Tslint: Cannot get `no-floating-promises` to work

[dscho]

Bug Report

• __TSLint version__: 5.10.0
• __TypeScript version__: Version 2.8.3
• __Running TSLint via__: CLI (node_modules\.bin\tslint --project tsconfig.json *.ts *\*.ts)

TypeScript code being linted

import * as fs from "fs";
import * as util from "util";
const stat = util.promisify(fs.stat);

export async function isDirectory(path: string): Promise<boolean> {
    try {
        if ((await stat(path)).isDirectory()) {
            return true;
        }
    } catch (reason) {
        /* it's okay */
    }
    return false;
}

(async (): Promise<void> => {
    if (isDirectory("123")) {
        console.log("well, hello 123!");
    }
})();

with tslint.json configuration:

{
    "extends": "tslint:recommended",
    "rules": {
        "max-line-length": {
            "options": [80]
        },
        "no-floating-promises": true,
        "no-unused-expression": true,
        "no-unused-variable": true
    }
}

Actual behavior

TSLint does not warn about the return value of isDirectory() (called in the 4th-last line in the code snippet) being a Promise that is never handled (missing await).

Expected behavior

I would hope that TSLint saves me from the many awaits I regularly omit by mistake.

[jkillian]

Looks like TSLint is examining expressions inside of conditionals; seems like a bug that should get fixed!

[dscho]

Status: Accepting PRs

@JKillian Okay, I'll bite.

However, I need guidance. I would appreciate pointers where to start fixing this (and where to add a regression test), but first I need to get npm run compile to run, which fails for me (both on Windows and on Linux):

$ npm run compile

> [email protected] compile /home/virtualbox/3rdparty/tslint
> npm-run-all -p compile:core compile:test -s compile:scripts


> [email protected] compile:test /home/virtualbox/3rdparty/tslint
> tsc -p test


> [email protected] compile:core /home/virtualbox/3rdparty/tslint
> tsc -p src


> [email protected] compile:scripts /home/virtualbox/3rdparty/tslint
> tsc -p scripts

node_modules/json-stringify-pretty-compact/index.d.ts(7,12): error TS2300: Duplicate identifier 'stringify'.
scripts/custom-typings.d.ts(3,14): error TS2300: Duplicate identifier 'stringify'.
npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! [email protected] compile:scripts: `tsc -p scripts`
npm ERR! Exit status 2
npm ERR!
npm ERR! Failed at the [email protected] compile:scripts script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/virtualbox/.npm/_logs/2018-06-28T10_22_50_693Z-debug.log
ERROR: "compile:scripts" exited with 2.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! [email protected] compile: `npm-run-all -p compile:core compile:test -s compile:scripts`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the [email protected] compile script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/virtualbox/.npm/_logs/2018-06-28T10_22_50_812Z-debug.log

What gives?

[dscho]

What gives?

I worked around, of course, by commenting out the custom typings, but it would still be good to know whether TSLint's source code is considered to be in a healthy state ;-)

Also, could you clarify what you mean by

Looks like TSLint is examining expressions inside of conditionals

Where in the code did you see that?

[dscho]

Oh, and it would appear that my understanding of what no-floating-promises is incorrect :-( There is an explicit test in test/rules/no-floating-promises/promises/test.ts.lint to verify that it does not report an unawaited Promise in a conditional:

while (returnsPromiseFunction());

So now I need even more guidance. Is this a bug in no-floating-promises' design? What is the sense of letting while (returnsPromiseFunction()); go unreported?

[jpike88]

I have the same problem. It just doesn't work.

[Christilut]

Same problem here, bit me multiple times already...

I have a simple async function that executes 1 function. That function returns a Promise<void> and omitting the await shows no tslint error.

[JoshuaKGoldberg]

while (returnsPromiseFunction());

@dscho yes, this is intentional. That is technically not a "floating" promise, as the promise is being used (as silly as that sounds).

This issue is a duplicate of #3983 and this should be better documented per #4117.