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strict-boolean-expressions.ts
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strict-boolean-expressions.ts
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import {
TSESTree,
AST_NODE_TYPES,
} from '@typescript-eslint/experimental-utils';
import * as ts from 'typescript';
import * as tsutils from 'tsutils';
import * as util from '../util';
export type Options = [
{
allowString?: boolean;
allowNumber?: boolean;
allowNullableObject?: boolean;
allowNullableBoolean?: boolean;
allowNullableString?: boolean;
allowNullableNumber?: boolean;
allowAny?: boolean;
allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing?: boolean;
},
];
export type MessageId =
| 'conditionErrorOther'
| 'conditionErrorAny'
| 'conditionErrorNullish'
| 'conditionErrorNullableBoolean'
| 'conditionErrorString'
| 'conditionErrorNullableString'
| 'conditionErrorNumber'
| 'conditionErrorNullableNumber'
| 'conditionErrorObject'
| 'conditionErrorNullableObject'
| 'noStrictNullCheck';
export default util.createRule<Options, MessageId>({
name: 'strict-boolean-expressions',
meta: {
type: 'suggestion',
docs: {
description: 'Restricts the types allowed in boolean expressions',
category: 'Best Practices',
recommended: false,
requiresTypeChecking: true,
},
schema: [
{
type: 'object',
properties: {
allowString: { type: 'boolean' },
allowNumber: { type: 'boolean' },
allowNullableObject: { type: 'boolean' },
allowNullableBoolean: { type: 'boolean' },
allowNullableString: { type: 'boolean' },
allowNullableNumber: { type: 'boolean' },
allowAny: { type: 'boolean' },
allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: {
type: 'boolean',
},
},
additionalProperties: false,
},
],
messages: {
conditionErrorOther:
'Unexpected value in conditional. ' +
'A boolean expression is required.',
conditionErrorAny:
'Unexpected any value in conditional. ' +
'An explicit comparison or type cast is required.',
conditionErrorNullish:
'Unexpected nullish value in conditional. ' +
'The condition is always false.',
conditionErrorNullableBoolean:
'Unexpected nullable boolean value in conditional. ' +
'Please handle the nullish case explicitly.',
conditionErrorString:
'Unexpected string value in conditional. ' +
'An explicit empty string check is required.',
conditionErrorNullableString:
'Unexpected nullable string value in conditional. ' +
'Please handle the nullish/empty cases explicitly.',
conditionErrorNumber:
'Unexpected number value in conditional. ' +
'An explicit zero/NaN check is required.',
conditionErrorNullableNumber:
'Unexpected nullable number value in conditional. ' +
'Please handle the nullish/zero/NaN cases explicitly.',
conditionErrorObject:
'Unexpected object value in conditional. ' +
'The condition is always true.',
conditionErrorNullableObject:
'Unexpected nullable object value in conditional. ' +
'An explicit null check is required.',
noStrictNullCheck:
'This rule requires the `strictNullChecks` compiler option to be turned on to function correctly.',
},
},
defaultOptions: [
{
allowString: true,
allowNumber: true,
allowNullableObject: true,
allowNullableBoolean: false,
allowNullableString: false,
allowNullableNumber: false,
allowAny: false,
allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing: false,
},
],
create(context, [options]) {
const service = util.getParserServices(context);
const checker = service.program.getTypeChecker();
const compilerOptions = service.program.getCompilerOptions();
const isStrictNullChecks = tsutils.isStrictCompilerOptionEnabled(
compilerOptions,
'strictNullChecks',
);
if (
!isStrictNullChecks &&
options.allowRuleToRunWithoutStrictNullChecksIKnowWhatIAmDoing !== true
) {
context.report({
loc: {
start: { line: 0, column: 0 },
end: { line: 0, column: 0 },
},
messageId: 'noStrictNullCheck',
});
}
const checkedNodes = new Set<TSESTree.Node>();
return {
ConditionalExpression: checkTestExpression,
DoWhileStatement: checkTestExpression,
ForStatement: checkTestExpression,
IfStatement: checkTestExpression,
WhileStatement: checkTestExpression,
'LogicalExpression[operator!="??"]': checkNode,
'UnaryExpression[operator="!"]': checkUnaryLogicalExpression,
};
type TestExpression =
| TSESTree.ConditionalExpression
| TSESTree.DoWhileStatement
| TSESTree.ForStatement
| TSESTree.IfStatement
| TSESTree.WhileStatement;
function checkTestExpression(node: TestExpression): void {
if (node.test == null) {
return;
}
checkNode(node.test, true);
}
function checkUnaryLogicalExpression(node: TSESTree.UnaryExpression): void {
checkNode(node.argument, true);
}
/**
* This function analyzes the type of a node and checks if it is allowed in a boolean context.
* It can recurse when checking nested logical operators, so that only the outermost operands are reported.
* The right operand of a logical expression is ignored unless it's a part of a test expression (if/while/ternary/etc).
* @param node The AST node to check.
* @param isTestExpr Whether the node is a descendant of a test expression.
*/
function checkNode(node: TSESTree.Node, isTestExpr = false): void {
// prevent checking the same node multiple times
if (checkedNodes.has(node)) {
return;
}
checkedNodes.add(node);
// for logical operator, we check its operands
if (
node.type === AST_NODE_TYPES.LogicalExpression &&
node.operator !== '??'
) {
checkNode(node.left, isTestExpr);
// we ignore the right operand when not in a context of a test expression
if (isTestExpr) {
checkNode(node.right, isTestExpr);
}
return;
}
const tsNode = service.esTreeNodeToTSNodeMap.get(node);
const type = util.getConstrainedTypeAtLocation(checker, tsNode);
const types = inspectVariantTypes(tsutils.unionTypeParts(type));
const is = (...wantedTypes: readonly VariantType[]): boolean =>
types.size === wantedTypes.length &&
wantedTypes.every(type => types.has(type));
// boolean
if (is('boolean')) {
// boolean is always okay
return;
}
// never
if (is('never')) {
// never is always okay
return;
}
// nullish
if (is('nullish')) {
// condition is always false
context.report({ node, messageId: 'conditionErrorNullish' });
return;
}
// nullable boolean
if (is('nullish', 'boolean')) {
if (!options.allowNullableBoolean) {
context.report({ node, messageId: 'conditionErrorNullableBoolean' });
}
return;
}
// string
if (is('string')) {
if (!options.allowString) {
context.report({ node, messageId: 'conditionErrorString' });
}
return;
}
// nullable string
if (is('nullish', 'string')) {
if (!options.allowNullableString) {
context.report({ node, messageId: 'conditionErrorNullableString' });
}
return;
}
// number
if (is('number')) {
if (!options.allowNumber) {
context.report({ node, messageId: 'conditionErrorNumber' });
}
return;
}
// nullable number
if (is('nullish', 'number')) {
if (!options.allowNullableNumber) {
context.report({ node, messageId: 'conditionErrorNullableNumber' });
}
return;
}
// object
if (is('object')) {
// condition is always true
context.report({ node, messageId: 'conditionErrorObject' });
return;
}
// nullable object
if (is('nullish', 'object')) {
if (!options.allowNullableObject) {
context.report({ node, messageId: 'conditionErrorNullableObject' });
}
return;
}
// any
if (is('any')) {
if (!options.allowAny) {
context.report({ node, messageId: 'conditionErrorAny' });
}
return;
}
// other
context.report({ node, messageId: 'conditionErrorOther' });
}
/** The types we care about */
type VariantType =
| 'nullish'
| 'boolean'
| 'string'
| 'number'
| 'object'
| 'any'
| 'never';
/**
* Check union variants for the types we care about
*/
function inspectVariantTypes(types: ts.Type[]): Set<VariantType> {
const variantTypes = new Set<VariantType>();
if (
types.some(type =>
tsutils.isTypeFlagSet(
type,
ts.TypeFlags.Null | ts.TypeFlags.Undefined | ts.TypeFlags.VoidLike,
),
)
) {
variantTypes.add('nullish');
}
if (
types.some(type =>
tsutils.isTypeFlagSet(type, ts.TypeFlags.BooleanLike),
)
) {
variantTypes.add('boolean');
}
if (
types.some(type => tsutils.isTypeFlagSet(type, ts.TypeFlags.StringLike))
) {
variantTypes.add('string');
}
if (
types.some(type =>
tsutils.isTypeFlagSet(
type,
ts.TypeFlags.NumberLike | ts.TypeFlags.BigIntLike,
),
)
) {
variantTypes.add('number');
}
if (
types.some(
type =>
!tsutils.isTypeFlagSet(
type,
ts.TypeFlags.Null |
ts.TypeFlags.Undefined |
ts.TypeFlags.VoidLike |
ts.TypeFlags.BooleanLike |
ts.TypeFlags.StringLike |
ts.TypeFlags.NumberLike |
ts.TypeFlags.BigIntLike |
ts.TypeFlags.Any |
ts.TypeFlags.Unknown |
ts.TypeFlags.Never,
),
)
) {
variantTypes.add('object');
}
if (
types.some(
type => util.isTypeAnyType(type) || util.isTypeUnknownType(type),
)
) {
variantTypes.add('any');
}
if (types.some(type => tsutils.isTypeFlagSet(type, ts.TypeFlags.Never))) {
variantTypes.add('never');
}
return variantTypes;
}
},
});