+++ /dev/null
-/**
- * @fileoverview Disallow redundant return statements
- * @author Teddy Katz
- */
-"use strict";
-
-//------------------------------------------------------------------------------
-// Requirements
-//------------------------------------------------------------------------------
-
-const astUtils = require("./utils/ast-utils"),
- FixTracker = require("./utils/fix-tracker");
-
-//------------------------------------------------------------------------------
-// Helpers
-//------------------------------------------------------------------------------
-
-/**
- * Removes the given element from the array.
- * @param {Array} array The source array to remove.
- * @param {any} element The target item to remove.
- * @returns {void}
- */
-function remove(array, element) {
- const index = array.indexOf(element);
-
- if (index !== -1) {
- array.splice(index, 1);
- }
-}
-
-/**
- * Checks whether it can remove the given return statement or not.
- * @param {ASTNode} node The return statement node to check.
- * @returns {boolean} `true` if the node is removeable.
- */
-function isRemovable(node) {
- return astUtils.STATEMENT_LIST_PARENTS.has(node.parent.type);
-}
-
-/**
- * Checks whether the given return statement is in a `finally` block or not.
- * @param {ASTNode} node The return statement node to check.
- * @returns {boolean} `true` if the node is in a `finally` block.
- */
-function isInFinally(node) {
- for (
- let currentNode = node;
- currentNode && currentNode.parent && !astUtils.isFunction(currentNode);
- currentNode = currentNode.parent
- ) {
- if (currentNode.parent.type === "TryStatement" && currentNode.parent.finalizer === currentNode) {
- return true;
- }
- }
-
- return false;
-}
-
-//------------------------------------------------------------------------------
-// Rule Definition
-//------------------------------------------------------------------------------
-
-module.exports = {
- meta: {
- type: "suggestion",
-
- docs: {
- description: "disallow redundant return statements",
- category: "Best Practices",
- recommended: false,
- url: "https://eslint.org/docs/rules/no-useless-return"
- },
-
- fixable: "code",
- schema: []
- },
-
- create(context) {
- const segmentInfoMap = new WeakMap();
- const usedUnreachableSegments = new WeakSet();
- const sourceCode = context.getSourceCode();
- let scopeInfo = null;
-
- /**
- * Checks whether the given segment is terminated by a return statement or not.
- * @param {CodePathSegment} segment The segment to check.
- * @returns {boolean} `true` if the segment is terminated by a return statement, or if it's still a part of unreachable.
- */
- function isReturned(segment) {
- const info = segmentInfoMap.get(segment);
-
- return !info || info.returned;
- }
-
- /**
- * Collects useless return statements from the given previous segments.
- *
- * A previous segment may be an unreachable segment.
- * In that case, the information object of the unreachable segment is not
- * initialized because `onCodePathSegmentStart` event is not notified for
- * unreachable segments.
- * This goes to the previous segments of the unreachable segment recursively
- * if the unreachable segment was generated by a return statement. Otherwise,
- * this ignores the unreachable segment.
- *
- * This behavior would simulate code paths for the case that the return
- * statement does not exist.
- * @param {ASTNode[]} uselessReturns The collected return statements.
- * @param {CodePathSegment[]} prevSegments The previous segments to traverse.
- * @param {WeakSet<CodePathSegment>} [providedTraversedSegments] A set of segments that have already been traversed in this call
- * @returns {ASTNode[]} `uselessReturns`.
- */
- function getUselessReturns(uselessReturns, prevSegments, providedTraversedSegments) {
- const traversedSegments = providedTraversedSegments || new WeakSet();
-
- for (const segment of prevSegments) {
- if (!segment.reachable) {
- if (!traversedSegments.has(segment)) {
- traversedSegments.add(segment);
- getUselessReturns(
- uselessReturns,
- segment.allPrevSegments.filter(isReturned),
- traversedSegments
- );
- }
- continue;
- }
-
- uselessReturns.push(...segmentInfoMap.get(segment).uselessReturns);
- }
-
- return uselessReturns;
- }
-
- /**
- * Removes the return statements on the given segment from the useless return
- * statement list.
- *
- * This segment may be an unreachable segment.
- * In that case, the information object of the unreachable segment is not
- * initialized because `onCodePathSegmentStart` event is not notified for
- * unreachable segments.
- * This goes to the previous segments of the unreachable segment recursively
- * if the unreachable segment was generated by a return statement. Otherwise,
- * this ignores the unreachable segment.
- *
- * This behavior would simulate code paths for the case that the return
- * statement does not exist.
- * @param {CodePathSegment} segment The segment to get return statements.
- * @returns {void}
- */
- function markReturnStatementsOnSegmentAsUsed(segment) {
- if (!segment.reachable) {
- usedUnreachableSegments.add(segment);
- segment.allPrevSegments
- .filter(isReturned)
- .filter(prevSegment => !usedUnreachableSegments.has(prevSegment))
- .forEach(markReturnStatementsOnSegmentAsUsed);
- return;
- }
-
- const info = segmentInfoMap.get(segment);
-
- for (const node of info.uselessReturns) {
- remove(scopeInfo.uselessReturns, node);
- }
- info.uselessReturns = [];
- }
-
- /**
- * Removes the return statements on the current segments from the useless
- * return statement list.
- *
- * This function will be called at every statement except FunctionDeclaration,
- * BlockStatement, and BreakStatement.
- *
- * - FunctionDeclarations are always executed whether it's returned or not.
- * - BlockStatements do nothing.
- * - BreakStatements go the next merely.
- * @returns {void}
- */
- function markReturnStatementsOnCurrentSegmentsAsUsed() {
- scopeInfo
- .codePath
- .currentSegments
- .forEach(markReturnStatementsOnSegmentAsUsed);
- }
-
- //----------------------------------------------------------------------
- // Public
- //----------------------------------------------------------------------
-
- return {
-
- // Makes and pushs a new scope information.
- onCodePathStart(codePath) {
- scopeInfo = {
- upper: scopeInfo,
- uselessReturns: [],
- codePath
- };
- },
-
- // Reports useless return statements if exist.
- onCodePathEnd() {
- for (const node of scopeInfo.uselessReturns) {
- context.report({
- node,
- loc: node.loc,
- message: "Unnecessary return statement.",
- fix(fixer) {
- if (isRemovable(node) && !sourceCode.getCommentsInside(node).length) {
-
- /*
- * Extend the replacement range to include the
- * entire function to avoid conflicting with
- * no-else-return.
- * https://github.com/eslint/eslint/issues/8026
- */
- return new FixTracker(fixer, sourceCode)
- .retainEnclosingFunction(node)
- .remove(node);
- }
- return null;
- }
- });
- }
-
- scopeInfo = scopeInfo.upper;
- },
-
- /*
- * Initializes segments.
- * NOTE: This event is notified for only reachable segments.
- */
- onCodePathSegmentStart(segment) {
- const info = {
- uselessReturns: getUselessReturns([], segment.allPrevSegments),
- returned: false
- };
-
- // Stores the info.
- segmentInfoMap.set(segment, info);
- },
-
- // Adds ReturnStatement node to check whether it's useless or not.
- ReturnStatement(node) {
- if (node.argument) {
- markReturnStatementsOnCurrentSegmentsAsUsed();
- }
- if (
- node.argument ||
- astUtils.isInLoop(node) ||
- isInFinally(node) ||
-
- // Ignore `return` statements in unreachable places (https://github.com/eslint/eslint/issues/11647).
- !scopeInfo.codePath.currentSegments.some(s => s.reachable)
- ) {
- return;
- }
-
- for (const segment of scopeInfo.codePath.currentSegments) {
- const info = segmentInfoMap.get(segment);
-
- if (info) {
- info.uselessReturns.push(node);
- info.returned = true;
- }
- }
- scopeInfo.uselessReturns.push(node);
- },
-
- /*
- * Registers for all statement nodes except FunctionDeclaration, BlockStatement, BreakStatement.
- * Removes return statements of the current segments from the useless return statement list.
- */
- ClassDeclaration: markReturnStatementsOnCurrentSegmentsAsUsed,
- ContinueStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- DebuggerStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- DoWhileStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- EmptyStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ExpressionStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ForInStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ForOfStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ForStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- IfStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ImportDeclaration: markReturnStatementsOnCurrentSegmentsAsUsed,
- LabeledStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- SwitchStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ThrowStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- TryStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- VariableDeclaration: markReturnStatementsOnCurrentSegmentsAsUsed,
- WhileStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- WithStatement: markReturnStatementsOnCurrentSegmentsAsUsed,
- ExportNamedDeclaration: markReturnStatementsOnCurrentSegmentsAsUsed,
- ExportDefaultDeclaration: markReturnStatementsOnCurrentSegmentsAsUsed,
- ExportAllDeclaration: markReturnStatementsOnCurrentSegmentsAsUsed
- };
- }
-};
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