[PATCH] D72498: [clangd] Print underlying type for decltypes in hover

[Sam McCall via Phabricator via cfe-commits]

sammccall added a comment.

In D72498#1814286 <https://reviews.llvm.org/D72498#1814286>, @lh123 wrote:

> In D72498#1814008 <https://reviews.llvm.org/D72498#1814008>, @sammccall wrote:
>
> > I think i'm also comfortable with marking the linked bug as wontfix.
>
>
> The previous example is just minimal repo.
>  I think it's worth fixing in this case.
>
>   template<typename T1, typename T2>  
>   auto sum(T1 &t1, T2 &t2) ->decltype(t1 + t2))
>   {  
>   	return t1 + t2;  
>   }
>


Thanks for the clearer example! I agree that's one where it'd be nice to show the result type and hovering over `decltype` won't give it to you.

But note that this patch doesn't handle the important use case of decltype as return type, really!
imagine `cout << sum('c', 4)`, and you want to know what type the function call has.
The natural thing is to hover over the function call, you'll see "function `sum<char, int>` -> `decltype(t1 + t2)`" which is indeed pretty useless.
But this patch doesn't fix that behaviour, it only handles types of declarations.

@ilya-biryukov @kadircet what do you think about unwrapping decltype only when it's a return value (optional: of a function whose leading return type is auto) to narrowly catch this idiom?


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