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explicit-function-return-type.ts
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explicit-function-return-type.ts
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import type { TSESTree } from '@typescript-eslint/utils';
import { AST_NODE_TYPES } from '@typescript-eslint/utils';
import * as util from '../util';
import {
ancestorHasReturnType,
checkFunctionReturnType,
isValidFunctionExpressionReturnType,
} from '../util/explicitReturnTypeUtils';
type Options = [
{
allowExpressions?: boolean;
allowTypedFunctionExpressions?: boolean;
allowHigherOrderFunctions?: boolean;
allowDirectConstAssertionInArrowFunctions?: boolean;
allowConciseArrowFunctionExpressionsStartingWithVoid?: boolean;
allowFunctionsWithoutTypeParameters?: boolean;
allowedNames?: string[];
allowIIFEs?: boolean;
},
];
type MessageIds = 'missingReturnType';
export default util.createRule<Options, MessageIds>({
name: 'explicit-function-return-type',
meta: {
type: 'problem',
docs: {
description:
'Require explicit return types on functions and class methods',
recommended: false,
},
messages: {
missingReturnType: 'Missing return type on function.',
},
schema: [
{
type: 'object',
properties: {
allowConciseArrowFunctionExpressionsStartingWithVoid: {
description:
'Whether to allow arrow functions that start with the `void` keyword.',
type: 'boolean',
},
allowExpressions: {
description:
'Whether to ignore function expressions (functions which are not part of a declaration).',
type: 'boolean',
},
allowHigherOrderFunctions: {
description:
'Whether to ignore functions immediately returning another function expression.',
type: 'boolean',
},
allowTypedFunctionExpressions: {
description:
'Whether to ignore type annotations on the variable of function expressions.',
type: 'boolean',
},
allowDirectConstAssertionInArrowFunctions: {
description:
'Whether to ignore arrow functions immediately returning a `as const` value.',
type: 'boolean',
},
allowFunctionsWithoutTypeParameters: {
description:
"Whether to ignore functions that don't have generic type parameters.",
type: 'boolean',
},
allowedNames: {
description:
'An array of function/method names that will not have their arguments or return values checked.',
items: {
type: 'string',
},
type: 'array',
},
allowIIFEs: {
description:
'Whether to ignore immediately invoked function expressions (IIFEs).',
type: 'boolean',
},
},
additionalProperties: false,
},
],
},
defaultOptions: [
{
allowExpressions: false,
allowTypedFunctionExpressions: true,
allowHigherOrderFunctions: true,
allowDirectConstAssertionInArrowFunctions: true,
allowConciseArrowFunctionExpressionsStartingWithVoid: false,
allowedNames: [],
allowIIFEs: false,
},
],
create(context, [options]) {
const sourceCode = context.getSourceCode();
function isAllowedFunction(
node:
| TSESTree.ArrowFunctionExpression
| TSESTree.FunctionExpression
| TSESTree.FunctionDeclaration,
): boolean {
if (options.allowFunctionsWithoutTypeParameters && !node.typeParameters) {
return true;
}
if (options.allowIIFEs && isIIFE(node)) {
return true;
}
if (!options.allowedNames?.length) {
return false;
}
if (
node.type === AST_NODE_TYPES.ArrowFunctionExpression ||
node.type === AST_NODE_TYPES.FunctionExpression
) {
const parent = node.parent;
let funcName;
if (node.id?.name) {
funcName = node.id.name;
} else if (parent) {
switch (parent.type) {
case AST_NODE_TYPES.VariableDeclarator: {
if (parent.id.type === AST_NODE_TYPES.Identifier) {
funcName = parent.id.name;
}
break;
}
case AST_NODE_TYPES.MethodDefinition:
case AST_NODE_TYPES.PropertyDefinition:
case AST_NODE_TYPES.Property: {
if (
parent.key.type === AST_NODE_TYPES.Identifier &&
parent.computed === false
) {
funcName = parent.key.name;
}
break;
}
}
}
if (!!funcName && !!options.allowedNames.includes(funcName)) {
return true;
}
}
if (
node.type === AST_NODE_TYPES.FunctionDeclaration &&
node.id &&
node.id.type === AST_NODE_TYPES.Identifier &&
!!options.allowedNames.includes(node.id.name)
) {
return true;
}
return false;
}
function isIIFE(
node:
| TSESTree.ArrowFunctionExpression
| TSESTree.FunctionExpression
| TSESTree.FunctionDeclaration,
): boolean {
return node.parent.type === AST_NODE_TYPES.CallExpression;
}
return {
'ArrowFunctionExpression, FunctionExpression'(
node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionExpression,
): void {
if (
options.allowConciseArrowFunctionExpressionsStartingWithVoid &&
node.type === AST_NODE_TYPES.ArrowFunctionExpression &&
node.expression &&
node.body.type === AST_NODE_TYPES.UnaryExpression &&
node.body.operator === 'void'
) {
return;
}
if (isAllowedFunction(node)) {
return;
}
if (
options.allowTypedFunctionExpressions &&
(isValidFunctionExpressionReturnType(node, options) ||
ancestorHasReturnType(node))
) {
return;
}
checkFunctionReturnType(node, options, sourceCode, loc =>
context.report({
node,
loc,
messageId: 'missingReturnType',
}),
);
},
FunctionDeclaration(node): void {
if (isAllowedFunction(node)) {
return;
}
if (options.allowTypedFunctionExpressions && node.returnType) {
return;
}
checkFunctionReturnType(node, options, sourceCode, loc =>
context.report({
node,
loc,
messageId: 'missingReturnType',
}),
);
},
};
},
});