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returnUndefinedRule.ts
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returnUndefinedRule.ts
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/**
* @license
* Copyright 2017 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 {
hasModifier,
isIdentifier,
isReturnStatement,
isTypeFlagSet,
isTypeReference,
isUnionType,
} from "tsutils";
import * as ts from "typescript";
import * as Lint from "../index";
export class Rule extends Lint.Rules.TypedRule {
/* tslint:disable:object-literal-sort-keys */
public static metadata: Lint.IRuleMetadata = {
ruleName: "return-undefined",
description:
"Prefer `return;` in void functions and `return undefined;` in value-returning functions.",
optionsDescription: "Not configurable.",
options: null,
optionExamples: [true],
type: "style",
typescriptOnly: false,
requiresTypeInfo: true,
};
/* tslint:enable:object-literal-sort-keys */
public static FAILURE_STRING_VALUE_RETURN =
"Value-returning function should use `return undefined;`, not just `return;`.";
public static FAILURE_STRING_VOID_RETURN =
"`void` function should use `return;`, not `return undefined;`.";
public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
return this.applyWithFunction(sourceFile, walk, undefined, program.getTypeChecker());
}
}
function walk(ctx: Lint.WalkContext, checker: ts.TypeChecker) {
return ts.forEachChild(ctx.sourceFile, function cb(node: ts.Node): void {
if (isReturnStatement(node)) {
check(node);
}
return ts.forEachChild(node, cb);
});
function check(node: ts.ReturnStatement): void {
const actualReturnKind = getReturnKindFromReturnStatement(node);
if (actualReturnKind === undefined) {
return;
}
const functionReturningFrom = Lint.ancestorWhere(node, isFunctionLike);
if (functionReturningFrom === undefined) {
// Return outside of function is invalid
return;
}
const returnKindFromType = getReturnKindFromFunction(functionReturningFrom, checker);
if (returnKindFromType !== undefined && returnKindFromType !== actualReturnKind) {
ctx.addFailureAtNode(
node,
returnKindFromType === ReturnKind.Void
? Rule.FAILURE_STRING_VOID_RETURN
: Rule.FAILURE_STRING_VALUE_RETURN,
);
}
}
}
function getReturnKindFromReturnStatement(node: ts.ReturnStatement): ReturnKind | undefined {
if (node.expression === undefined) {
return ReturnKind.Void;
} else if (isIdentifier(node.expression) && node.expression.text === "undefined") {
return ReturnKind.Value;
} else {
return undefined;
}
}
const enum ReturnKind {
Void = "void",
Value = "value",
}
type FunctionLike =
| ts.FunctionDeclaration
| ts.FunctionExpression
| ts.ArrowFunction
| ts.MethodDeclaration
| ts.ConstructorDeclaration
| ts.GetAccessorDeclaration
| ts.SetAccessorDeclaration;
function getReturnKindFromFunction(
node: FunctionLike,
checker: ts.TypeChecker,
): ReturnKind | undefined {
switch (node.kind) {
case ts.SyntaxKind.Constructor:
case ts.SyntaxKind.SetAccessor:
return ReturnKind.Void;
case ts.SyntaxKind.GetAccessor:
return ReturnKind.Value;
}
// Handle generator functions/methods:
if (node.asteriskToken !== undefined) {
return ReturnKind.Void;
}
const contextual =
isFunctionExpressionLike(node) && node.type === undefined
? tryGetReturnType(checker.getContextualType(node), checker)
: undefined;
const returnType =
contextual !== undefined
? contextual
: tryGetReturnType(checker.getTypeAtLocation(node), checker);
if (returnType === undefined || isTypeFlagSet(returnType, ts.TypeFlags.Any)) {
return undefined;
}
const effectivelyVoidChecker = hasModifier(node.modifiers, ts.SyntaxKind.AsyncKeyword)
? isEffectivelyVoidPromise
: isEffectivelyVoid;
if (effectivelyVoidChecker(returnType)) {
return ReturnKind.Void;
}
return ReturnKind.Value;
}
/** True for `void`, `undefined`, Promise<void>, or `void | undefined | Promise<void>`. */
function isEffectivelyVoidPromise(type: ts.Type): boolean {
// Would need access to `checker.getPromisedTypeOfPromise` to do this properly.
// Assume that the return type is the global Promise (since this is an async function) and get its type argument.
return (
// tslint:disable-next-line:no-bitwise
isTypeFlagSet(type, ts.TypeFlags.Void | ts.TypeFlags.Undefined) ||
(isUnionType(type) && type.types.every(isEffectivelyVoidPromise)) ||
(isTypeReference(type) &&
type.typeArguments !== undefined &&
type.typeArguments.length === 1 &&
isEffectivelyVoidPromise(type.typeArguments[0]))
);
}
/** True for `void`, `undefined`, or `void | undefined`. */
function isEffectivelyVoid(type: ts.Type): boolean {
return (
// tslint:disable-next-line:no-bitwise
isTypeFlagSet(type, ts.TypeFlags.Void | ts.TypeFlags.Undefined) ||
(isUnionType(type) && type.types.every(isEffectivelyVoid))
);
}
function tryGetReturnType(
fnType: ts.Type | undefined,
checker: ts.TypeChecker,
): ts.Type | undefined {
if (fnType === undefined) {
return undefined;
}
const sigs = checker.getSignaturesOfType(fnType, ts.SignatureKind.Call);
if (sigs.length !== 1) {
return undefined;
}
return checker.getReturnTypeOfSignature(sigs[0]);
}
function isFunctionLike(node: ts.Node): node is FunctionLike {
switch (node.kind) {
case ts.SyntaxKind.FunctionDeclaration:
case ts.SyntaxKind.FunctionExpression:
case ts.SyntaxKind.ArrowFunction:
case ts.SyntaxKind.MethodDeclaration:
case ts.SyntaxKind.Constructor:
case ts.SyntaxKind.GetAccessor:
case ts.SyntaxKind.SetAccessor:
return true;
default:
return false;
}
}
function isFunctionExpressionLike(node: ts.Node): node is ts.FunctionExpression | ts.ArrowFunction {
return (
node.kind === ts.SyntaxKind.FunctionExpression || node.kind === ts.SyntaxKind.ArrowFunction
);
}