2 * @fileoverview Disallows unnecessary `return await`
3 * @author Jordan Harband
7 const astUtils = require("./utils/ast-utils");
9 //------------------------------------------------------------------------------
11 //------------------------------------------------------------------------------
18 description: "disallow unnecessary `return await`",
19 category: "Best Practices",
23 url: "https://eslint.org/docs/rules/no-return-await"
32 redundantUseOfAwait: "Redundant use of `await` on a return value."
39 * Reports a found unnecessary `await` expression.
40 * @param {ASTNode} node The node representing the `await` expression to report
43 function reportUnnecessaryAwait(node) {
45 node: context.getSourceCode().getFirstToken(node),
47 messageId: "redundantUseOfAwait"
52 * Determines whether a thrown error from this node will be caught/handled within this function rather than immediately halting
53 * this function. For example, a statement in a `try` block will always have an error handler. A statement in
54 * a `catch` block will only have an error handler if there is also a `finally` block.
55 * @param {ASTNode} node A node representing a location where an could be thrown
56 * @returns {boolean} `true` if a thrown error will be caught/handled in this function
58 function hasErrorHandler(node) {
61 while (!astUtils.isFunction(ancestor) && ancestor.type !== "Program") {
62 if (ancestor.parent.type === "TryStatement" && (ancestor === ancestor.parent.block || ancestor === ancestor.parent.handler && ancestor.parent.finalizer)) {
65 ancestor = ancestor.parent;
71 * Checks if a node is placed in tail call position. Once `return` arguments (or arrow function expressions) can be a complex expression,
72 * 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.
73 * @param {ASTNode} node A node representing the `await` expression to check
74 * @returns {boolean} The checking result
76 function isInTailCallPosition(node) {
77 if (node.parent.type === "ArrowFunctionExpression") {
80 if (node.parent.type === "ReturnStatement") {
81 return !hasErrorHandler(node.parent);
83 if (node.parent.type === "ConditionalExpression" && (node === node.parent.consequent || node === node.parent.alternate)) {
84 return isInTailCallPosition(node.parent);
86 if (node.parent.type === "LogicalExpression" && node === node.parent.right) {
87 return isInTailCallPosition(node.parent);
89 if (node.parent.type === "SequenceExpression" && node === node.parent.expressions[node.parent.expressions.length - 1]) {
90 return isInTailCallPosition(node.parent);
96 AwaitExpression(node) {
97 if (isInTailCallPosition(node) && !hasErrorHandler(node)) {
98 reportUnnecessaryAwait(node);