t.throw flow type check is giving a false-positive (Callable signature not found in)

[gajus]

Description

I am getting an "Callable signature not found in" when using t.throws.

The type error originates in the node_modules/ava/index.js.flow definition.

This could be simply me misunderstanding what the error is saying.

I'd expect Flow to pickup:

throws(value: Promise<mixed>, error?: ErrorValidator, message?: string): Promise<mixed>;

annotation and ignore:

throws(value: () => void, error?: ErrorValidator, message?: string): mixed;

I even explicitly cast the result to Promise<void>.

If I remove the Promise<void> cast, I am getting a different error, https://gist.github.com/gajus/5c42f0262874a2bae7842691eea28a60#file-ava-flow-sh-L2.

Test Source

test('timesout after 60 seconds', async (t): Promise<void> => {
  const {
    document
  } = createDocument();

  global.document = document;

  const result: Promise<void> = loadScript('http://dailymail.co.uk/');

  clock.tick(6e4 + 1);

  t.throws(result, 'Script loading time has exceeded the maximum configured time limit.');
});

Error Message & Stack Trace

$ flow
node_modules/ava/index.js.flow:71
 71: 	throws(value: () => void, error?: ErrorValidator, message?: string): mixed;
     	              ^^^^^^^^^^ function type. Callable signature not found in
 94:   t.throws(result, 'Script loading time has exceeded the maximum configured time limit.');
                ^^^^^^ Promise. See: test/utilities/loadScript.js:94


Found 1 error

Config

Copy the relevant section from package.json:

{
  "ava": {
    "babel": {
      "plugins": [
        "transform-flow-strip-types",
        "transform-async-to-generator",
        "transform-es2015-modules-commonjs"
      ]
    },
    "require": [
      "babel-register"
    ]
  }
}

Command-Line Arguments

ava

Environment

Tell us which operating system you are using, as well as which versions of Node.js, npm, and AVA. Run the following to get it quickly:

Node.js v7.2.1
darwin 16.1.0
0.17.0
3.10.10

[jamestalmage]

pinging @thejameskyle

[gajus]

Can this be marked as a bug?

I am not sure how to fix it... I would raise a PR otherwise.

It is breaking our integration tests. Annoyingly, I cannot even use FlowFixMe comment because it then throws error in ava definition. Therefore, we had to comment out async tests just to make Flow stop complaining about these assertions.

[gajus]

@leebyron Could you have a look at this issue please?

(Since you have tackled a similar issue here #1164.)

[leebyron]

Taking a look - I'm not 100% sure what's wrong, but the js.flow file seems like it might be double-defining the throws type.

[leebyron]

A simpler repro case is simply:

t.throws(Promise.reject(new Error()))

Which yields:

index.js.flow:61
 61: 	throws(value: () => void, error?: ErrorValidator, message?: string): mixed;
     	              ^^^^^^^^^^ function type. Callable signature not found in
 13:   t.throws(Promise.reject(new Error()))
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Promise. See: test.js.flow:13