[cfe-dev] Printing "readably"

[Manuel Klimek]

On Tue Sep 02 2014 at 5:25:32 AM Peter Stirling <peter at pjstirling.plus.com>
wrote:

> Hi,
>
> At the risk of over-promising, I'm working on a replacement for SWIG
> using clang.


Generally, a lot of people wanted to see this done, so I'd guess there'll
be some willingness to provide the functionality you need, as long as it
fits within clang's overall design choices.
It's also possible to put some of the functionality into LibTooling (don't
know whether you've considered using it for your use case).


> The basic idea is very simple: create a wrapper for each
> public function and method that is reachable from the source spec
> (ideally a system header to make it as friction free as possible). These
> wrappers will substitute pointers instead of references, objects with
> constructors, etc.
>
> Obviously, clang makes it easy to get the list of functions and methods,
> and massaging "dangerous" types to pointers isn't that hard (as an
> aside, the documentation for PointerType would benefit from a sentence
> directing you to ASTContext for getting your hands on instances
> programmatically).
>

Patches welcome :D Especially when they enhance documentation!


> I have been using QualType.print(), but it has a couple of problems:
>

Generally, the print functions are more for debugging than anything else;
my first intuitive response would be to implement some visitor for your
types that puts together the correct source code output you need...


> a) TypedefTypes aren't printed with their appropriate scope, and when I
> started using QualType.getCanonicalType() before printing (to eliminate
> typedefs),
> b) NullPtrType is printed as "nullptr_t" rather than "std::nullptr_t"
> (or even "decltype(nullptr)")
>
> Upon deciding to get my hands dirty, I investigated TypePrinter.cpp, and
> indeed printTypedefBefore() made no attempt to provide the scope of a
> typedef (even when PrintingPolicy.SuppressScope is false). I tried
> copying the relevant part of printTag(), which works for most cases, but
> now I get more subtle errors:
>
> dummy.cc.cc:12176:102: error: 'new_allocator' is not a class, namespace,
> or scoped enumeration
> __gnu_cxx::new_allocator::size_type
>
> __gnu_cxx::new_allocator is a template, but in this case size_type
> doesn't depend on a template parameter (the source uses std::size_t
> unconditionally), from what I can gather from the source, the
> TypedefDecl is given the context of the CXXRecord, (and not the
> ClassTemplateSpecializationDecl) so it doesn't know that it should be
> giving template arguments.
>
> If that is correct (is it correct?) then I don't know how I can safely
> output TypedefTypes without convincing the compiler to parse it
> differently, which puts me back to using getCanonicalType().
>
> For ElaboratedTypes I need to ignore printing the NestedNameSpecifier,
> and then NOT enable PrintingPolicy::SuppressScope (which is done by the
> ElaboratedTypePolicyRAII). My current diff for the method uses
> SuppressScope to decide whether to print the full scope, which is
> (obviously) a potentially breaking change. Arguably instead of
> SuppressScope there should be a tri-state enum AsSource/Suppress/Force
> but I don't know whether you would be interested in making such a change.
>

That is a question for Richard...

cheers,
/Manuel


>
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