[llvm-dev] Swallowing of input in FileCheck

Reid Kleckner via llvm-dev llvm-dev at lists.llvm.org
Fri Jul 7 14:19:12 PDT 2017

On Fri, Jul 7, 2017 at 1:20 PM, George Karpenkov via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Thus, I propose modifying FileCheck default behavior to dump all swallowed
> output on stderr when the test has failed.
> Would there be any objections to such a change?


> I understand the concern that log files might become unnecessarily large,
> but since it would only be done for failed
> test I think the added readability would be worth it.

I disagree, it would be too much output. During development, it's pretty
common to cause tens of tests to fail. I don't really want 10 entire
assembly files dumped into my console during incremental development. Our
test output is already long, and I wish it were shorter.

I agree that this is a real problem when remote buildbots in different
configurations get involved. Locally debugging FileCheck failures is easy,
you just copy-paste the command like you said and pipe it to less. It's
only a pain when you aren't sure if a failure on a bot will reproduce
locally. So, I would be in favor of an option to lit that we enable on
buildslaves that dumps the output. We already have a '\bFileCheck\b'
substitution in lit. We'd just expand it to 'FileCheck --dump-on-failure'
or something on bots.
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