Prost broken afer nightly-2017-12-31 (due to memchr change?)

[jedisct1]

Prost code generation fails after (but not including) nightly-2017-12-31: https://github.com/danburkert/prost/issues/66

panicked at 'byte index 1 is not a char boundary; it is inside '\u{1}' (bytes 0..1)

Repository with a minimal test case for that issue: https://github.com/jedisct1/prostate

Maybe due to b65f0be ?

[danburkert]

Likely a dupe of #47175.

[kennytm]

Closing as duplicate for #47175.