hh_client rapid restart loop when .hhconfig parsing calls failwith

[ssandler]

I was hoping to use forward_compatibility_level as a nice way of alerting people when their local hhvm installation is out of date, instead of hh_client returning a lot of errors to them because the code depends on a newer version. However this isn't practical in 3.29 or 3.28 due to this issue.

HHVM Version

$ hh_client --version
hh-d968c089ca41c9afc68c35c8fabcb4154f12d2bc-3.29.0 Mon Oct 22 09:53:31 2018

Operating System and Version

MacOS High Sierra

Standalone code, or other way to reproduce the problem

in .hhconfig with an empty repo:

forward_compatibility_level = 3.30

... or ... (edit)

enable_tc_migration_flags=foo

Then run hh_client

Actual result

hh_client rapidly loops and restarts infinitely, it's impossible to get it to stop without killing the terminal tab or restarting

Expected result

A useful error is printed stating that your hhvm version is below the required version.

Edit: failwith message is printed

[fredemmott]

I was hoping to use forward_compatibility_level as a nice way of alerting people when their local hhvm installation is out of date

The expected behavior is that there should be no error/warning for a future date - and a configuration error if configured with a release version - it's not suitable for a backwards compatibility check.

That said ,this is an issue with configuration parsing failing; you can avoid this issue by setting a date instead -

hhvm/hphp/hack/src/options/forwardCompatibilityLevel.ml

Line 51 in b946c38

| OSS_3_26 -> 2018_04_23

has the past ones, and 3.30 is 20181203

[fredemmott]

hh_client rapidly loops and restarts infinitely, it's impossible to get it to stop without killing the terminal tab or restarting

as an aside, ^Z works

[fredemmott]

Actually, I think there's 3 issues here:

• failwith shouldn't cause an infinite loop (T35898995)
• given the intended purpose of allowing things to typecheck on slightly newer versions, it should be smarter, and try to figure out if the version is newer than it understands, and ignore it if so
• feature request: add a backwards_compatibility_level= flag with your original expected behavior (Feature request: backward_compatibility_level #8377)