ redundantNestedBlock: "Nested block is redundant."
+ }
+ },
+
+ create(context) {
+
+ // A stack of lone blocks to be checked for block-level bindings
+ const loneBlocks = [];
+ let ruleDef;
+
+ /**
+ * Reports a node as invalid.
+ * @param {ASTNode} node The node to be reported.
+ * @returns {void}
+ */
+ function report(node) {
+ const messageId = node.parent.type === "BlockStatement" ? "redundantNestedBlock" : "redundantBlock";
+
+ context.report({
+ node,
+ messageId
+ });
+ }
+
+ /**
+ * Checks for any occurrence of a BlockStatement in a place where lists of statements can appear
+ * @param {ASTNode} node The node to check
+ * @returns {boolean} True if the node is a lone block.
+ */
+ function isLoneBlock(node) {
+ return node.parent.type === "BlockStatement" ||
+ node.parent.type === "Program" ||
+
+ // Don't report blocks in switch cases if the block is the only statement of the case.
+ node.parent.type === "SwitchCase" && !(node.parent.consequent[0] === node && node.parent.consequent.length === 1);
+ }
+
+ /**
+ * Checks the enclosing block of the current node for block-level bindings,
+ * and "marks it" as valid if any.
+ * @returns {void}
+ */
+ function markLoneBlock() {
+ if (loneBlocks.length === 0) {
+ return;
+ }
+
+ const block = context.getAncestors().pop();
+
+ if (loneBlocks[loneBlocks.length - 1] === block) {
+ loneBlocks.pop();
+ }
+ }
+
+ // Default rule definition: report all lone blocks
+ ruleDef = {
+ BlockStatement(node) {
+ if (isLoneBlock(node)) {
+ report(node);
+ }
+ }
+ };
+
+ // ES6: report blocks without block-level bindings, or that's only child of another block
+ if (context.parserOptions.ecmaVersion >= 6) {
+ ruleDef = {
+ BlockStatement(node) {
+ if (isLoneBlock(node)) {
+ loneBlocks.push(node);
+ }
+ },
+ "BlockStatement:exit"(node) {
+ if (loneBlocks.length > 0 && loneBlocks[loneBlocks.length - 1] === node) {
+ loneBlocks.pop();
+ report(node);
+ } else if (
+ node.parent.type === "BlockStatement" &&
+ node.parent.body.length === 1
+ ) {
+ report(node);
+ }
+ }
+ };
+
+ ruleDef.VariableDeclaration = function(node) {
+ if (node.kind === "let" || node.kind === "const") {
+ markLoneBlock();
+ }
+ };
+
+ ruleDef.FunctionDeclaration = function() {
+ if (context.getScope().isStrict) {
+ markLoneBlock();
+ }
+ };
+
+ ruleDef.ClassDeclaration = markLoneBlock;
+ }
+
+ return ruleDef;
+ }
+};