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

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added inline comments.


================
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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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.


Repository:
  rC Clang

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D54903/new/

https://reviews.llvm.org/D54903