hazohelet added inline comments.
================
Comment at: clang/test/SemaCXX/vartemplate-lambda.cpp:17
+ //
expected-note{{cannot be used in a constant expression}} \
+ // expected-error 2{{a
lambda expression may not appear inside of a constant expression}}
};
----------------
cor3ntin wrote:
> hazohelet wrote:
> > cor3ntin wrote:
> > > This also looks like a regression.
> > >
> > > The current error is much clearer, can you investigate?
> > > ```
> > > <source>:3:22: error: constexpr variable 't<int>' must be initialized by
> > > a constant expression
> > > 3 | static constexpr T t = [](int f = T(7)){return f;}();
> > > | ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > <source>:6:12: note: in instantiation of static data member 'S::t<int>'
> > > requested here
> > > 6 | int a = S::t<int>;
> > > | ^
> > > <source>:3:26: note: non-literal type 'S::(lambda at <source>:3:26)'
> > > cannot be used in a constant expression
> > > 3 | static constexpr T t = [](int f = T(7)){return f;}();
> > > | ^
> > > ```
> > >
> > > Why do we emt 2 errors instead of a single note? Here the error is that
> > > the initializer is not a constant expression, everything else should be
> > > notes.
> > "lambda cannot be in constant expression" error is emitted from Sema
> > against lambda expressions in constant-evaluated contexts in C++14 mode,
> > and the note is emitted from constexpr evaluator.
> > The Sema-side error is emitted twice because it is emitted both
> > before/after instantiation.
> > We can suppress one of them by ignoring it when sema is instantiating
> > variable template initializer.
> > Or we can completely suppress this Sema error against initializers to avoid
> > duplicate errors from Sema and constexpr evaluator.
> > I think "lambda cannot be in constant expression" Sema error is more
> > understandable than the constexpr evaluator note "non-literal type cannot
> > be in constant expression", so I think it is ok to keep one Sema error here.
> So maybe the issue is that we are not making the declaration invalid in sema
> when we get this error? Can you look into it?
> any opinion @aaron.ballman
I updated the patch to keep a single sema error here and stop constant
interpreter from evaluating the initializer by marking declaration invalid. I
like having one sema error here.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D155064/new/
https://reviews.llvm.org/D155064
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