.flowconfig

[ignore]

[include]

[libs]

[lints]

[options]

[strict]
nonstrict-import
unclear-type
unsafe-getters-setters
untyped-import
untyped-type-import

error.txt

$ npx flow check --show-all-branches
Error --------------------------------------------------------------------------------------------------- index.js:11:29

Cannot call await with `fs.promises.stat(...)` bound to `p` because:
 - Either cannot assign `await fs.promises.stat(...)` to `b` because `Stats` [1] is incompatible with number [2].
 - Or cannot assign `await fs.promises.stat(...)` to `b` because `Promise` [3] is incompatible with number [2].

   index.js:11:29
     11|     const b: number = await fs.promises.stat('/')
                                     ^^^^^^^^^^^^^^^^^^^^^

References:
   /private/tmp/flow/flowlib_3a8cf718/node.js:1302:40
   1302|     stat(path: FSPromisePath): Promise<Stats>,
                                                ^^^^^ [1]
   index.js:11:14
     11|     const b: number = await fs.promises.stat('/')
                      ^^^^^^ [2]
   /private/tmp/flow/flowlib_3a8cf718/node.js:1302:32
   1302|     stat(path: FSPromisePath): Promise<Stats>,
                                        ^^^^^^^^^^^^^^ [3]


Error ---------------------------------------------------------------------------------------------------- index.js:23:5

Cannot get `b.then` because property `then` is missing in `Number` [1].

   index.js:23:5
   23|     b.then // error is here, in the correct spot
           ^^^^^^

References:
   index.js:4:13
    4| const F_OK: number = fs.F_OK
                   ^^^^^^ [1]


Error ---------------------------------------------------------------------------------------------------- index.js:27:5

Cannot get `c.then` because property `then` is missing in `Number` [1].

   index.js:27:5
    27|     c.then // error is here, in the correct spot
            ^^^^^^

References:
   /private/tmp/flow/flowlib_3a8cf718/core.js:133:13
   133|     length: number;
                    ^^^^^^ [1]


Error --------------------------------------------------------------------------------------------------- index.js:30:21

Cannot call await with `fs.F_OK` bound to `p` because:
 - Either number [1] is incompatible with `Promise` [2].
 - Or cannot get `d.then` because property `then` is missing in `Number` [1].

   index.js:30:21
     30|     const d = await fs.F_OK // error is here, the wrong spot
                             ^^^^^^^

References:
   /private/tmp/flow/flowlib_3a8cf718/node.js:1172:21
   1172|   declare var F_OK: number;
                             ^^^^^^ [1]
   /private/tmp/flow/flowlib_3a8cf718/core.js:696:31
    696| declare function $await<T>(p: Promise<T> | T): T;
                                       ^^^^^^^^^^ [2]



Found 4 errors

index.js

// @flow strict
import fs, { type Stats } from 'fs'

const F_OK: number = fs.F_OK

async function testAwaitPromise() {
    // good: flow allows specifying the correct type
    const a: Stats = await fs.promises.stat('/')

    // good: flow forbids specifying an incorrect type
    const b: number = await fs.promises.stat('/')

    // BUG: missing error here, await will not return a promise
    const c: Promise<Stats> = await fs.promises.stat('/')
}

async function testAwaitNonPromise() {
    // good: flow knows awaiting non-promises is OK.
    const a: number = await F_OK

    // good: flow knows awaiting non-promises does not make them promises
    const b = await F_OK
    b.then // error is here, in the correct spot

    // good: flow does not get confused if the awaited value is external, but not imported
    const c = await Uint8Array.length
    c.then // error is here, in the correct spot

    // BUG: flow gets confused if the awaited value is imported
    const d = await fs.F_OK // error is here, the wrong spot
    d.then
}

package.json

{
  "private": true,
  "dependencies": {
    "flow-bin": "0.120.1"
  }
}

two.js

// @flow strict
import fs from 'fs'

function assertNotNull<T>(x: T | null): T {
    if (x === null) throw new Error('Argument null')
    return x
}

function testLocalValue() {
    const a = assertNotNull(5)

    // good, flow knows number has no length
    a.length
}

function testImportedValue() {
    // BUG: flow gets confused if the provided value is imported
    const a = assertNotNull(fs.F_OK) // error is here, the wrong spot
    a.length
}