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