How do I suppress flow symbol errors?

Question

I'm trying to create type definition in Flow for one of my objects. I'm not sure whether Flow support Symbols, but in such cases how could I skip this warning?

 const version: Version = this.getVersion(12345);
 const upLink: string = version[Symbol.for('__my_amazing_symbol')];

But on validating the line above, I have the following error on run flow check.

Error: src/local.js:197
197:               const upLink: string = version[Symbol.for('__my_amazing_symbol')];
                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ access of computed property/element. Computed property cannot be accessed with
197:               const upLink: string = version[Symbol.for('__my_amazing_symbol')];
                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Symbol


Found 2 errors

This is my type of such object.

declare export type Version = {
        name: string;
        version: string;
    };

Flow config

[ignore]
.*/node_modules/.*
lib/.*

[include]

[libs]
node_modules/@mod/types/lib/

[lints]

[options]
suppress_comment= \\(.\\|\n\\)*\\$FlowFixMe
unsafe.enable_getters_and_setters=true

[version]
^0.52.0

did you try // $FlowFixMe before the line, i'm seeing it in your config — eenagy, Aug 14 '17 at 10:34
also please edit your question title, should be : how do I suppress flow symbol errors ? — eenagy, Aug 14 '17 at 10:35
The // $FlowFixMe should be the valid answer. :) It works for me. I'll update the title thanks for the suggestion. — Juan Picado, Aug 14 '17 at 18:11

score 1 · Accepted Answer · answered Aug 22 '17 at 21:55

I don't think the type error has anything to do with Symbol per-se. What Flow is telling you is that you declared the Version type with keys name and version, but now you're looking up a Symbol on that object, which isn't part of the type. You'd get a similar error if you did version["randomString"], because that property isn't declared to be part of the type of Version.

As another commented has mentioned, you can ignore the error with $FlowFixMe. But this code itself might be unsafe, since you're relying on extra symbols being defined on this object but not letting Flow prove it. You could try to model your Version type in a way that avoids having to do these dynamic lookups.

(Edit: ah, ok, looks like I spoke too soon. Flow doesn't like using computer symbol keys, even though it in theory could check them. See this issue: https://github.com/facebook/flow/issues/2928)

Yeah, I was aware of the lack of support for Symbols, in the meantime `// $FlowFixMe` solves the issue. I hope Facebook solves that soon. — Juan Picado, Aug 23 '17 at 06:05

How do I suppress flow symbol errors?

1 Answers1

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