[cfe-dev] TypeLoc of a template class type in an uninstantiated template has incomplete type?

[Eric Liu via cfe-dev]

Thank you for the explanation, Jusufadis! I am just trying to see if I can
match a class template reference in a template declaration without going
into `ClassTemplateSpecializationDecl` so that I don't need to worry about
parameter substitution. But looks like I have to deal with the
substitutions.

On Wed, Feb 8, 2017 at 9:31 PM Jusufadis Bakamovic <jbakam at gmail.com> wrote:

> Hi Eric,
>
> `A<T>` in `class Temp` definition is a dependent name (see
> http://eel.is/c++draft/temp.dep) whereas in `class Temp` specialization
> it is not (it is instantiated as `A<int>`). In case of dependent names,
> clang will not offer you any additional details about the construct because
> semantics of such a construct may differ from one instantiation to another.
>
> I had a very similar question few days ago (
> http://lists.llvm.org/pipermail/cfe-dev/2017-January/052376.html).
> Although I am not using AST matcher, but rather libclang directly, I did
> end up implementing heuristic method for extracting the details that I
> needed and which seems to be quite applicable in my target use-case. I am
> not sure about your use-case and how flexible AST matcher is but you might
> want to try to jump to the declaration of dependent-name node and then walk
> through it to get more details which you need.
>
> Cheers,
> Adi
>
> On 8 February 2017 at 18:55, Eric Liu via cfe-dev <cfe-dev at lists.llvm.org>
> wrote:
>
> Hi all,
>
> I am trying to match type references of `class A` in the following code:
>
>  template <typename T>
>  class A {};
>
>  template <typename T>
>  class Temp {
>    A<int> a;
>    A<T> at;
>  };
>
> with matcher:
>     typeLoc(loc(qualType(hasDeclaration(cxxRecordDecl(hasName("A"))))))
>
> However, only `A<int>` matches, and `A<T>` only matches after I added an instantiation of the template (e.g. `Temp<int> t;`).
>
> I also dumped the AST, and it seems that `A<T>` is only associated with the `class A` in `ClassTemplateSpecializationDecl` of `Temp` but not `ClassTemplateDecl` (highlighted below).
>
> Is this expected? If so, could someone explain why TypeLoc `A<T>` in `ClassTemplateDecl` should not be associated with the actual class A? Thanks a lot!
>
>
> |-ClassTemplateDecl 0x7f991815b5d8 <line:4:1, line:8:1> line:5:7 Temp
> | |-TemplateTypeParmDecl 0x7f991815b4c0 <line:4:11, col:20> col:20 referenced typename T
> | |-CXXRecordDecl 0x7f991815b540 <line:5:1, line:8:1> line:5:7 class Temp definition
> | | |-CXXRecordDecl 0x7f991815b848 <col:1, col:7> col:7 implicit class Temp
> | | |-FieldDecl 0x7f991815bbc0 <line:6:3, col:10> col:10 a 'A<int>':'class A<int>'
> | | `-FieldDecl 0x7f991815bcc8 <line:7:3, col:8> col:8 at *'A<T>'*
> | `-ClassTemplateSpecializationDecl 0x7f991815bd48 <line:4:1, line:8:1> line:5:7 class Temp definition
> |   |-TemplateArgument type 'int'
> |   |-CXXRecordDecl 0x7f991818c000 prev 0x7f991815bd48 <col:1, col:7> col:7 implicit class Temp
> |   |-FieldDecl 0x7f991818c098 <line:6:3, col:10> col:10 a 'A<int>':'class A<int>'
> |   |-FieldDecl 0x7f991818c198 <line:7:3, col:8> col:8 at *'A<int>':'class A<int>'*
> |   |-CXXConstructorDecl 0x7f991818c220 <line:5:7> col:7 implicit used constexpr Temp 'void (void) noexcept' inline default trivial
> |   | |-CXXCtorInitializer Field 0x7f991818c098 'a' 'A<int>':'class A<int>'
> |   | | `-CXXConstructExpr 0x7f991818cc68 <col:7> 'A<int>':'class A<int>' 'void (void) noexcept'
> |   | |-CXXCtorInitializer Field 0x7f991818c198 'at' 'A<int>':'class A<int>'
> |   | | `-CXXConstructExpr 0x7f991818ccc0 <col:7> 'A<int>':'class A<int>' 'void (void) noexcept'
> |   | `-CompoundStmt 0x7f991818cd28 <col:7>
> |   |-CXXConstructorDecl 0x7f991818c8c8 <col:7> col:7 implicit constexpr Temp 'void (const class Temp<int> &)' inline default trivial noexcept-unevaluated 0x7f991818c8c8
> |   | `-ParmVarDecl 0x7f991818c9f0 <col:7> col:7 'const class Temp<int> &'
> |   `-CXXConstructorDecl 0x7f991818ca88 <col:7> col:7 implicit constexpr Temp 'void (class Temp<int> &&)' inline default trivial noexcept-unevaluated 0x7f991818ca88
> |     `-ParmVarDecl 0x7f991818cbb0 <col:7> col:7 'class Temp<int> &&'
>
>
> Regards,
> Eric
>
>
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