[PATCH] D54903: [Sema] Improve static_assert diagnostics.

[Clement Courbet via Phabricator via cfe-commits]

courbet marked an inline comment as done.
courbet added inline comments.


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Comment at: test/SemaCXX/static-assert.cpp:111
+static_assert(std::is_same<ExampleTypes::T, ExampleTypes::U>::value, "message"); // expected-error{{static_assert failed due to requirement 'std::is_same<int, float>::value' "message"}}
+static_assert(std::is_const<ExampleTypes::T>::value, "message");                 // expected-error{{static_assert failed due to requirement 'std::is_const<int>::value' "message"}}
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Quuxplusone wrote:
> aaron.ballman wrote:
> > courbet wrote:
> > > Quuxplusone wrote:
> > > > I would like to see some more realistic test cases. I suggest this test case for example:
> > > > ```
> > > > struct BI_tag {};
> > > > struct RAI_tag : BI_tag {};
> > > > struct MyIterator {
> > > >     using tag = BI_tag;
> > > > };
> > > > struct MyContainer {
> > > >     using iterator = MyIterator;
> > > > };
> > > > template<class Container>
> > > > void foo() {
> > > >     static_assert(std::is_base_of_v<RAI_tag, typename Container::iterator::tag>);
> > > > }
> > > > ```
> > > > This is an example where as a programmer I would not want to see //only// `failed due to requirement std::is_base_of_v<RAI_tag, BI_tag>` — that doesn't help me solve the issue. OTOH, since every diagnostic includes a cursor to the exact text of the `static_assert` already, I think it's fair to say that the current diagnostic message is redundant, and therefore it's okay to replace it (as you propose to do) with something that is not redundant.
> > > > I think it's fair to say that the current diagnostic message is redundant, and therefore it's okay to replace it (as you propose to do) with something that is not redundant.
> > > 
> > > Yes, the proposal here might not be the *best* possible diagnostic for all cases, but it's already a huge improvement on the existing one, and solves a significant proportion of use cases.
> > > 
> > > Here, the programmer will see:
> > > ```
> > > test.cc:13:5: error: static_assert failed due to requirement 'std::is_base_of<RAI_tag, BI_tag>::value'
> > >     static_assert(std::is_base_of<RAI_tag, typename Container::iterator::tag>::value);
> > >     ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > ```
> > > which I think is a reasonable help for debugging.
> > > 
> > @Quuxplusone, do you have recommendations for what you'd prefer to see instead?
> > 
> > FWIW, I think this is a good incremental improvement. If there's more information we could display easily as part of this patch, we should consider it, but I'm also fine with saying this is progress.
> > @Quuxplusone, do you have recommendations for what you'd prefer to see instead?
> 
> On the diagnostic itself, no, this looks good and I was just thinking out loud.
> 
> On the test cases, yes, I suggest that there should be at least one test case where a `static_assert` appears inside a template and uses something template-dependent.
SG, I'll add such an example (with std::is_same if you don't mind to avoid having to duplicate the whole `<type_traits>` in the test :) )


Repository:
  rC Clang

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  https://reviews.llvm.org/D54903/new/

https://reviews.llvm.org/D54903