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explicit-function-return-type.ts
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explicit-function-return-type.ts
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import { TSESTree, AST_NODE_TYPES } from '@typescript-eslint/typescript-estree';
import * as util from '../util';
type Options = [
{
allowExpressions?: boolean;
allowTypedFunctionExpressions?: 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',
category: 'Stylistic Issues',
recommended: 'warn',
},
messages: {
missingReturnType: 'Missing return type on function.',
},
schema: [
{
type: 'object',
properties: {
allowExpressions: {
type: 'boolean',
},
allowTypedFunctionExpressions: {
type: 'boolean',
},
},
additionalProperties: false,
},
],
},
defaultOptions: [
{
allowExpressions: true,
allowTypedFunctionExpressions: false,
},
],
create(context, [options]) {
/**
* Checks if the parent of a function expression is a constructor.
* @param parent The parent of a function expression node
*/
function isConstructor(parent: TSESTree.Node): boolean {
return (
parent.type === AST_NODE_TYPES.MethodDefinition &&
parent.kind === 'constructor'
);
}
/**
* Checks if the parent of a function expression is a setter.
* @param parent The parent of a function expression node
*/
function isSetter(parent: TSESTree.Node): boolean {
return (
parent.type === AST_NODE_TYPES.MethodDefinition && parent.kind === 'set'
);
}
/**
* Checks if the parent of a function expression has a type annotation.
* @param parent The parent of a function expression node
*/
function hasTypeAnnotation(parent: TSESTree.Node): boolean {
return (
parent.type === AST_NODE_TYPES.VariableDeclarator &&
!!parent.id.typeAnnotation
);
}
/**
* Checks if a function declaration/expression has a return type.
* @param node The node representing a function.
*/
function checkFunctionReturnType(
node:
| TSESTree.ArrowFunctionExpression
| TSESTree.FunctionDeclaration
| TSESTree.FunctionExpression,
): void {
if (
!node.returnType &&
node.parent &&
!isConstructor(node.parent) &&
!isSetter(node.parent) &&
util.isTypeScriptFile(context.getFilename())
) {
context.report({
node,
messageId: 'missingReturnType',
});
}
}
/**
* Checks if a function declaration/expression has a return type.
* @param {ASTNode} node The node representing a function.
*/
function checkFunctionExpressionReturnType(
node:
| TSESTree.ArrowFunctionExpression
| TSESTree.FunctionDeclaration
| TSESTree.FunctionExpression,
): void {
if (
options.allowExpressions &&
node.parent &&
node.parent.type !== AST_NODE_TYPES.VariableDeclarator &&
node.parent.type !== AST_NODE_TYPES.MethodDefinition
) {
return;
}
if (
options.allowTypedFunctionExpressions &&
node.parent &&
hasTypeAnnotation(node.parent)
) {
return;
}
checkFunctionReturnType(node);
}
return {
ArrowFunctionExpression: checkFunctionExpressionReturnType,
FunctionDeclaration: checkFunctionReturnType,
FunctionExpression: checkFunctionExpressionReturnType,
};
},
});