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- /**
- * @fileoverview Disallows unnecessary `return await`
- * @author Jordan Harband
- */
- "use strict";
-
- const astUtils = require("../util/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);
- }
- }
- };
- }
- };
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