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Diffstat (limited to 'tools/node_modules/eslint/lib/rules/no-useless-return.js')
| -rw-r--r-- | tools/node_modules/eslint/lib/rules/no-useless-return.js | 304 |
1 files changed, 304 insertions, 0 deletions
diff --git a/tools/node_modules/eslint/lib/rules/no-useless-return.js b/tools/node_modules/eslint/lib/rules/no-useless-return.js new file mode 100644 index 0000000000..5415bf59b8 --- /dev/null +++ b/tools/node_modules/eslint/lib/rules/no-useless-return.js @@ -0,0 +1,304 @@ +/** + * @fileoverview Disallow redundant return statements + * @author Teddy Katz + */ +"use strict"; + +//------------------------------------------------------------------------------ +// Requirements +//------------------------------------------------------------------------------ + +const astUtils = require("../ast-utils"), + FixTracker = require("../util/fix-tracker"); + +//------------------------------------------------------------------------------ +// Helpers +//------------------------------------------------------------------------------ + +/** + * Adds all elements of 2nd argument into 1st argument. + * + * @param {Array} array - The destination array to add. + * @param {Array} elements - The source array to add. + * @returns {void} + */ +const pushAll = Function.apply.bind(Array.prototype.push); + +/** + * 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) { + while (node && node.parent && !astUtils.isFunction(node)) { + if (node.parent.type === "TryStatement" && node.parent.finalizer === node) { + return true; + } + + node = node.parent; + } + + return false; +} + +//------------------------------------------------------------------------------ +// Rule Definition +//------------------------------------------------------------------------------ + +module.exports = { + meta: { + docs: { + description: "disallow redundant return statements", + category: "Best Practices", + recommended: false + }, + fixable: "code", + schema: [] + }, + + create(context) { + const segmentInfoMap = new WeakMap(); + const usedUnreachableSegments = new WeakSet(); + 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>} [traversedSegments] A set of segments that have already been traversed in this call + * @returns {ASTNode[]} `uselessReturns`. + */ + function getUselessReturns(uselessReturns, prevSegments, traversedSegments) { + if (!traversedSegments) { + traversedSegments = 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; + } + + pushAll(uselessReturns, 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)) { + + /* + * 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, context.getSourceCode()) + .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)) { + 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 + }; + } +}; |