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@@ -0,0 +1,277 @@
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+/**
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+ * @fileoverview Rule to flag dangling underscores in variable declarations.
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+ * @author Matt DuVall <http://www.mattduvall.com>
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+ */
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+
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+"use strict";
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+
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+//------------------------------------------------------------------------------
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+// Rule Definition
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+//------------------------------------------------------------------------------
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+
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+module.exports = {
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+ meta: {
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+ type: "suggestion",
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+
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+ docs: {
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+ description: "disallow dangling underscores in identifiers",
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+ category: "Stylistic Issues",
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+ recommended: false,
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+ url: "https://eslint.org/docs/rules/no-underscore-dangle"
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+ },
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+
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+ schema: [
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+ {
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+ type: "object",
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+ properties: {
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+ allow: {
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+ type: "array",
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+ items: {
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+ type: "string"
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+ }
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+ },
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+ allowAfterThis: {
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+ type: "boolean",
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+ default: false
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+ },
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+ allowAfterSuper: {
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+ type: "boolean",
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+ default: false
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+ },
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+ allowAfterThisConstructor: {
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+ type: "boolean",
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+ default: false
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+ },
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+ enforceInMethodNames: {
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+ type: "boolean",
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+ default: false
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+ },
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+ allowFunctionParams: {
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+ type: "boolean",
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+ default: true
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+ }
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+ },
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+ additionalProperties: false
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+ }
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+ ],
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+
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+ messages: {
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+ unexpectedUnderscore: "Unexpected dangling '_' in '{{identifier}}'."
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+ }
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+ },
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+
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+ create(context) {
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+
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+ const options = context.options[0] || {};
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+ const ALLOWED_VARIABLES = options.allow ? options.allow : [];
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+ const allowAfterThis = typeof options.allowAfterThis !== "undefined" ? options.allowAfterThis : false;
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+ const allowAfterSuper = typeof options.allowAfterSuper !== "undefined" ? options.allowAfterSuper : false;
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+ const allowAfterThisConstructor = typeof options.allowAfterThisConstructor !== "undefined" ? options.allowAfterThisConstructor : false;
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+ const enforceInMethodNames = typeof options.enforceInMethodNames !== "undefined" ? options.enforceInMethodNames : false;
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+ const allowFunctionParams = typeof options.allowFunctionParams !== "undefined" ? options.allowFunctionParams : true;
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+
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+ //-------------------------------------------------------------------------
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+ // Helpers
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+ //-------------------------------------------------------------------------
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+
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+ /**
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+ * Check if identifier is present inside the allowed option
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+ * @param {string} identifier name of the node
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+ * @returns {boolean} true if its is present
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+ * @private
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+ */
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+ function isAllowed(identifier) {
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+ return ALLOWED_VARIABLES.some(ident => ident === identifier);
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+ }
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+
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+ /**
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+ * Check if identifier has a dangling underscore
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+ * @param {string} identifier name of the node
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+ * @returns {boolean} true if its is present
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+ * @private
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+ */
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+ function hasDanglingUnderscore(identifier) {
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+ const len = identifier.length;
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+
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+ return identifier !== "_" && (identifier[0] === "_" || identifier[len - 1] === "_");
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+ }
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+
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+ /**
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+ * Check if identifier is a special case member expression
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+ * @param {string} identifier name of the node
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+ * @returns {boolean} true if its is a special case
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+ * @private
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+ */
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+ function isSpecialCaseIdentifierForMemberExpression(identifier) {
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+ return identifier === "__proto__";
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+ }
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+
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+ /**
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+ * Check if identifier is a special case variable expression
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+ * @param {string} identifier name of the node
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+ * @returns {boolean} true if its is a special case
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+ * @private
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+ */
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+ function isSpecialCaseIdentifierInVariableExpression(identifier) {
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+
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+ // Checks for the underscore library usage here
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+ return identifier === "_";
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+ }
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+
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+ /**
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+ * Check if a node is a member reference of this.constructor
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+ * @param {ASTNode} node node to evaluate
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+ * @returns {boolean} true if it is a reference on this.constructor
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+ * @private
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+ */
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+ function isThisConstructorReference(node) {
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+ return node.object.type === "MemberExpression" &&
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+ node.object.property.name === "constructor" &&
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+ node.object.object.type === "ThisExpression";
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+ }
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+
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+ /**
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+ * Check if function parameter has a dangling underscore.
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+ * @param {ASTNode} node function node to evaluate
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+ * @returns {void}
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+ * @private
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+ */
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+ function checkForDanglingUnderscoreInFunctionParameters(node) {
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+ if (!allowFunctionParams) {
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+ node.params.forEach(param => {
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+ const { type } = param;
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+ let nodeToCheck;
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+
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+ if (type === "RestElement") {
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+ nodeToCheck = param.argument;
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+ } else if (type === "AssignmentPattern") {
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+ nodeToCheck = param.left;
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+ } else {
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+ nodeToCheck = param;
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+ }
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+
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+ if (nodeToCheck.type === "Identifier") {
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+ const identifier = nodeToCheck.name;
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+
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+ if (hasDanglingUnderscore(identifier) && !isAllowed(identifier)) {
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+ context.report({
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+ node: param,
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+ messageId: "unexpectedUnderscore",
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+ data: {
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+ identifier
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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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+
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+ /**
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+ * Check if function has a dangling underscore
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+ * @param {ASTNode} node node to evaluate
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+ * @returns {void}
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+ * @private
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+ */
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+ function checkForDanglingUnderscoreInFunction(node) {
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+ if (node.type === "FunctionDeclaration" && node.id) {
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+ const identifier = node.id.name;
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+
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+ if (typeof identifier !== "undefined" && hasDanglingUnderscore(identifier) && !isAllowed(identifier)) {
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+ context.report({
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+ node,
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+ messageId: "unexpectedUnderscore",
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+ data: {
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+ identifier
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+ }
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+ });
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+ }
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+ }
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+ checkForDanglingUnderscoreInFunctionParameters(node);
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+ }
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+
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+ /**
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+ * Check if variable expression has a dangling underscore
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+ * @param {ASTNode} node node to evaluate
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+ * @returns {void}
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+ * @private
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+ */
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+ function checkForDanglingUnderscoreInVariableExpression(node) {
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+ const identifier = node.id.name;
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+
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+ if (typeof identifier !== "undefined" && hasDanglingUnderscore(identifier) &&
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+ !isSpecialCaseIdentifierInVariableExpression(identifier) && !isAllowed(identifier)) {
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+ context.report({
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+ node,
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+ messageId: "unexpectedUnderscore",
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+ data: {
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+ identifier
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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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+ * Check if member expression has a dangling underscore
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+ * @param {ASTNode} node node to evaluate
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+ * @returns {void}
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+ * @private
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+ */
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+ function checkForDanglingUnderscoreInMemberExpression(node) {
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+ const identifier = node.property.name,
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+ isMemberOfThis = node.object.type === "ThisExpression",
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+ isMemberOfSuper = node.object.type === "Super",
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+ isMemberOfThisConstructor = isThisConstructorReference(node);
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+
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+ if (typeof identifier !== "undefined" && hasDanglingUnderscore(identifier) &&
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+ !(isMemberOfThis && allowAfterThis) &&
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+ !(isMemberOfSuper && allowAfterSuper) &&
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+ !(isMemberOfThisConstructor && allowAfterThisConstructor) &&
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+ !isSpecialCaseIdentifierForMemberExpression(identifier) && !isAllowed(identifier)) {
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+ context.report({
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+ node,
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+ messageId: "unexpectedUnderscore",
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+ data: {
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+ identifier
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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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+ * Check if method declaration or method property has a dangling underscore
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+ * @param {ASTNode} node node to evaluate
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+ * @returns {void}
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+ * @private
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+ */
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+ function checkForDanglingUnderscoreInMethod(node) {
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+ const identifier = node.key.name;
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+ const isMethod = node.type === "MethodDefinition" || node.type === "Property" && node.method;
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+
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+ if (typeof identifier !== "undefined" && enforceInMethodNames && isMethod && hasDanglingUnderscore(identifier) && !isAllowed(identifier)) {
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+ context.report({
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+ node,
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+ messageId: "unexpectedUnderscore",
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+ data: {
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+ identifier
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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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+ // Public API
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+ //--------------------------------------------------------------------------
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+
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+ return {
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+ FunctionDeclaration: checkForDanglingUnderscoreInFunction,
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+ VariableDeclarator: checkForDanglingUnderscoreInVariableExpression,
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+ MemberExpression: checkForDanglingUnderscoreInMemberExpression,
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+ MethodDefinition: checkForDanglingUnderscoreInMethod,
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+ Property: checkForDanglingUnderscoreInMethod,
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+ FunctionExpression: checkForDanglingUnderscoreInFunction,
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+ ArrowFunctionExpression: checkForDanglingUnderscoreInFunction
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+ };
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+
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+ }
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+};
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