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strictBooleanExpressionsRule.ts
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strictBooleanExpressionsRule.ts
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/**
* @license
* Copyright 2016 Palantir Technologies, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import * as ts from "typescript";
import * as Lint from "../index";
const OPTION_ALLOW_NULL_UNION = "allow-null-union";
const OPTION_ALLOW_UNDEFINED_UNION = "allow-undefined-union";
const OPTION_ALLOW_STRING = "allow-string";
const OPTION_ALLOW_NUMBER = "allow-number";
const OPTION_ALLOW_MIX = "allow-mix";
// tslint:disable object-literal-sort-keys switch-default
export class Rule extends Lint.Rules.TypedRule {
public static metadata: Lint.IRuleMetadata = {
ruleName: "strict-boolean-expressions",
description: Lint.Utils.dedent`
Restricts the types allowed in boolean expressions. By default only booleans are allowed.
The following nodes are checked:
* Arguments to the \`!\`, \`&&\`, and \`||\` operators
* The condition in a conditional expression (\`cond ? x : y\`)
* Conditions for \`if\`, \`for\`, \`while\`, and \`do-while\` statements.`,
optionsDescription: Lint.Utils.dedent`
These options may be provided:
* \`${OPTION_ALLOW_NULL_UNION}\` allows union types containing \`null\`.
- It does *not* allow \`null\` itself.
- Without the '--strictNullChecks' compiler option, this will allow anything other than a string, number, or enum.
* \`${OPTION_ALLOW_UNDEFINED_UNION}\` allows union types containing \`undefined\`.
- It does *not* allow \`undefined\` itself.
- Without the '--strictNullChecks' compiler option, this will allow anything other than a string, number, or enum.
* \`${OPTION_ALLOW_STRING}\` allows strings.
- It does *not* allow unions containing \`string\`.
- It does *not* allow string literal types.
* \`${OPTION_ALLOW_NUMBER}\` allows numbers.
- It does *not* allow unions containing \`number\`.
- It does *not* allow enums or number literal types.
* \`${OPTION_ALLOW_MIX}\` allow multiple of the above to appear together.
- For example, \`string | number\` or \`RegExp | null | undefined\` would normally not be allowed.
- A type like \`"foo" | "bar" | undefined\` is always allowed, because it has only one way to be false.`,
options: {
type: "array",
items: {
type: "string",
enum: [OPTION_ALLOW_NULL_UNION, OPTION_ALLOW_UNDEFINED_UNION, OPTION_ALLOW_STRING, OPTION_ALLOW_NUMBER],
},
minLength: 0,
maxLength: 5,
},
optionExamples: [
true,
[true, OPTION_ALLOW_NULL_UNION, OPTION_ALLOW_UNDEFINED_UNION, OPTION_ALLOW_STRING, OPTION_ALLOW_NUMBER],
],
type: "functionality",
typescriptOnly: true,
requiresTypeInfo: true,
};
public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
const options = parseOptions(this.ruleArguments, Lint.isStrictNullChecksEnabled(program.getCompilerOptions()));
return this.applyWithFunction(sourceFile, (ctx: Lint.WalkContext<Options>) => walk(ctx, program.getTypeChecker()), options);
}
}
interface Options {
strictNullChecks: boolean;
allowNullUnion: boolean;
allowUndefinedUnion: boolean;
allowString: boolean;
allowNumber: boolean;
allowMix: boolean;
}
function parseOptions(ruleArguments: string[], strictNullChecks: boolean): Options {
return {
strictNullChecks,
allowNullUnion: has(OPTION_ALLOW_NULL_UNION),
allowUndefinedUnion: has(OPTION_ALLOW_UNDEFINED_UNION),
allowString: has(OPTION_ALLOW_STRING),
allowNumber: has(OPTION_ALLOW_NUMBER),
allowMix: has(OPTION_ALLOW_MIX),
};
function has(name: string): boolean {
return ruleArguments.indexOf(name) !== -1;
}
}
function walk(ctx: Lint.WalkContext<Options>, checker: ts.TypeChecker): void {
const { sourceFile, options } = ctx;
ts.forEachChild(sourceFile, function cb(node: ts.Node): void {
switch (node.kind) {
case ts.SyntaxKind.BinaryExpression: {
const b = node as ts.BinaryExpression;
if (binaryBooleanExpressionKind(b) !== undefined) {
const { left, right } = b;
const checkHalf = (expr: ts.Expression) => {
// If it's another boolean binary expression, we'll check it when recursing.
if (!isBooleanBinaryExpression(expr)) {
checkExpression(expr, b);
}
};
checkHalf(left);
checkHalf(right);
}
break;
}
case ts.SyntaxKind.PrefixUnaryExpression: {
const { operator, operand } = node as ts.PrefixUnaryExpression;
if (operator === ts.SyntaxKind.ExclamationToken) {
checkExpression(operand, node as ts.PrefixUnaryExpression);
}
break;
}
case ts.SyntaxKind.IfStatement:
case ts.SyntaxKind.WhileStatement:
case ts.SyntaxKind.DoStatement: {
const c = node as ts.IfStatement | ts.WhileStatement | ts.DoStatement;
// If it's a boolean binary expression, we'll check it when recursing.
if (!isBooleanBinaryExpression(c.expression)) {
checkExpression(c.expression, c);
}
break;
}
case ts.SyntaxKind.ConditionalExpression:
checkExpression((node as ts.ConditionalExpression).condition, node as ts.ConditionalExpression);
break;
case ts.SyntaxKind.ForStatement: {
const { condition } = node as ts.ForStatement;
if (condition !== undefined) {
checkExpression(condition, node as ts.ForStatement);
}
break;
}
}
return ts.forEachChild(node, cb);
});
function checkExpression(node: ts.Expression, location: Location): void {
const type = checker.getTypeAtLocation(node);
const failure = getTypeFailure(type, options);
if (failure !== undefined) {
if (failure === TypeFailure.AlwaysTruthy &&
!options.strictNullChecks &&
(options.allowNullUnion || options.allowUndefinedUnion)) {
// OK; It might be null/undefined.
return;
}
ctx.addFailureAtNode(node,
showFailure(location, failure, isUnionType(type), options));
}
}
}
function getTypeFailure(type: ts.Type, options: Options): TypeFailure | undefined {
if (isUnionType(type)) {
return handleUnion(type, options);
}
const kind = getKind(type);
const failure = failureForKind(kind, /*isInUnion*/false, options);
if (failure !== undefined) {
return failure;
}
switch (triState(kind)) {
case true:
return TypeFailure.AlwaysTruthy;
case false:
return TypeFailure.AlwaysFalsy;
case undefined:
return undefined;
}
}
function handleUnion(type: ts.UnionType, options: Options): TypeFailure | undefined {
// Tracks whether it's possibly truthy.
let anyTruthy = false;
// Counts falsy kinds to see if there's a mix. Also tracks whether it's possibly falsy.
let seenFalsy = 0;
for (const ty of type.types) {
const kind = getKind(ty);
const failure = failureForKind(kind, /*isInUnion*/true, options);
if (failure !== undefined) {
return failure;
}
switch (triState(kind)) {
case true:
anyTruthy = true;
break;
case false:
seenFalsy++;
break;
default:
anyTruthy = true;
seenFalsy++;
}
}
return seenFalsy === 0 ? TypeFailure.AlwaysTruthy
: !anyTruthy ? TypeFailure.AlwaysFalsy
: !options.allowMix && seenFalsy > 1 ? TypeFailure.Mixes : undefined;
}
/** Fails if a kind of falsiness is not allowed. */
function failureForKind(kind: TypeKind, isInUnion: boolean, options: Options): TypeFailure | undefined {
switch (kind) {
case TypeKind.String:
case TypeKind.FalseStringLiteral:
return options.allowString ? undefined : TypeFailure.String;
case TypeKind.Number:
case TypeKind.FalseNumberLiteral:
return options.allowNumber ? undefined : TypeFailure.Number;
case TypeKind.Enum:
return TypeFailure.Enum;
case TypeKind.Null:
return isInUnion && !options.allowNullUnion ? TypeFailure.Null : undefined;
case TypeKind.Undefined:
return isInUnion && !options.allowUndefinedUnion ? TypeFailure.Undefined : undefined;
default:
return undefined;
}
}
export type Location =
| ts.PrefixUnaryExpression
| ts.IfStatement
| ts.WhileStatement
| ts.DoStatement
| ts.ForStatement
| ts.ConditionalExpression
| ts.BinaryExpression;
export const enum TypeFailure {
AlwaysTruthy,
AlwaysFalsy,
String,
Number,
Null,
Undefined,
Enum,
Mixes,
}
const enum TypeKind {
String,
FalseStringLiteral,
Number,
FalseNumberLiteral,
Boolean,
FalseBooleanLiteral,
Null,
Undefined,
Enum,
AlwaysTruthy,
}
/** Divides a type into always true, always false, or unknown. */
function triState(kind: TypeKind): boolean | undefined {
switch (kind) {
case TypeKind.String:
case TypeKind.Number:
case TypeKind.Boolean:
case TypeKind.Enum:
return undefined;
case TypeKind.Null:
case TypeKind.Undefined:
case TypeKind.FalseNumberLiteral:
case TypeKind.FalseStringLiteral:
case TypeKind.FalseBooleanLiteral:
return false;
case TypeKind.AlwaysTruthy:
return true;
}
}
function getKind(type: ts.Type): TypeKind {
return is(ts.TypeFlags.String) ? TypeKind.String
: is(ts.TypeFlags.Number) ? TypeKind.Number
: is(ts.TypeFlags.Boolean) ? TypeKind.Boolean
: is(ts.TypeFlags.Null) ? TypeKind.Null
: is(ts.TypeFlags.Undefined | ts.TypeFlags.Void) ? TypeKind.Undefined // tslint:disable-line:no-bitwise
: is(ts.TypeFlags.EnumLike) ? TypeKind.Enum
: is(ts.TypeFlags.NumberLiteral) ?
(numberLiteralIsZero(type as ts.LiteralType) ? TypeKind.FalseNumberLiteral : TypeKind.AlwaysTruthy)
: is(ts.TypeFlags.StringLiteral) ?
(stringLiteralIsEmpty(type as ts.LiteralType) ? TypeKind.FalseStringLiteral : TypeKind.AlwaysTruthy)
: is(ts.TypeFlags.BooleanLiteral) ?
((type as ts.IntrinsicType).intrinsicName === "true" ? TypeKind.AlwaysTruthy : TypeKind.FalseBooleanLiteral)
: TypeKind.AlwaysTruthy;
function is(flags: ts.TypeFlags) {
return Lint.isTypeFlagSet(type, flags);
}
}
function numberLiteralIsZero(type: ts.LiteralType): boolean {
// Uses 'value' in TypeScript>=2.4.
return (type as any).value !== undefined ? (type as any).value === 0 : type.text === "0";
}
function stringLiteralIsEmpty(type: ts.LiteralType): boolean {
return ((type as any).value !== undefined ? (type as any).value : type.text) === "";
}
/** Matches `&&` and `||` operators. */
function isBooleanBinaryExpression(node: ts.Expression): boolean {
return node.kind === ts.SyntaxKind.BinaryExpression && binaryBooleanExpressionKind(node as ts.BinaryExpression) !== undefined;
}
function binaryBooleanExpressionKind(node: ts.BinaryExpression): "&&" | "||" | undefined {
switch (node.operatorToken.kind) {
case ts.SyntaxKind.AmpersandAmpersandToken:
return "&&";
case ts.SyntaxKind.BarBarToken:
return "||";
default:
return undefined;
}
}
function stringOr(parts: string[]): string {
switch (parts.length) {
case 1:
return parts[0];
case 2:
return `${parts[0]} or ${parts[1]}`;
default:
let res = "";
for (let i = 0; i < parts.length - 1; i++) {
res += `${parts[i]}, `;
}
return `${res}or ${parts[parts.length - 1]}`;
}
}
function isUnionType(type: ts.Type): type is ts.UnionType {
return Lint.isTypeFlagSet(type, ts.TypeFlags.Union) && !Lint.isTypeFlagSet(type, ts.TypeFlags.Enum);
}
function showLocation(n: Location): string {
switch (n.kind) {
case ts.SyntaxKind.PrefixUnaryExpression:
return "operand for the '!' operator";
case ts.SyntaxKind.ConditionalExpression:
return "condition";
case ts.SyntaxKind.ForStatement:
return "'for' condition";
case ts.SyntaxKind.IfStatement:
return "'if' condition";
case ts.SyntaxKind.WhileStatement:
return "'while' condition";
case ts.SyntaxKind.DoStatement:
return "'do-while' condition";
case ts.SyntaxKind.BinaryExpression:
return `operand for the '${binaryBooleanExpressionKind(n as ts.BinaryExpression)}' operator`;
}
}
function showFailure(location: Location, ty: TypeFailure, isUnionType: boolean, options: Options): string {
const expectedTypes = showExpectedTypes(options);
const expected = expectedTypes.length === 1
? `Only ${expectedTypes[0]}s are allowed`
: `Allowed types are ${stringOr(expectedTypes)}`;
const tyFail = showTypeFailure(ty, isUnionType, options.strictNullChecks);
return `This type is not allowed in the ${showLocation(location)} because it ${tyFail}. ${expected}.`;
}
function showExpectedTypes(options: Options): string[] {
const parts = ["boolean"];
if (options.allowNullUnion) { parts.push("null-union"); }
if (options.allowUndefinedUnion) { parts.push("undefined-union"); }
if (options.allowString) { parts.push("string"); }
if (options.allowNumber) { parts.push("number"); }
return parts;
}
function showTypeFailure(ty: TypeFailure, isUnionType: boolean, strictNullChecks: boolean) {
const is = isUnionType ? "could be" : "is";
switch (ty) {
case TypeFailure.AlwaysTruthy:
return strictNullChecks
? "is always truthy"
: "is always truthy. It may be null/undefined, but neither " +
`'${OPTION_ALLOW_NULL_UNION}' nor '${OPTION_ALLOW_UNDEFINED_UNION}' is set`;
case TypeFailure.AlwaysFalsy: return "is always falsy";
case TypeFailure.String: return `${is} a string`;
case TypeFailure.Number: return `${is} a number`;
case TypeFailure.Null: return `${is} null`;
case TypeFailure.Undefined: return `${is} undefined`;
case TypeFailure.Enum: return `${is} an enum`;
case TypeFailure.Mixes: return "unions more than one truthy/falsy type";
}
}
declare module "typescript" {
// No other way to distinguish boolean literal true from boolean literal false
export interface IntrinsicType extends ts.Type {
intrinsicName: string;
}
}