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/**
* @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: []
},
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 message = node.parent.type === "BlockStatement" ? "Nested block is redundant." : "Block is redundant.";
context.report({ node, message });
}
/**
* Checks for any ocurrence 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;
}
};
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