d2-ui
Version:
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JavaScript
/**
* @fileoverview Rule to flag `else` after a `return` in `if`
* @author Ian Christian Myers
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "disallow `else` blocks after `return` statements in `if` statements",
category: "Best Practices",
recommended: false
},
schema: []
},
create: function(context) {
//--------------------------------------------------------------------------
// Helpers
//--------------------------------------------------------------------------
/**
* Display the context report if rule is violated
*
* @param {Node} node The 'else' node
* @returns {void}
*/
function displayReport(node) {
context.report(node, "Unexpected 'else' after 'return'.");
}
/**
* Check to see if the node is a ReturnStatement
*
* @param {Node} node The node being evaluated
* @returns {boolean} True if node is a return
*/
function checkForReturn(node) {
return node.type === "ReturnStatement";
}
/**
* Naive return checking, does not iterate through the whole
* BlockStatement because we make the assumption that the ReturnStatement
* will be the last node in the body of the BlockStatement.
*
* @param {Node} node The consequent/alternate node
* @returns {boolean} True if it has a return
*/
function naiveHasReturn(node) {
if (node.type === "BlockStatement") {
var body = node.body,
lastChildNode = body[body.length - 1];
return lastChildNode && checkForReturn(lastChildNode);
}
return checkForReturn(node);
}
/**
* Check to see if the node is valid for evaluation,
* meaning it has an else and not an else-if
*
* @param {Node} node The node being evaluated
* @returns {boolean} True if the node is valid
*/
function hasElse(node) {
return node.alternate && node.consequent && node.alternate.type !== "IfStatement";
}
/**
* If the consequent is an IfStatement, check to see if it has an else
* and both its consequent and alternate path return, meaning this is
* a nested case of rule violation. If-Else not considered currently.
*
* @param {Node} node The consequent node
* @returns {boolean} True if this is a nested rule violation
*/
function checkForIf(node) {
return node.type === "IfStatement" && hasElse(node) &&
naiveHasReturn(node.alternate) && naiveHasReturn(node.consequent);
}
/**
* Check the consequent/body node to make sure it is not
* a ReturnStatement or an IfStatement that returns on both
* code paths.
*
* @param {Node} node The consequent or body node
* @param {Node} alternate The alternate node
* @returns {boolean} `true` if it is a Return/If node that always returns.
*/
function checkForReturnOrIf(node) {
return checkForReturn(node) || checkForIf(node);
}
/**
* Check whether a node returns in every codepath.
* @param {Node} node The node to be checked
* @returns {boolean} `true` if it returns on every codepath.
*/
function alwaysReturns(node) {
if (node.type === "BlockStatement") {
// If we have a BlockStatement, check each consequent body node.
return node.body.some(checkForReturnOrIf);
} else {
/*
* If not a block statement, make sure the consequent isn't a
* ReturnStatement or an IfStatement with returns on both paths.
*/
return checkForReturnOrIf(node);
}
}
//--------------------------------------------------------------------------
// Public API
//--------------------------------------------------------------------------
return {
IfStatement: function(node) {
var parent = context.getAncestors().pop(),
consequents,
alternate;
// Only "top-level" if statements are checked, meaning the first `if`
// in a `if-else-if-...` chain.
if (parent.type === "IfStatement" && parent.alternate === node) {
return;
}
for (consequents = []; node.type === "IfStatement"; node = node.alternate) {
if (!node.alternate) {
return;
}
consequents.push(node.consequent);
alternate = node.alternate;
}
if (consequents.every(alwaysReturns)) {
displayReport(alternate);
}
}
};
}
};