[PATCH] D141826: [WIP][clang][TemplateBase] Add IsDefaulted bit to TemplateArgument

[David Blaikie via Phabricator via cfe-commits]

dblaikie added a comment.

In D141826#4072609 <https://reviews.llvm.org/D141826#4072609>, @Michael137 wrote:

> In D141826#4059088 <https://reviews.llvm.org/D141826#4059088>, @erichkeane wrote:
>
>> In D141826#4059073 <https://reviews.llvm.org/D141826#4059073>, @Michael137 wrote:
>>
>>> In D141826#4058866 <https://reviews.llvm.org/D141826#4058866>, @erichkeane wrote:
>>>
>>>> This seems innocuous enough/easy enough to use.  I'd like a comment on the functions at least and types in TemplateBase.h to specify that this is for printing-policy only?  Alternatively (and perhaps MUCH more appreciated) would be to make sure we mark the defaulted during AST generation as well.
>>>
>>> I'll have a look at doing that
>>>
>>> Are you suggesting we do the substitution check that the TypePrinter currently does when constructing the specialisation decls? So the TypePrinter simply needs to check the `TemplateArgument::getIsDefaulted`? I like the sound of that.
>>>
>>> Unfortunately we'd still need the `setIsDefaulted` because of the DWARF limitation in LLDB
>>
>> Yes, thats my thought.  Of course we'd still need the 'setIsDefaulted', but at least it would be something that coudl be generally useful.
>
> So I've been having a go at this. The latest diff sets the bit when creating `ClassTemplateSpecializationDecl`s. However, we end up having to copy the `ArrayRef<TemplateArgument>` twice (because of the current assumptions that a `TemplateArgumentList` is immutable, which seems like a nice property to maintain). That seems iffy.
>
> I also had to add the flag to the `TemplateArgument` tablegen description to support deserialized `ClassTemplateSpecializationDecl`.
>
> I've been playing around with setting the flag at construction of `TemplateArgument`s instead. Not sure how much cleaner that's going to be because so far I've not found a good single point of entry (been looking at CheckTemplateArgumentList <https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaTemplate.cpp#L6004-L6116> in `SemaTemplate`)

Yep, I think that'd be the idea, if there's somewhere to do it - rather than updating/copying it on every specialization.


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