[cfe-dev] Getting template arguments from a clang::Type object

[Yitzhak Mandelbaum via cfe-dev]

You probably want to look at `ClassTemplatesSpecializationDecl`.  If you're
doing this in the context of AST matchers, then something like the
following is probably what you want:

```
AST_MATCHER_P(clang::TypeLoc, templateSpecializationTypeLoc,
              clang::ast_matchers::TypeLocMatcher, InnerMatcher) {
  auto L = Node.getAs<clang::TemplateSpecializationTypeLoc>();
  if (L.isNull()) return false;
  return InnerMatcher.matches(L, Finder, Builder);
}

AST_MATCHER_P(
    clang::TypeLoc, hasAnyTemplateArgumentLoc,
    clang::ast_matchers::internal::Matcher<clang::TemplateArgumentLoc>,
    InnerMatcher) {
  auto L = Node.getAs<clang::TemplateSpecializationTypeLoc>();
  if (L.isNull()) return false;
  for (unsigned Index = 0, N = L.getNumArgs(); Index < N; ++Index) {
    clang::ast_matchers::internal::BoundNodesTreeBuilder Result(*Builder);
    if (InnerMatcher.matches(L.getArgLoc(Index), Finder, &Result)) {
      *Builder = std::move(Result);
      return true;
    }
  }
  return false;
}

AST_MATCHER_P(clang::TemplateArgumentLoc, refersToTypeLoc,
              clang::ast_matchers::internal::Matcher<clang::TypeLoc>,
              InnerMatcher) {
  return Node.getArgument().getKind() == clang::TemplateArgument::Type &&
         InnerMatcher.matches(Node.getTypeSourceInfo()->getTypeLoc(),
Finder,
                              Builder);
}
```

These could be used in a matcher, for example, to identify a type which is
a template instantiation with any argument that refers to some type of
interest (here, identified by `inner_matcher`).
```
auto template_instantiation =
            templateSpecializationTypeLoc(hasAnyTemplateArgumentLoc(
                templateArgumentLoc(refersToTypeLoc(inner_matcher))));
```

As for AST guides, I don't know of any good ones, unfortunately. My first
place to look is clang-query (especially in godbolt.org) -- I enter a code
snippet and see what the resulting AST looks like.  To see the AST for
types, try using something like this in godbolt.org:
https://godbolt.org/z/bTaoTE. (Kudos to Richard Smith for this one...).

On Mon, Dec 21, 2020 at 9:04 AM Massa, Gert via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi All,
>
>
>
> Can anyone tell me how to get the template arguments from a clang::Type
> object? For example, if I have clang::Type for “std::vector<int>”, how do I
> get to this “int” type?
>
>
>
> When looking at the API reference I’m getting a bit lost with all the
> terminology I’m not yet familiar with, any good resources to that explains
> the terminology? Especially how templates are represented is still unclear
> to me.
>
>
>
> Thanks in advanced for your help and a huge thanks to all the LLVM and
> clang contributes!
>
>
>
> With Kind Regards,
>
> Gert Massa
>
>
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>
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