typeof s === "symbol" yields error 'unexpected predicate "symbol"'

[jaredly]

And it can't be suppressed either.

It totally breaks things, not just a normal error.

[samwgoldman]

Issue is here. This code isn't actually unreachable, because the string inside the IsP/NotP can be provided by the user in a typeof check. We should output a normal flow error instead of asserting.

[jaredly]

But it shouldn't error. An es6 symbol has typeof "symbol"
On Mon, Aug 10, 2015 at 4:55 PM Sam Goldman [email protected]
wrote:

Issue is here

flow/src/typing/flow_js.ml

Line 4209 in 790d186

assert_false (spf "Unexpected predicate %s" (string_of_predicate p))

.
This code isn't actually unreachable, because the string inside the IsP/
NotP can be provided by the user in a typeof check. We should output a
normal flow error instead of asserting.

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#712 (comment).

[samwgoldman]

You're right. There are two issues here: 1) we assume code is unreachable when it isn't and 2) we should properly refine symbols.

[mroch]

I fixed the exception in d45c099 and filed #1015 to make typeof x === "symbol" actually work. until then, you should be able to suppress the error now.

thanks, this was a bad one.