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| /** | |
| * @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); | |
| } | |
| } | |
| }; | |
| } | |
| }; |