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Diffstat (limited to 'tools/node_modules/eslint/lib/rules/prefer-arrow-callback.js')
-rw-r--r-- | tools/node_modules/eslint/lib/rules/prefer-arrow-callback.js | 304 |
1 files changed, 304 insertions, 0 deletions
diff --git a/tools/node_modules/eslint/lib/rules/prefer-arrow-callback.js b/tools/node_modules/eslint/lib/rules/prefer-arrow-callback.js new file mode 100644 index 0000000000..31ae2859fe --- /dev/null +++ b/tools/node_modules/eslint/lib/rules/prefer-arrow-callback.js @@ -0,0 +1,304 @@ +/** + * @fileoverview A rule to suggest using arrow functions as callbacks. + * @author Toru Nagashima + */ + +"use strict"; + +//------------------------------------------------------------------------------ +// Helpers +//------------------------------------------------------------------------------ + +/** + * Checks whether or not a given variable is a function name. + * @param {eslint-scope.Variable} variable - A variable to check. + * @returns {boolean} `true` if the variable is a function name. + */ +function isFunctionName(variable) { + return variable && variable.defs[0].type === "FunctionName"; +} + +/** + * Checks whether or not a given MetaProperty node equals to a given value. + * @param {ASTNode} node - A MetaProperty node to check. + * @param {string} metaName - The name of `MetaProperty.meta`. + * @param {string} propertyName - The name of `MetaProperty.property`. + * @returns {boolean} `true` if the node is the specific value. + */ +function checkMetaProperty(node, metaName, propertyName) { + return node.meta.name === metaName && node.property.name === propertyName; +} + +/** + * Gets the variable object of `arguments` which is defined implicitly. + * @param {eslint-scope.Scope} scope - A scope to get. + * @returns {eslint-scope.Variable} The found variable object. + */ +function getVariableOfArguments(scope) { + const variables = scope.variables; + + for (let i = 0; i < variables.length; ++i) { + const variable = variables[i]; + + if (variable.name === "arguments") { + + /* + * If there was a parameter which is named "arguments", the + * implicit "arguments" is not defined. + * So does fast return with null. + */ + return (variable.identifiers.length === 0) ? variable : null; + } + } + + /* istanbul ignore next */ + return null; +} + +/** + * Checkes whether or not a given node is a callback. + * @param {ASTNode} node - A node to check. + * @returns {Object} + * {boolean} retv.isCallback - `true` if the node is a callback. + * {boolean} retv.isLexicalThis - `true` if the node is with `.bind(this)`. + */ +function getCallbackInfo(node) { + const retv = { isCallback: false, isLexicalThis: false }; + let parent = node.parent; + + while (node) { + switch (parent.type) { + + // Checks parents recursively. + + case "LogicalExpression": + case "ConditionalExpression": + break; + + // Checks whether the parent node is `.bind(this)` call. + case "MemberExpression": + if (parent.object === node && + !parent.property.computed && + parent.property.type === "Identifier" && + parent.property.name === "bind" && + parent.parent.type === "CallExpression" && + parent.parent.callee === parent + ) { + retv.isLexicalThis = ( + parent.parent.arguments.length === 1 && + parent.parent.arguments[0].type === "ThisExpression" + ); + parent = parent.parent; + } else { + return retv; + } + break; + + // Checks whether the node is a callback. + case "CallExpression": + case "NewExpression": + if (parent.callee !== node) { + retv.isCallback = true; + } + return retv; + + default: + return retv; + } + + node = parent; + parent = parent.parent; + } + + /* istanbul ignore next */ + throw new Error("unreachable"); +} + +/** + * Checks whether a simple list of parameters contains any duplicates. This does not handle complex + * parameter lists (e.g. with destructuring), since complex parameter lists are a SyntaxError with duplicate + * parameter names anyway. Instead, it always returns `false` for complex parameter lists. + * @param {ASTNode[]} paramsList The list of parameters for a function + * @returns {boolean} `true` if the list of parameters contains any duplicates + */ +function hasDuplicateParams(paramsList) { + return paramsList.every(param => param.type === "Identifier") && paramsList.length !== new Set(paramsList.map(param => param.name)).size; +} + +//------------------------------------------------------------------------------ +// Rule Definition +//------------------------------------------------------------------------------ + +module.exports = { + meta: { + docs: { + description: "require using arrow functions for callbacks", + category: "ECMAScript 6", + recommended: false + }, + + schema: [ + { + type: "object", + properties: { + allowNamedFunctions: { + type: "boolean" + }, + allowUnboundThis: { + type: "boolean" + } + }, + additionalProperties: false + } + ], + + fixable: "code" + }, + + create(context) { + const options = context.options[0] || {}; + + const allowUnboundThis = options.allowUnboundThis !== false; // default to true + const allowNamedFunctions = options.allowNamedFunctions; + const sourceCode = context.getSourceCode(); + + /* + * {Array<{this: boolean, super: boolean, meta: boolean}>} + * - this - A flag which shows there are one or more ThisExpression. + * - super - A flag which shows there are one or more Super. + * - meta - A flag which shows there are one or more MethProperty. + */ + let stack = []; + + /** + * Pushes new function scope with all `false` flags. + * @returns {void} + */ + function enterScope() { + stack.push({ this: false, super: false, meta: false }); + } + + /** + * Pops a function scope from the stack. + * @returns {{this: boolean, super: boolean, meta: boolean}} The information of the last scope. + */ + function exitScope() { + return stack.pop(); + } + + return { + + // Reset internal state. + Program() { + stack = []; + }, + + // If there are below, it cannot replace with arrow functions merely. + ThisExpression() { + const info = stack[stack.length - 1]; + + if (info) { + info.this = true; + } + }, + + Super() { + const info = stack[stack.length - 1]; + + if (info) { + info.super = true; + } + }, + + MetaProperty(node) { + const info = stack[stack.length - 1]; + + if (info && checkMetaProperty(node, "new", "target")) { + info.meta = true; + } + }, + + // To skip nested scopes. + FunctionDeclaration: enterScope, + "FunctionDeclaration:exit": exitScope, + + // Main. + FunctionExpression: enterScope, + "FunctionExpression:exit"(node) { + const scopeInfo = exitScope(); + + // Skip named function expressions + if (allowNamedFunctions && node.id && node.id.name) { + return; + } + + // Skip generators. + if (node.generator) { + return; + } + + // Skip recursive functions. + const nameVar = context.getDeclaredVariables(node)[0]; + + if (isFunctionName(nameVar) && nameVar.references.length > 0) { + return; + } + + // Skip if it's using arguments. + const variable = getVariableOfArguments(context.getScope()); + + if (variable && variable.references.length > 0) { + return; + } + + // Reports if it's a callback which can replace with arrows. + const callbackInfo = getCallbackInfo(node); + + if (callbackInfo.isCallback && + (!allowUnboundThis || !scopeInfo.this || callbackInfo.isLexicalThis) && + !scopeInfo.super && + !scopeInfo.meta + ) { + context.report({ + node, + message: "Unexpected function expression.", + fix(fixer) { + if ((!callbackInfo.isLexicalThis && scopeInfo.this) || hasDuplicateParams(node.params)) { + + /* + * If the callback function does not have .bind(this) and contains a reference to `this`, there + * is no way to determine what `this` should be, so don't perform any fixes. + * If the callback function has duplicates in its list of parameters (possible in sloppy mode), + * don't replace it with an arrow function, because this is a SyntaxError with arrow functions. + */ + return null; + } + + const paramsLeftParen = node.params.length ? sourceCode.getTokenBefore(node.params[0]) : sourceCode.getTokenBefore(node.body, 1); + const paramsRightParen = sourceCode.getTokenBefore(node.body); + const asyncKeyword = node.async ? "async " : ""; + const paramsFullText = sourceCode.text.slice(paramsLeftParen.range[0], paramsRightParen.range[1]); + const arrowFunctionText = `${asyncKeyword}${paramsFullText} => ${sourceCode.getText(node.body)}`; + + /* + * If the callback function has `.bind(this)`, replace it with an arrow function and remove the binding. + * Otherwise, just replace the arrow function itself. + */ + const replacedNode = callbackInfo.isLexicalThis ? node.parent.parent : node; + + /* + * If the replaced node is part of a BinaryExpression, LogicalExpression, or MemberExpression, then + * the arrow function needs to be parenthesized, because `foo || () => {}` is invalid syntax even + * though `foo || function() {}` is valid. + */ + const needsParens = replacedNode.parent.type !== "CallExpression" && replacedNode.parent.type !== "ConditionalExpression"; + const replacementText = needsParens ? `(${arrowFunctionText})` : arrowFunctionText; + + return fixer.replaceText(replacedNode, replacementText); + } + }); + } + } + }; + } +}; |