tools: move eslint from tools to tools/node_modules

This is required because we need to add the babel-eslint dependency
and it has to be able to resolve "eslint".
babel-eslint is required to support future ES features such as async
iterators and import.meta.

Refs: https://github.com/nodejs/node/pull/17755
PR-URL: https://github.com/nodejs/node/pull/17820
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

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);
+                }
+            }
+        };
+    }
+};