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qwen/nodejs/node_modules/eslint/lib/rules/no-unused-private-class-members.js

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+/**
+ * @fileoverview Rule to flag declared but unused private class members
+ * @author Tim van der Lippe
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+/** @type {import('../shared/types').Rule} */
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "Disallow unused private class members",
+            recommended: false,
+            url: "https://eslint.org/docs/latest/rules/no-unused-private-class-members"
+        },
+
+        schema: [],
+
+        messages: {
+            unusedPrivateClassMember: "'{{classMemberName}}' is defined but never used."
+        }
+    },
+
+    create(context) {
+        const trackedClasses = [];
+
+        /**
+         * Check whether the current node is in a write only assignment.
+         * @param {ASTNode} privateIdentifierNode Node referring to a private identifier
+         * @returns {boolean} Whether the node is in a write only assignment
+         * @private
+         */
+        function isWriteOnlyAssignment(privateIdentifierNode) {
+            const parentStatement = privateIdentifierNode.parent.parent;
+            const isAssignmentExpression = parentStatement.type === "AssignmentExpression";
+
+            if (!isAssignmentExpression &&
+                parentStatement.type !== "ForInStatement" &&
+                parentStatement.type !== "ForOfStatement" &&
+                parentStatement.type !== "AssignmentPattern") {
+                return false;
+            }
+
+            // It is a write-only usage, since we still allow usages on the right for reads
+            if (parentStatement.left !== privateIdentifierNode.parent) {
+                return false;
+            }
+
+            // For any other operator (such as '+=') we still consider it a read operation
+            if (isAssignmentExpression && parentStatement.operator !== "=") {
+
+                /*
+                 * However, if the read operation is "discarded" in an empty statement, then
+                 * we consider it write only.
+                 */
+                return parentStatement.parent.type === "ExpressionStatement";
+            }
+
+            return true;
+        }
+
+        //--------------------------------------------------------------------------
+        // Public
+        //--------------------------------------------------------------------------
+
+        return {
+
+            // Collect all declared members up front and assume they are all unused
+            ClassBody(classBodyNode) {
+                const privateMembers = new Map();
+
+                trackedClasses.unshift(privateMembers);
+                for (const bodyMember of classBodyNode.body) {
+                    if (bodyMember.type === "PropertyDefinition" || bodyMember.type === "MethodDefinition") {
+                        if (bodyMember.key.type === "PrivateIdentifier") {
+                            privateMembers.set(bodyMember.key.name, {
+                                declaredNode: bodyMember,
+                                isAccessor: bodyMember.type === "MethodDefinition" &&
+                                    (bodyMember.kind === "set" || bodyMember.kind === "get")
+                            });
+                        }
+                    }
+                }
+            },
+
+            /*
+             * Process all usages of the private identifier and remove a member from
+             * `declaredAndUnusedPrivateMembers` if we deem it used.
+             */
+            PrivateIdentifier(privateIdentifierNode) {
+                const classBody = trackedClasses.find(classProperties => classProperties.has(privateIdentifierNode.name));
+
+                // Can't happen, as it is a parser to have a missing class body, but let's code defensively here.
+                if (!classBody) {
+                    return;
+                }
+
+                // In case any other usage was already detected, we can short circuit the logic here.
+                const memberDefinition = classBody.get(privateIdentifierNode.name);
+
+                if (memberDefinition.isUsed) {
+                    return;
+                }
+
+                // The definition of the class member itself
+                if (privateIdentifierNode.parent.type === "PropertyDefinition" ||
+                    privateIdentifierNode.parent.type === "MethodDefinition") {
+                    return;
+                }
+
+                /*
+                 * Any usage of an accessor is considered a read, as the getter/setter can have
+                 * side-effects in its definition.
+                 */
+                if (memberDefinition.isAccessor) {
+                    memberDefinition.isUsed = true;
+                    return;
+                }
+
+                // Any assignments to this member, except for assignments that also read
+                if (isWriteOnlyAssignment(privateIdentifierNode)) {
+                    return;
+                }
+
+                const wrappingExpressionType = privateIdentifierNode.parent.parent.type;
+                const parentOfWrappingExpressionType = privateIdentifierNode.parent.parent.parent.type;
+
+                // A statement which only increments (`this.#x++;`)
+                if (wrappingExpressionType === "UpdateExpression" &&
+                    parentOfWrappingExpressionType === "ExpressionStatement") {
+                    return;
+                }
+
+                /*
+                 * ({ x: this.#usedInDestructuring } = bar);
+                 *
+                 * But should treat the following as a read:
+                 * ({ [this.#x]: a } = foo);
+                 */
+                if (wrappingExpressionType === "Property" &&
+                    parentOfWrappingExpressionType === "ObjectPattern" &&
+                    privateIdentifierNode.parent.parent.value === privateIdentifierNode.parent) {
+                    return;
+                }
+
+                // [...this.#unusedInRestPattern] = bar;
+                if (wrappingExpressionType === "RestElement") {
+                    return;
+                }
+
+                // [this.#unusedInAssignmentPattern] = bar;
+                if (wrappingExpressionType === "ArrayPattern") {
+                    return;
+                }
+
+                /*
+                 * We can't delete the memberDefinition, as we need to keep track of which member we are marking as used.
+                 * In the case of nested classes, we only mark the first member we encounter as used. If you were to delete
+                 * the member, then any subsequent usage could incorrectly mark the member of an encapsulating parent class
+                 * as used, which is incorrect.
+                 */
+                memberDefinition.isUsed = true;
+            },
+
+            /*
+             * Post-process the class members and report any remaining members.
+             * Since private members can only be accessed in the current class context,
+             * we can safely assume that all usages are within the current class body.
+             */
+            "ClassBody:exit"() {
+                const unusedPrivateMembers = trackedClasses.shift();
+
+                for (const [classMemberName, { declaredNode, isUsed }] of unusedPrivateMembers.entries()) {
+                    if (isUsed) {
+                        continue;
+                    }
+                    context.report({
+                        node: declaredNode,
+                        loc: declaredNode.key.loc,
+                        messageId: "unusedPrivateClassMember",
+                        data: {
+                            classMemberName: `#${classMemberName}`
+                        }
+                    });
+                }
+            }
+        };
+    }
+};