flx added a comment.

In https://reviews.llvm.org/D26195#585091, @aaron.ballman wrote:

> In https://reviews.llvm.org/D26195#584958, @flx wrote:
>
> > In https://reviews.llvm.org/D26195#584730, @aaron.ballman wrote:
> >
> > > In https://reviews.llvm.org/D26195#584724, @flx wrote:
> > >
> > > > In https://reviews.llvm.org/D26195#584712, @aaron.ballman wrote:
> > > >
> > > > > Please add a test case with an incomplete type that would exercise 
> > > > > this code path, otherwise, LGTM.
> > > >
> > > >
> > > > Hi Aaron,
> > > >
> > > > do you have any advise on how to add an incomplete type? When debugging 
> > > > this I had a compilation unit that failed to compile causing it, but 
> > > > I'm not sure this is a good way to add a test case.
> > >
> > >
> > > A type like `class C;` is an incomplete type, as is `void`, so perhaps 
> > > you can find a check that would let such a construct call through to 
> > > `isExpensiveToCopy()`.
> >
> >
> > Great, this works and I was able to see the check produce a false positive 
> > without the proposed change here, but the test code introduces a compile 
> > error now due to the incomplete type used in the function definition. Is 
> > there a way to suppress that?
>
>
> Unlikely -- fixing the compile error likely makes the type not expensive to 
> copy by using a pointer (or reference). This may be tricky to test because 
> the times when you would call `isExpensiveToCopy()` is with types that are 
> going to be logically required to be complete. I am not certain the compile 
> error is actually a problem though -- I would imagine your existing 
> false-positives (that you mentioned in the patch summary) are cases where 
> there is a compile error *and* a clang-tidy diagnostic, so the test may 
> simply be "check that there's only a compile error and no clang-tidy 
> diagnostic where there used to be a false-positive one."


That's exactly the case, my question here is how can I make the test succeed in 
the face of a compile error, i.e. by expecting the error as well?


Repository:
  rL LLVM

https://reviews.llvm.org/D26195



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