Don't throw a TypeError when trying to decode a sum value that contains a dangerous string

[thewilkybarkid]

I've recently started to see sporadic test failures for https://github.com/PREreview/prereview.org/blob/f1909e23b7d8a27d1d97e922dbdffa42a5b84570/test/write-review.test.ts#L1560-L1617. The test is probably hard to follow, but it's failing when using https://github.com/PREreview/prereview.org/blob/f1909e23b7d8a27d1d97e922dbdffa42a5b84570/src/write-review.ts#L59-L67 to decode a value generated by fc.record({ competingInterests: fc.string() }, { withDeletedKeys: true })

The error is:

Stack trace: TypeError: members[v].decode is not a function

  at decode (node_modules/io-ts/lib/Kleisli.js:237:39)

A failing value looks like this:

{ competingInterests: 'toString' }

Fast-Check recently added a failure to generate strings containing JavaScript keywords and the like (dubzzz/fast-check#3043), revealing that io-ts crashes when trying to decode a sum type as the 'in' operator finds inherited properties such as 'toString'.

I looked at using Fast-Check in the test, but it needs to be upgraded and causes its other usages to fail, so I've just used a built-in property name instead.

[gcanti]

Thanks @thewilkybarkid, patch released