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/**
* @fileoverview A rule to disallow the type conversions with shorter notations.
* @author Toru Nagashima
*/
"use strict";
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const INDEX_OF_PATTERN = /^(?:i|lastI)ndexOf$/u;
const ALLOWABLE_OPERATORS = ["~", "!!", "+", "- -", "-", "*"];
/**
* Checks whether or not a node is a double logical negating.
* @param {ASTNode} node An UnaryExpression node to check.
* @returns {boolean} Whether or not the node is a double logical negating.
*/
function isDoubleLogicalNegating(node) {
return (
node.operator === "!" &&
node.argument.type === "UnaryExpression" &&
node.argument.operator === "!"
);
}
/**
* Checks whether or not a node is a binary negating of `.indexOf()` method calling.
* @param {ASTNode} node An UnaryExpression node to check.
* @returns {boolean} Whether or not the node is a binary negating of `.indexOf()` method calling.
*/
function isBinaryNegatingOfIndexOf(node) {
if (node.operator !== "~") {
return false;
}
const callNode = astUtils.skipChainExpression(node.argument);
return (
callNode.type === "CallExpression" &&
astUtils.isSpecificMemberAccess(callNode.callee, null, INDEX_OF_PATTERN)
);
}
/**
* Checks whether or not a node is a multiplying by one.
* @param {BinaryExpression} node A BinaryExpression node to check.
* @returns {boolean} Whether or not the node is a multiplying by one.
*/
function isMultiplyByOne(node) {
return (
node.operator === "*" &&
((node.left.type === "Literal" && node.left.value === 1) ||
(node.right.type === "Literal" && node.right.value === 1))
);
}
/**
* Checks whether the given node logically represents multiplication by a fraction of `1`.
* For example, `a * 1` in `a * 1 / b` is technically multiplication by `1`, but the
* whole expression can be logically interpreted as `a * (1 / b)` rather than `(a * 1) / b`.
* @param {BinaryExpression} node A BinaryExpression node to check.
* @param {SourceCode} sourceCode The source code object.
* @returns {boolean} Whether or not the node is a multiplying by a fraction of `1`.
*/
function isMultiplyByFractionOfOne(node, sourceCode) {
return (
node.type === "BinaryExpression" &&
node.operator === "*" &&
node.right.type === "Literal" &&
node.right.value === 1 &&
node.parent.type === "BinaryExpression" &&
node.parent.operator === "/" &&
node.parent.left === node &&
!astUtils.isParenthesised(sourceCode, node)
);
}
/**
* Checks whether the result of a node is numeric or not
* @param {ASTNode} node The node to test
* @returns {boolean} true if the node is a number literal or a `Number()`, `parseInt` or `parseFloat` call
*/
function isNumeric(node) {
return (
(node.type === "Literal" && typeof node.value === "number") ||
(node.type === "CallExpression" &&
(node.callee.name === "Number" ||
node.callee.name === "parseInt" ||
node.callee.name === "parseFloat"))
);
}
/**
* Returns the first non-numeric operand in a BinaryExpression. Designed to be
* used from bottom to up since it walks up the BinaryExpression trees using
* node.parent to find the result.
* @param {BinaryExpression} node The BinaryExpression node to be walked up on
* @returns {ASTNode|null} The first non-numeric item in the BinaryExpression tree or null
*/
function getNonNumericOperand(node) {
const left = node.left,
right = node.right;
if (right.type !== "BinaryExpression" && !isNumeric(right)) {
return right;
}
if (left.type !== "BinaryExpression" && !isNumeric(left)) {
return left;
}
return null;
}
/**
* Checks whether an expression evaluates to a string.
* @param {ASTNode} node node that represents the expression to check.
* @returns {boolean} Whether or not the expression evaluates to a string.
*/
function isStringType(node) {
return (
astUtils.isStringLiteral(node) ||
(node.type === "CallExpression" &&
node.callee.type === "Identifier" &&
node.callee.name === "String")
);
}
/**
* Checks whether a node is an empty string literal or not.
* @param {ASTNode} node The node to check.
* @returns {boolean} Whether or not the passed in node is an
* empty string literal or not.
*/
function isEmptyString(node) {
return (
astUtils.isStringLiteral(node) &&
(node.value === "" ||
(node.type === "TemplateLiteral" &&
node.quasis.length === 1 &&
node.quasis[0].value.cooked === ""))
);
}
/**
* Checks whether or not a node is a concatenating with an empty string.
* @param {ASTNode} node A BinaryExpression node to check.
* @returns {boolean} Whether or not the node is a concatenating with an empty string.
*/
function isConcatWithEmptyString(node) {
return (
node.operator === "+" &&
((isEmptyString(node.left) && !isStringType(node.right)) ||
(isEmptyString(node.right) && !isStringType(node.left)))
);
}
/**
* Checks whether or not a node is appended with an empty string.
* @param {ASTNode} node An AssignmentExpression node to check.
* @returns {boolean} Whether or not the node is appended with an empty string.
*/
function isAppendEmptyString(node) {
return node.operator === "+=" && isEmptyString(node.right);
}
/**
* Returns the operand that is not an empty string from a flagged BinaryExpression.
* @param {ASTNode} node The flagged BinaryExpression node to check.
* @returns {ASTNode} The operand that is not an empty string from a flagged BinaryExpression.
*/
function getNonEmptyOperand(node) {
return isEmptyString(node.left) ? node.right : node.left;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../types').Rule.RuleModule} */
module.exports = {
meta: {
hasSuggestions: true,
type: "suggestion",
docs: {
description: "Disallow shorthand type conversions",
recommended: false,
frozen: true,
url: "https://eslint.org/docs/latest/rules/no-implicit-coercion",
},
fixable: "code",
schema: [
{
type: "object",
properties: {
boolean: {
type: "boolean",
},
number: {
type: "boolean",
},
string: {
type: "boolean",
},
disallowTemplateShorthand: {
type: "boolean",
},
allow: {
type: "array",
items: {
enum: ALLOWABLE_OPERATORS,
},
uniqueItems: true,
},
},
additionalProperties: false,
},
],
defaultOptions: [
{
allow: [],
boolean: true,
disallowTemplateShorthand: false,
number: true,
string: true,
},
],
messages: {
implicitCoercion:
"Unexpected implicit coercion encountered. Use `{{recommendation}}` instead.",
useRecommendation: "Use `{{recommendation}}` instead.",
},
},
create(context) {
const [options] = context.options;
const sourceCode = context.sourceCode;
/**
* Reports an error and autofixes the node
* @param {ASTNode} node An ast node to report the error on.
* @param {string} recommendation The recommended code for the issue
* @param {bool} shouldSuggest Whether this report should offer a suggestion
* @param {bool} shouldFix Whether this report should fix the node
* @returns {void}
*/
function report(node, recommendation, shouldSuggest, shouldFix) {
/**
* Fix function
* @param {RuleFixer} fixer The fixer to fix.
* @returns {Fix} The fix object.
*/
function fix(fixer) {
const tokenBefore = sourceCode.getTokenBefore(node);
if (
tokenBefore?.range[1] === node.range[0] &&
!astUtils.canTokensBeAdjacent(tokenBefore, recommendation)
) {
return fixer.replaceText(node, ` ${recommendation}`);
}
return fixer.replaceText(node, recommendation);
}
context.report({
node,
messageId: "implicitCoercion",
data: { recommendation },
fix(fixer) {
if (!shouldFix) {
return null;
}
return fix(fixer);
},
suggest: [
{
messageId: "useRecommendation",
data: { recommendation },
fix(fixer) {
if (shouldFix || !shouldSuggest) {
return null;
}
return fix(fixer);
},
},
],
});
}
return {
UnaryExpression(node) {
let operatorAllowed;
// !!foo
operatorAllowed = options.allow.includes("!!");
if (
!operatorAllowed &&
options.boolean &&
isDoubleLogicalNegating(node)
) {
const recommendation = `Boolean(${sourceCode.getText(node.argument.argument)})`;
const variable = astUtils.getVariableByName(
sourceCode.getScope(node),
"Boolean",
);
const booleanExists = variable?.identifiers.length === 0;
report(node, recommendation, true, booleanExists);
}
// ~foo.indexOf(bar)
operatorAllowed = options.allow.includes("~");
if (
!operatorAllowed &&
options.boolean &&
isBinaryNegatingOfIndexOf(node)
) {
// `foo?.indexOf(bar) !== -1` will be true (== found) if the `foo` is nullish. So use `>= 0` in that case.
const comparison =
node.argument.type === "ChainExpression"
? ">= 0"
: "!== -1";
const recommendation = `${sourceCode.getText(node.argument)} ${comparison}`;
report(node, recommendation, false, false);
}
// +foo
operatorAllowed = options.allow.includes("+");
if (
!operatorAllowed &&
options.number &&
node.operator === "+" &&
!isNumeric(node.argument)
) {
const recommendation = `Number(${sourceCode.getText(node.argument)})`;
report(node, recommendation, true, false);
}
// -(-foo)
operatorAllowed = options.allow.includes("- -");
if (
!operatorAllowed &&
options.number &&
node.operator === "-" &&
node.argument.type === "UnaryExpression" &&
node.argument.operator === "-" &&
!isNumeric(node.argument.argument)
) {
const recommendation = `Number(${sourceCode.getText(node.argument.argument)})`;
report(node, recommendation, true, false);
}
},
// Use `:exit` to prevent double reporting
"BinaryExpression:exit"(node) {
let operatorAllowed;
// 1 * foo
operatorAllowed = options.allow.includes("*");
const nonNumericOperand =
!operatorAllowed &&
options.number &&
isMultiplyByOne(node) &&
!isMultiplyByFractionOfOne(node, sourceCode) &&
getNonNumericOperand(node);
if (nonNumericOperand) {
const recommendation = `Number(${sourceCode.getText(nonNumericOperand)})`;
report(node, recommendation, true, false);
}
// foo - 0
operatorAllowed = options.allow.includes("-");
if (
!operatorAllowed &&
options.number &&
node.operator === "-" &&
node.right.type === "Literal" &&
node.right.value === 0 &&
!isNumeric(node.left)
) {
const recommendation = `Number(${sourceCode.getText(node.left)})`;
report(node, recommendation, true, false);
}
// "" + foo
operatorAllowed = options.allow.includes("+");
if (
!operatorAllowed &&
options.string &&
isConcatWithEmptyString(node)
) {
const recommendation = `String(${sourceCode.getText(getNonEmptyOperand(node))})`;
report(node, recommendation, true, false);
}
},
AssignmentExpression(node) {
// foo += ""
const operatorAllowed = options.allow.includes("+");
if (
!operatorAllowed &&
options.string &&
isAppendEmptyString(node)
) {
const code = sourceCode.getText(getNonEmptyOperand(node));
const recommendation = `${code} = String(${code})`;
report(node, recommendation, true, false);
}
},
TemplateLiteral(node) {
if (!options.disallowTemplateShorthand) {
return;
}
// tag`${foo}`
if (node.parent.type === "TaggedTemplateExpression") {
return;
}
// `` or `${foo}${bar}`
if (node.expressions.length !== 1) {
return;
}
// `prefix${foo}`
if (node.quasis[0].value.cooked !== "") {
return;
}
// `${foo}postfix`
if (node.quasis[1].value.cooked !== "") {
return;
}
// if the expression is already a string, then this isn't a coercion
if (isStringType(node.expressions[0])) {
return;
}
const code = sourceCode.getText(node.expressions[0]);
const recommendation = `String(${code})`;
report(node, recommendation, true, false);
},
};
},
};
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