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feat(eslint-plugin): add new rule no-floating-promises (#495)
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,46 @@ | ||
| # Requires Promise-like values to be handled appropriately (no-floating-promises) | ||
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| This rule forbids usage of Promise-like values in statements without handling | ||
| their errors appropriately. Unhandled promises can cause several issues, such | ||
| as improperly sequenced operations, ignored Promise rejections and more. Valid | ||
| ways of handling a Promise-valued statement include `await`ing, returning, and | ||
| either calling `.then()` with two arguments or `.catch()` with one argument. | ||
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| ## Rule Details | ||
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| Examples of **incorrect** code for this rule: | ||
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| ```ts | ||
| const promise = new Promise((resolve, reject) => resolve('value')); | ||
| promise; | ||
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| async function returnsPromise() { | ||
| return 'value'; | ||
| } | ||
| returnsPromise().then(() => {}); | ||
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| Promise.reject('value').catch(); | ||
| ``` | ||
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| Examples of **correct** code for this rule: | ||
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| ```ts | ||
| const promise = new Promise((resolve, reject) => resolve('value')); | ||
| await promise; | ||
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| async function returnsPromise() { | ||
| return 'value'; | ||
| } | ||
| returnsPromise().then(() => {}, () => {}); | ||
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| Promise.reject('value').catch(() => {}); | ||
| ``` | ||
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| ## When Not To Use It | ||
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| If you do not use Promise-like values in your codebase or want to allow them to | ||
| remain unhandled. | ||
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| ## Related to | ||
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| - Tslint: ['no-floating-promises'](https://palantir.github.io/tslint/rules/no-floating-promises/) |
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packages/eslint-plugin/src/rules/no-floating-promises.ts
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,171 @@ | ||
| import * as tsutils from 'tsutils'; | ||
| import * as ts from 'typescript'; | ||
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| import * as util from '../util'; | ||
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| export default util.createRule({ | ||
| name: 'no-floating-promises', | ||
| meta: { | ||
| docs: { | ||
| description: 'Requires Promise-like values to be handled appropriately.', | ||
| category: 'Best Practices', | ||
| recommended: false, | ||
| }, | ||
| messages: { | ||
| floating: 'Promises must be handled appropriately', | ||
| }, | ||
| schema: [], | ||
| type: 'problem', | ||
| }, | ||
| defaultOptions: [], | ||
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| create(context) { | ||
| const parserServices = util.getParserServices(context); | ||
| const checker = parserServices.program.getTypeChecker(); | ||
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| return { | ||
| ExpressionStatement(node) { | ||
| const { expression } = parserServices.esTreeNodeToTSNodeMap.get( | ||
| node, | ||
| ) as ts.ExpressionStatement; | ||
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| if (isUnhandledPromise(checker, expression)) { | ||
| context.report({ | ||
| messageId: 'floating', | ||
| node, | ||
| }); | ||
| } | ||
| }, | ||
| }; | ||
| }, | ||
| }); | ||
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| function isUnhandledPromise(checker: ts.TypeChecker, node: ts.Node): boolean { | ||
| // First, check expressions whose resulting types may not be promise-like | ||
| if ( | ||
| ts.isBinaryExpression(node) && | ||
| node.operatorToken.kind === ts.SyntaxKind.CommaToken | ||
| ) { | ||
| // Any child in a comma expression could return a potentially unhandled | ||
| // promise, so we check them all regardless of whether the final returned | ||
| // value is promise-like. | ||
| return ( | ||
| isUnhandledPromise(checker, node.left) || | ||
| isUnhandledPromise(checker, node.right) | ||
| ); | ||
| } else if (ts.isVoidExpression(node)) { | ||
| // Similarly, a `void` expression always returns undefined, so we need to | ||
| // see what's inside it without checking the type of the overall expression. | ||
| return isUnhandledPromise(checker, node.expression); | ||
| } | ||
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| // Check the type. At this point it can't be unhandled if it isn't a promise | ||
| if (!isPromiseLike(checker, node)) { | ||
| return false; | ||
| } | ||
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| if (ts.isCallExpression(node)) { | ||
| // If the outer expression is a call, it must be either a `.then()` or | ||
| // `.catch()` that handles the promise. | ||
| return ( | ||
| !isPromiseCatchCallWithHandler(node) && | ||
| !isPromiseThenCallWithRejectionHandler(node) | ||
| ); | ||
| } else if (ts.isConditionalExpression(node)) { | ||
| // We must be getting the promise-like value from one of the branches of the | ||
| // ternary. Check them directly. | ||
| return ( | ||
| isUnhandledPromise(checker, node.whenFalse) || | ||
| isUnhandledPromise(checker, node.whenTrue) | ||
| ); | ||
| } else if ( | ||
| ts.isPropertyAccessExpression(node) || | ||
| ts.isIdentifier(node) || | ||
| ts.isNewExpression(node) | ||
| ) { | ||
| // If it is just a property access chain or a `new` call (e.g. `foo.bar` or | ||
| // `new Promise()`), the promise is not handled because it doesn't have the | ||
| // necessary then/catch call at the end of the chain. | ||
| return true; | ||
| } | ||
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| // We conservatively return false for all other types of expressions because | ||
| // we don't want to accidentally fail if the promise is handled internally but | ||
| // we just can't tell. | ||
| return false; | ||
| } | ||
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| // Modified from tsutils.isThenable() to only consider thenables which can be | ||
| // rejected/caught via a second parameter. Original source (MIT licensed): | ||
| // | ||
| // https://github.com/ajafff/tsutils/blob/49d0d31050b44b81e918eae4fbaf1dfe7b7286af/util/type.ts#L95-L125 | ||
| function isPromiseLike(checker: ts.TypeChecker, node: ts.Node): boolean { | ||
| const type = checker.getTypeAtLocation(node); | ||
| for (const ty of tsutils.unionTypeParts(checker.getApparentType(type))) { | ||
| const then = ty.getProperty('then'); | ||
| if (then === undefined) { | ||
| continue; | ||
| } | ||
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| const thenType = checker.getTypeOfSymbolAtLocation(then, node); | ||
| if ( | ||
| hasMatchingSignature( | ||
| thenType, | ||
| signature => | ||
| signature.parameters.length >= 2 && | ||
| isFunctionParam(checker, signature.parameters[0], node) && | ||
| isFunctionParam(checker, signature.parameters[1], node), | ||
| ) | ||
| ) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| function hasMatchingSignature( | ||
| type: ts.Type, | ||
| matcher: (signature: ts.Signature) => boolean, | ||
| ): boolean { | ||
| for (const t of tsutils.unionTypeParts(type)) { | ||
| if (t.getCallSignatures().some(matcher)) { | ||
| return true; | ||
| } | ||
| } | ||
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| return false; | ||
| } | ||
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| function isFunctionParam( | ||
| checker: ts.TypeChecker, | ||
| param: ts.Symbol, | ||
| node: ts.Node, | ||
| ): boolean { | ||
| const type: ts.Type | undefined = checker.getApparentType( | ||
| checker.getTypeOfSymbolAtLocation(param, node), | ||
| ); | ||
| for (const t of tsutils.unionTypeParts(type)) { | ||
| if (t.getCallSignatures().length !== 0) { | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| function isPromiseCatchCallWithHandler(expression: ts.CallExpression): boolean { | ||
| return ( | ||
| tsutils.isPropertyAccessExpression(expression.expression) && | ||
| expression.expression.name.text === 'catch' && | ||
| expression.arguments.length >= 1 | ||
| ); | ||
| } | ||
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| function isPromiseThenCallWithRejectionHandler( | ||
| expression: ts.CallExpression, | ||
| ): boolean { | ||
| return ( | ||
| tsutils.isPropertyAccessExpression(expression.expression) && | ||
| expression.expression.name.text === 'then' && | ||
| expression.arguments.length >= 2 | ||
| ); | ||
| } |
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