[llvm-dev] RFC: A cross platform way of using shell commands in lit tests

[<Alexander G. Riccio> via llvm-dev]

> The real problem is that file deletion is racy on Windows.

That's actually not strictly accurate. I filed a bug about this a while
ago: https://llvm.org/bugs/show_bug.cgi?id=27386

The reasons are really complex/subtle, and you can see more at the bug
tracker, or: Niall Douglas "Racing The File System"
https://youtu.be/uhRWMGBjlO8 ...I haven't gotten to writing the actual
patch yet. If anybody wants to pick it up, go right ahead.

Note: sent twice because I am unreasonably bad at mailing lists, and
replied wrong on the first try.

On Aug 16, 2016 2:16 PM, "Zachary Turner via llvm-dev" <
llvm-dev at lists.llvm.org> wrote:

> That's more like a workaround though.  The real problem is that file
> deletion is racy on Windows.  I can't count the number of times I've
> encountered this error, only to find out that adding a retry fixed the
> problem.  Sure, if you can remove opened files then there's no problem to
> begin with, but even if you can't, you can still remove the file by
> retrying again 100ms later or so.  It seems silly to disable a test which
> could be testing useful functionality because of some quirk of an OS.
>
> If you had your own robust rm command, it can retry a few times, allowing
> the test to run everywhere.
>
> On Tue, Aug 16, 2016 at 11:07 AM Reid Kleckner via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> On Tue, Aug 16, 2016 at 10:09 AM, Greg Bedwell via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Anecdotally, most of the times I've seen people add "REQUIRES: shell" on
>>>> a test they really meant "disable on windows". I think/hope that's
>>>> usually temporary while they investigate problems, but it might explain
>>>> why so many tests say they require shell when they don't.
>>>>
>>>>
>>> In at least one case I can think of ("clang/test/Format/style-on-command-line.cpp")
>>> the "REQUIRES: shell" is there to work around annoying intermittent
>>> failures on Windows where 'rm' was failing with permission denied errors
>>> just occasionally enough to be a problem.  I've definitely seen this happen
>>> in a number of other places previously although I can't think whether this
>>> affects any other lit tests off-hand, but I know that personally I've had
>>> to implement 'robust rm' (basically, keep on trying until the error goes
>>> away on its own) on Windows in a number of different systems to work around
>>> this sort of problem before.  Replacing gnuwin32 with something where we
>>> could easily implement something like 'robust <cmd>' versions for Windows
>>> when we encounter these sorts of issues would be fantastic, so I'm
>>> definitely in favour of removing the dependency.
>>>
>>
>> You can use "REQUIRES: can-remove-opened-file" to express this
>> requirement more precisely.
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