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/**
* @fileoverview Rule to enforce consistent naming of "this" context variables
* @author Raphael Pigulla
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "suggestion",
docs: {
description: "enforce consistent naming when capturing the current execution context",
category: "Stylistic Issues",
recommended: false,
url: "https://eslint.org/docs/rules/consistent-this"
},
schema: {
type: "array",
items: {
type: "string",
minLength: 1
},
uniqueItems: true
},
messages: {
aliasNotAssignedToThis: "Designated alias '{{name}}' is not assigned to 'this'.",
unexpectedAlias: "Unexpected alias '{{name}}' for 'this'."
}
},
create(context) {
let aliases = [];
if (context.options.length === 0) {
aliases.push("that");
} else {
aliases = context.options;
}
/**
* Reports that a variable declarator or assignment expression is assigning
* a non-'this' value to the specified alias.
* @param {ASTNode} node The assigning node.
* @param {string} name the name of the alias that was incorrectly used.
* @returns {void}
*/
function reportBadAssignment(node, name) {
context.report({ node, messageId: "aliasNotAssignedToThis", data: { name } });
}
/**
* Checks that an assignment to an identifier only assigns 'this' to the
* appropriate alias, and the alias is only assigned to 'this'.
* @param {ASTNode} node The assigning node.
* @param {Identifier} name The name of the variable assigned to.
* @param {Expression} value The value of the assignment.
* @returns {void}
*/
function checkAssignment(node, name, value) {
const isThis = value.type === "ThisExpression";
if (aliases.indexOf(name) !== -1) {
if (!isThis || node.operator && node.operator !== "=") {
reportBadAssignment(node, name);
}
} else if (isThis) {
context.report({ node, messageId: "unexpectedAlias", data: { name } });
}
}
/**
* Ensures that a variable declaration of the alias in a program or function
* is assigned to the correct value.
* @param {string} alias alias the check the assignment of.
* @param {Object} scope scope of the current code we are checking.
* @private
* @returns {void}
*/
function checkWasAssigned(alias, scope) {
const variable = scope.set.get(alias);
if (!variable) {
return;
}
if (variable.defs.some(def => def.node.type === "VariableDeclarator" &&
def.node.init !== null)) {
return;
}
/*
* The alias has been declared and not assigned: check it was
* assigned later in the same scope.
*/
if (!variable.references.some(reference => {
const write = reference.writeExpr;
return (
reference.from === scope &&
write && write.type === "ThisExpression" &&
write.parent.operator === "="
);
})) {
variable.defs.map(def => def.node).forEach(node => {
reportBadAssignment(node, alias);
});
}
}
/**
* Check each alias to ensure that is was assinged to the correct value.
* @returns {void}
*/
function ensureWasAssigned() {
const scope = context.getScope();
aliases.forEach(alias => {
checkWasAssigned(alias, scope);
});
}
return {
"Program:exit": ensureWasAssigned,
"FunctionExpression:exit": ensureWasAssigned,
"FunctionDeclaration:exit": ensureWasAssigned,
VariableDeclarator(node) {
const id = node.id;
const isDestructuring =
id.type === "ArrayPattern" || id.type === "ObjectPattern";
if (node.init !== null && !isDestructuring) {
checkAssignment(node, id.name, node.init);
}
},
AssignmentExpression(node) {
if (node.left.type === "Identifier") {
checkAssignment(node, node.left.name, node.right);
}
}
};
}
};
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