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Diffstat (limited to 'tools/node_modules/eslint/lib/rules/no-return-await.js')
-rw-r--r-- | tools/node_modules/eslint/lib/rules/no-return-await.js | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/tools/node_modules/eslint/lib/rules/no-return-await.js b/tools/node_modules/eslint/lib/rules/no-return-await.js new file mode 100644 index 0000000000..2f06b61108 --- /dev/null +++ b/tools/node_modules/eslint/lib/rules/no-return-await.js @@ -0,0 +1,94 @@ +/** + * @fileoverview Disallows unnecessary `return await` + * @author Jordan Harband + */ +"use strict"; + +const astUtils = require("../ast-utils"); + +//------------------------------------------------------------------------------ +// Rule Definition +//------------------------------------------------------------------------------ + +const message = "Redundant use of `await` on a return value."; + +module.exports = { + meta: { + docs: { + description: "disallow unnecessary `return await`", + category: "Best Practices", + recommended: false // TODO: set to true + }, + 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); + } + } + }; + } +}; |