| /** |
| * @fileoverview Disallows unnecessary `return await` |
| * @author Jordan Harband |
| */ |
| "use strict"; |
| |
| const astUtils = require("./utils/ast-utils"); |
| |
| //------------------------------------------------------------------------------ |
| // Rule Definition |
| //------------------------------------------------------------------------------ |
| |
| const message = "Redundant use of `await` on a return value."; |
| |
| module.exports = { |
| meta: { |
| type: "suggestion", |
| |
| docs: { |
| description: "disallow unnecessary `return await`", |
| category: "Best Practices", |
| |
| recommended: false, |
| |
| url: "https://eslint.org/docs/rules/no-return-await" |
| }, |
| |
| fixable: null, |
| |
| schema: [ |
| ] |
| }, |
| |
| create(context) { |
| |
| /** |
| * Reports a found unnecessary `await` expression. |
| * @param {ASTNode} node The node representing the `await` expression to report |
| * @returns {void} |
| */ |
| function reportUnnecessaryAwait(node) { |
| context.report({ |
| node: context.getSourceCode().getFirstToken(node), |
| loc: node.loc, |
| message |
| }); |
| } |
| |
| /** |
| * Determines whether a thrown error from this node will be caught/handled within this function rather than immediately halting |
| * this function. For example, a statement in a `try` block will always have an error handler. A statement in |
| * a `catch` block will only have an error handler if there is also a `finally` block. |
| * @param {ASTNode} node A node representing a location where an could be thrown |
| * @returns {boolean} `true` if a thrown error will be caught/handled in this function |
| */ |
| function hasErrorHandler(node) { |
| let ancestor = node; |
| |
| while (!astUtils.isFunction(ancestor) && ancestor.type !== "Program") { |
| if (ancestor.parent.type === "TryStatement" && (ancestor === ancestor.parent.block || ancestor === ancestor.parent.handler && ancestor.parent.finalizer)) { |
| return true; |
| } |
| ancestor = ancestor.parent; |
| } |
| return false; |
| } |
| |
| /** |
| * Checks if a node is placed in tail call position. Once `return` arguments (or arrow function expressions) can be a complex expression, |
| * an `await` expression could or could not be unnecessary by the definition of this rule. So we're looking for `await` expressions that are in tail position. |
| * @param {ASTNode} node A node representing the `await` expression to check |
| * @returns {boolean} The checking result |
| */ |
| function isInTailCallPosition(node) { |
| if (node.parent.type === "ArrowFunctionExpression") { |
| return true; |
| } |
| if (node.parent.type === "ReturnStatement") { |
| return !hasErrorHandler(node.parent); |
| } |
| if (node.parent.type === "ConditionalExpression" && (node === node.parent.consequent || node === node.parent.alternate)) { |
| return isInTailCallPosition(node.parent); |
| } |
| if (node.parent.type === "LogicalExpression" && node === node.parent.right) { |
| return isInTailCallPosition(node.parent); |
| } |
| if (node.parent.type === "SequenceExpression" && node === node.parent.expressions[node.parent.expressions.length - 1]) { |
| return isInTailCallPosition(node.parent); |
| } |
| return false; |
| } |
| |
| return { |
| AwaitExpression(node) { |
| if (isInTailCallPosition(node) && !hasErrorHandler(node)) { |
| reportUnnecessaryAwait(node); |
| } |
| } |
| }; |
| } |
| }; |