<div dir="ltr">I agree with Chandler here, I think the existing \ support is very useful and do not see a compelling argument to eliminate it.<div><br></div><div>Please also keep in mind that lit is used for a number of other test suites which are not C/C++ based, so language specific arguments don't get a lot of weight from me.</div>
<div><br></div><div>I also think you are too quick to dismiss the value of being able to split very long run lines into separate easy to read and perhaps conceptually grouped sections.</div><div><br></div><div> - Daniel</div>
<div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sun, Dec 8, 2013 at 5:12 AM, Chandler Carruth <span dir="ltr"><<a href="mailto:chandlerc@google.com" target="_blank">chandlerc@google.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div class="im">On Sun, Dec 8, 2013 at 4:24 AM, Alp Toker <span dir="ltr"><<a href="mailto:alp@nuanti.com" target="_blank">alp@nuanti.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"><div>
<br>
<div>On 08/12/2013 11:22, Chandler Carruth
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">On Sun, Dec 8, 2013 at 2:11 AM, Alp
Toker <span dir="ltr"><<a href="mailto:alp@nuanti.com" target="_blank">alp@nuanti.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> I'd like to propose
deprecating and shortly thereafter removing the lit test
runner feature that concatenates RUN lines ending in a
trailing \<br>
</div>
</blockquote>
<div><br>
</div>
<div>I'm really opposed to this. Especially for the Clang
test suite where run lines are often *very* long and hard
to organize, read, and edit without this feature.</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> <br>
<b>Rationale:</b><b><br>
</b><br>
<ul>
<li>Trailing \ has a special meaning in various
language standards that we support nowadays. In the
C preprocessor, for example, it's handled _before_
comments. Various compilers handle this differently
and it introduces needless incompatibilities.</li>
</ul>
</div>
</blockquote>
<div>What incompatibilities? I've never had this be an
issue.</div>
</div>
</div>
</div>
</blockquote>
<br></div>
It's an issue if you try to run the clang tests against other
compilers, say to check compatibility with MSVC.<br>
<br>
The problem is that "the trailing backslash on a continued line is
commonly referred to as a backslash-newline" -- ie. it's handled by
the preprocessor, so has significance rather than being part of the
comment.<br>
<br>
That causes dissonance between what the compiler sees and what
lit.py sees for no particularly good reason. One of the nice
properties of lit tests is that they're also valid compiler inputs,
so trailing slash is a bit unfortunate.<br></div></blockquote><div><br></div></div><div>AFAIK, the only interesting pattern of RUN lines remains valid compiler input:</div><div><br></div><div>// RUN: ... \</div><div>
// RUN: ...</div>
<div><br></div><div>This is fine because while the '\' may "surprisingly" make continue the prior comment line, the next line consisted entirely of a comment, so whatever. Clang's warning is even silenced here, and while MSVC and GCC may warn, they still are required to accept the code.</div>
<div><br></div><div>That said, I don't think that we should make tests harder to read or write just to work around problems in other compilers.</div><div class="im"><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<br>
It less of a problem if you're just consuming the suite with make
check-all, more of a problem for authoring.<div><br>
<br>
<br>
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<div class="gmail_extra">
<div class="gmail_quote">
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<ul>
<li>Forgetting the trailing \ between two RUN lines
causes the lines to be run individually. People have
checked in tests which they believed were getting
run whereas the features being tested were actually
silently broken. I've been committing fixes for some
of these but it's exceptionally time-consuming to
hunt them down after the fact.<br>
</li>
</ul>
</div>
</blockquote>
<div>I'd like to understand the rate at which this happens
(per RUN-line? per test-file?). It's never been a problem
for me, but that is in part because I check that my tests
fail without my change in addition to passing with my
change. <br>
</div>
</div>
</div>
</div>
</blockquote>
<br></div>
If only everyone did check their changes.<br>
<br>
See r194071 where trailing backslash caused a test to always
succeed, and r194073 for the kind of long-term a broken test has on
code quality.<br>
<br>
Looking at the SVN log for test/ in clang, and to a lesser extent
LLVM core, I've been doing nearly all the no-op test fixes in the
last few months. Not all of them are related to trailing \ but those
are the most pernicious kinds.<br>
<br>
It's a bad idea to gamble that I or someone else will always be
around taking the time to manually verify old tests to see if they
do what they're meant to do.</div></blockquote><div><br></div></div><div>This mostly seems to address the challenge of fixing existing tests, which certainly is hard, but I'm more interested in the challenge of writing a new test. That is, I'm not worried about the rate at which we clean this up, but the rate at which we mess this up. if there are only a few cases of this today after 10 years, then I actually think the problem isn't very bad. Put another way, if this only happens once or twice a year, is this really the biggest problem with our test suite?</div>
<div class="im">
<div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><div><blockquote type="cite"><div dir="ltr"><div class="gmail_extra">
<div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><ul><li>Removing trailing \ will introduce the neat
property that one RUN line corresponds precisely to
one command that's executed. This is good for humans
and will enable simplifications in the test runner.</li>
</ul>
</div>
</blockquote>
<div>FWIW, I've never really had a problem that needed this.
The RUN: forms a prefix of a shell script in my head, and
I know how to read shell scripts including multiple lines.</div>
</div>
</div>
</div>
</blockquote>
<br></div>
The transformations lit does are really too complex and there's at
least one known bug to do with closed pipes that's contributing to
no-op tests (think the discussion thread was on cfe-dev).<br>
<br>
In a nutshell, the script output lit forms right now is not likely
not the pipeline you had in your head ;-)<br></div></blockquote><div><br></div></div><div>I understand that you think this is too complex, but I'm suggesting that this particular aspect of lit does not seem too complex to at least one other developer, and thus you shouldn't assume it to be true.</div>
<div class="im">
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">
<br>
We need to simplify this stuff to fix no-op test issues, and also to
achieve improved source line information.<div><br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
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<div> <br>
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<ul>
<li>Eliminating the trailing \ syntax will unblock
work on improved failure source locations in lit.
Right now, when the builders encounter a test RUN
failure it's a matter of guesswork as to which RUN
line is failing, and the cycle of
commit-fix-and-watch-buildbots is laborious. We've
all wasted time with this at some point and can
totally do better.<br>
</li>
</ul>
</div>
</blockquote>
<div>While I would very much enjoy better failure reporting,
I don't really understand why it needs this. We have a
in-python parser for the RUN: lines which understands what
lines a "command" spans?<br>
</div>
<div><br>
</div>
<div>Anyways, even though I would *really* like better
failure reporting from lit, not at the cost of less
readable tests. That's the tail wagging the dog IMO.</div>
</div>
</div>
</div>
</blockquote>
<br></div>
So, my contention is that the \ is not making the long lines more
readable, just pasting over the complexity and hiding bugs.<br>
<br>
After all, long pipelines aren't how people use the LLVM tools in
the real world</div></blockquote><div><br></div></div><div>Zero of the long *lines* that I care about involve long *pipelines*. They all involve exactly one pipeline from Clang to FileCheck.</div><div><br></div><div>
They are absolutely how Clang is used in the real world: as a compiler accepting a huge number of flags from a build system.</div><div class="im">
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">Another option is to use a different break marker and require
RUN-NEXT: on continuation lines. But my view is that long RUN lines
could do with simplification anyway, so removing the feature is a
better way forward. </div></blockquote><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">
<br>
I'll throw the ball in your court to see if you have a better
solution going forward?</div></blockquote><div><br></div></div><div>Uh, no, the ball is in your court to demonstrate that a pervasive change to the testing infrastructure of LLVM is the right direction going forward. So far you've presented the following as I see it:</div>
<div><br></div><div>1) Supposed compatibility, but I don't see *any* compatibility issues in practice and I don't know why this is a priority.</div><div>2) Risk of programmer error resulting in false-pass tests. Legitimate concern, still looking to quantify how bad this problem is.</div>
<div>3) Simplicity of the RUN-lines themselves. I disagree with your assessment, so there at least doesn't appear to be clear agreement here.</div><div>4) Ability to provide accurate source locations. However, it doesn't seem necessary to me as lit already correctly understands the set of lines concatenated.</div>
<div><br></div><div>Of these, #2 is the one I really agree with. However, there are a *large* number of ways to mess this up. It's not clear that this is the most common and should thus be the priority.</div><div><br>
</div><div>On the other hand, I've presented a couple of reasons why the status quo seems a good thing:</div><div><br></div><div>a) We need the ability to wrap long RUN lines for readability. This is a real need in Clang's test suite, and I've seen it used well in LLVM's as well.</div>
<div>b) The '\' character is widely used in shell, and RUN lines are (for better or worse) a small subset of shell, so it seems reasonable to use them for familiarity.</div></div></div></div>
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