The assertion-arguments rule should validate message argument type

[sindresorhus]

This currently passes t.deepEqual({}, {}, {});, which can make for some hard to debug issues. @gajus reported such issue on Gitter.

We should ensure that if message is specified, it's a string. We could implement inline literal validation first, as that's pretty easy.

We should also detect the type if it's a variable defined in the same scope:

const message = 'foo';

...

t.deepEqual({}, {}, message);

@jfmengels Many rules could use some kind of naive type inference. Maybe eslint-ast-utils could add something like that?

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• #314 Add check for the assertion message to be a string

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[gajus]

Sorry forgot to raise an issue for this. Thank you, @sindresorhus .

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[GMartigny]

Should this be under a new option or by default ?
I can imagine a case where user use an object with a toString function, but I guess this is extra rare.

[novemberborn]

Should this be under a new option or by default ?

Default, I think.

AVA already validates this, so I think it's unlikely anybody will see their linter rules fail, tests would have already been failing. I don't think we need a major release for this. @sindresorhus what do you reckon?

[sindresorhus]

Agreed

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