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restrict-plus-operands.ts
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restrict-plus-operands.ts
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import { TSESTree } from '@typescript-eslint/experimental-utils';
import * as ts from 'typescript';
import * as util from '../util';
type Options = [
{
checkCompoundAssignments?: boolean;
allowAny?: boolean;
},
];
type MessageIds = 'notNumbers' | 'notStrings' | 'notBigInts';
export default util.createRule<Options, MessageIds>({
name: 'restrict-plus-operands',
meta: {
type: 'problem',
docs: {
description:
'When adding two variables, operands must both be of type number or of type string',
recommended: 'error',
requiresTypeChecking: true,
},
messages: {
notNumbers:
"Operands of '+' operation must either be both strings or both numbers.",
notStrings:
"Operands of '+' operation must either be both strings or both numbers. Consider using a template literal.",
notBigInts: "Operands of '+' operation must be both bigints.",
},
schema: [
{
type: 'object',
additionalProperties: false,
properties: {
checkCompoundAssignments: {
type: 'boolean',
},
allowAny: {
type: 'boolean',
},
},
},
],
},
defaultOptions: [
{
checkCompoundAssignments: false,
allowAny: false,
},
],
create(context, [{ checkCompoundAssignments, allowAny }]) {
const service = util.getParserServices(context);
const typeChecker = service.program.getTypeChecker();
type BaseLiteral = 'string' | 'number' | 'bigint' | 'invalid' | 'any';
/**
* Helper function to get base type of node
*/
function getBaseTypeOfLiteralType(type: ts.Type): BaseLiteral {
if (type.isNumberLiteral()) {
return 'number';
}
if (
type.isStringLiteral() ||
util.isTypeFlagSet(type, ts.TypeFlags.TemplateLiteral)
) {
return 'string';
}
// is BigIntLiteral
if (type.flags & ts.TypeFlags.BigIntLiteral) {
return 'bigint';
}
if (type.isUnion()) {
const types = type.types.map(getBaseTypeOfLiteralType);
return types.every(value => value === types[0]) ? types[0] : 'invalid';
}
if (type.isIntersection()) {
const types = type.types.map(getBaseTypeOfLiteralType);
return types.some(value => value === 'string') ? 'string' : 'invalid';
}
const stringType = typeChecker.typeToString(type);
if (
stringType === 'number' ||
stringType === 'string' ||
stringType === 'bigint' ||
stringType === 'any'
) {
return stringType;
}
return 'invalid';
}
/**
* Helper function to get base type of node
* @param node the node to be evaluated.
*/
function getNodeType(
node: TSESTree.Expression | TSESTree.PrivateIdentifier,
): BaseLiteral {
const tsNode = service.esTreeNodeToTSNodeMap.get(node);
const type = util.getConstrainedTypeAtLocation(typeChecker, tsNode);
return getBaseTypeOfLiteralType(type);
}
function checkPlusOperands(
node: TSESTree.BinaryExpression | TSESTree.AssignmentExpression,
): void {
const leftType = getNodeType(node.left);
const rightType = getNodeType(node.right);
if (leftType === rightType) {
if (leftType === 'invalid') {
context.report({
node,
messageId: 'notNumbers',
});
}
if (!allowAny && leftType === 'any') {
context.report({
node,
messageId: 'notNumbers',
});
}
return;
}
if (leftType === 'any' || rightType === 'any') {
if (!allowAny || leftType === 'invalid' || rightType === 'invalid') {
context.report({
node,
messageId: 'notNumbers',
});
}
return;
}
if (leftType === 'string' || rightType === 'string') {
return context.report({
node,
messageId: 'notStrings',
});
}
if (leftType === 'bigint' || rightType === 'bigint') {
return context.report({
node,
messageId: 'notBigInts',
});
}
context.report({
node,
messageId: 'notNumbers',
});
}
return {
"BinaryExpression[operator='+']": checkPlusOperands,
...(checkCompoundAssignments && {
"AssignmentExpression[operator='+=']"(node): void {
checkPlusOperands(node);
},
}),
};
},
});