no-unnecessary-boolean-literal-compare.js
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"use strict";
var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
if (k2 === undefined) k2 = k;
Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
}) : (function(o, m, k, k2) {
if (k2 === undefined) k2 = k;
o[k2] = m[k];
}));
var __setModuleDefault = (this && this.__setModuleDefault) || (Object.create ? (function(o, v) {
Object.defineProperty(o, "default", { enumerable: true, value: v });
}) : function(o, v) {
o["default"] = v;
});
var __importStar = (this && this.__importStar) || function (mod) {
if (mod && mod.__esModule) return mod;
var result = {};
if (mod != null) for (var k in mod) if (k !== "default" && Object.prototype.hasOwnProperty.call(mod, k)) __createBinding(result, mod, k);
__setModuleDefault(result, mod);
return result;
};
Object.defineProperty(exports, "__esModule", { value: true });
const experimental_utils_1 = require("@typescript-eslint/experimental-utils");
const tsutils = __importStar(require("tsutils"));
const ts = __importStar(require("typescript"));
const util = __importStar(require("../util"));
exports.default = util.createRule({
name: 'no-unnecessary-boolean-literal-compare',
meta: {
docs: {
description: 'Flags unnecessary equality comparisons against boolean literals',
category: 'Stylistic Issues',
recommended: false,
requiresTypeChecking: true,
},
fixable: 'code',
messages: {
direct: 'This expression unnecessarily compares a boolean value to a boolean instead of using it directly.',
negated: 'This expression unnecessarily compares a boolean value to a boolean instead of negating it.',
comparingNullableToTrueDirect: 'This expression unnecessarily compares a nullable boolean value to true instead of using it directly.',
comparingNullableToTrueNegated: 'This expression unnecessarily compares a nullable boolean value to true instead of negating it.',
comparingNullableToFalse: 'This expression unnecessarily compares a nullable boolean value to false instead of using the ?? operator to provide a default.',
},
schema: [
{
type: 'object',
properties: {
allowComparingNullableBooleansToTrue: {
type: 'boolean',
},
allowComparingNullableBooleansToFalse: {
type: 'boolean',
},
},
additionalProperties: false,
},
],
type: 'suggestion',
},
defaultOptions: [
{
allowComparingNullableBooleansToTrue: true,
allowComparingNullableBooleansToFalse: true,
},
],
create(context, [options]) {
const parserServices = util.getParserServices(context);
const checker = parserServices.program.getTypeChecker();
function getBooleanComparison(node) {
const comparison = deconstructComparison(node);
if (!comparison) {
return undefined;
}
const expressionType = checker.getTypeAtLocation(parserServices.esTreeNodeToTSNodeMap.get(comparison.expression));
if (isBooleanType(expressionType)) {
return Object.assign(Object.assign({}, comparison), { expressionIsNullableBoolean: false });
}
if (isNullableBoolean(expressionType)) {
return Object.assign(Object.assign({}, comparison), { expressionIsNullableBoolean: true });
}
return undefined;
}
function isBooleanType(expressionType) {
return tsutils.isTypeFlagSet(expressionType, ts.TypeFlags.Boolean | ts.TypeFlags.BooleanLiteral);
}
/**
* checks if the expressionType is a union that
* 1) contains at least one nullish type (null or undefined)
* 2) contains at least once boolean type (true or false or boolean)
* 3) does not contain any types besides nullish and boolean types
*/
function isNullableBoolean(expressionType) {
if (!expressionType.isUnion()) {
return false;
}
const { types } = expressionType;
const nonNullishTypes = types.filter(type => !tsutils.isTypeFlagSet(type, ts.TypeFlags.Undefined | ts.TypeFlags.Null));
const hasNonNullishType = nonNullishTypes.length > 0;
if (!hasNonNullishType) {
return false;
}
const hasNullableType = nonNullishTypes.length < types.length;
if (!hasNullableType) {
return false;
}
const allNonNullishTypesAreBoolean = nonNullishTypes.every(isBooleanType);
if (!allNonNullishTypesAreBoolean) {
return false;
}
return true;
}
function deconstructComparison(node) {
const comparisonType = util.getEqualsKind(node.operator);
if (!comparisonType) {
return undefined;
}
for (const [against, expression] of [
[node.right, node.left],
[node.left, node.right],
]) {
if (against.type !== experimental_utils_1.AST_NODE_TYPES.Literal ||
typeof against.value !== 'boolean') {
continue;
}
const { value: literalBooleanInComparison } = against;
const negated = !comparisonType.isPositive;
return {
literalBooleanInComparison,
forTruthy: literalBooleanInComparison ? !negated : negated,
expression,
negated,
range: expression.range[0] < against.range[0]
? [expression.range[1], against.range[1]]
: [against.range[1], expression.range[1]],
};
}
return undefined;
}
function nodeIsUnaryNegation(node) {
return (node.type === experimental_utils_1.AST_NODE_TYPES.UnaryExpression &&
node.prefix &&
node.operator === '!');
}
return {
BinaryExpression(node) {
const comparison = getBooleanComparison(node);
if (comparison === undefined) {
return;
}
if (comparison.expressionIsNullableBoolean) {
if (comparison.literalBooleanInComparison &&
options.allowComparingNullableBooleansToTrue) {
return;
}
if (!comparison.literalBooleanInComparison &&
options.allowComparingNullableBooleansToFalse) {
return;
}
}
context.report({
fix: function* (fixer) {
yield fixer.removeRange(comparison.range);
// if the expression `exp` isn't nullable, or we're comparing to `true`,
// we can just replace the entire comparison with `exp` or `!exp`
if (!comparison.expressionIsNullableBoolean ||
comparison.literalBooleanInComparison) {
if (!comparison.forTruthy) {
yield fixer.insertTextBefore(node, '!');
}
return;
}
// if we're here, then the expression is a nullable boolean and we're
// comparing to a literal `false`
// if we're doing `== false` or `=== false`, then we need to negate the expression
if (!comparison.negated) {
const { parent } = node;
// if the parent is a negation, we can instead just get rid of the parent's negation.
// i.e. instead of resulting in `!(!(exp))`, we can just result in `exp`
if (parent != null && nodeIsUnaryNegation(parent)) {
// remove from the beginning of the parent to the beginning of this node
yield fixer.removeRange([parent.range[0], node.range[0]]);
// remove from the end of the node to the end of the parent
yield fixer.removeRange([node.range[1], parent.range[1]]);
}
else {
yield fixer.insertTextBefore(node, '!');
}
}
// provide the default `true`
yield fixer.insertTextBefore(node, '(');
yield fixer.insertTextAfter(node, ' ?? true)');
},
messageId: comparison.expressionIsNullableBoolean
? comparison.literalBooleanInComparison
? comparison.negated
? 'comparingNullableToTrueNegated'
: 'comparingNullableToTrueDirect'
: 'comparingNullableToFalse'
: comparison.negated
? 'negated'
: 'direct',
node,
});
},
};
},
});
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