xds interop: Fix buildscripts not continuing on a failed test suite

[sergiitk]

Apparently there's a difference between bash 3 and bash 4. OSX comes with bash 3 out-of-box, so for whoever wrote this logic it "worked on my machine".

[sergiitk]

Same as grpc/grpc#32093.
Proof of concept fix: https://source.cloud.google.com/results/invocations/f076d25c-105b-48ee-a722-b17126b83604

[murgatroid99]

I think I understand why the current code might not be working: the (( construct returns a 0 exit code if the value is non-zero. Since the value starts at 0 and we do a post-increment, it will always fail the first time. If that is the problem, changing it to a pre-increment should fix it.

I don't understand how adding && true could ever possibly do anything. It's like writing && true in other languages.

[sergiitk]

&& true ensures the exit code of this op is always true. It's like || true used in bash to suppress an exit of command that failed. https://stackoverflow.com/questions/11231937/bash-ignoring-error-for-a-particular-command

In this case, we're doing the same, just after the increment op.

But good idea with the pre-increment. I'll give it a try.

[sergiitk]

Yep, you're right. Pre-increment works. However, the && true change's already merged to the other repos. @murgatroid99 Would you be ok accepting this as is? Or you feel strongly about it?

[sergiitk]

Address the feedback: use pre-increment instead of && true

EDIT: this was supposed to be the commit message