[llvm-dev] Extending the SouceMgr

[lxsameer via llvm-dev]

I think a bit of pseudo code might be good to demonstrate roughly what I had in mind:
```
template <typename ConcreteType, template <typename T> class... Traits>
class WithTrait : public Traits<ConcreteType>... {
protected:
  WithTrait(){};
  friend ConcreteType;
};

template <typename ConcreteType, template <typename> class TraitType>
class TraitBase {
protected:
  ConcreteType &Object() { return static_cast<ConcreteType &>(*this); };
};

template <typename ConcreteType>
class SourceMgr : public TraitBase<ConcreteType, SourceMgr> {
public:
  .... source mgr interface functions ....
};

class DefaultSourceMgr : public WithTrait<DefaultSourceMgr, SourceMgr> {
..... implementation ....

}
```
This way function that want to use SourceMgr would need a template but that template can be defaulted to `DefaultSourceMgr`.  I hope I could demonstrate my thoughts clear enough.

As for the functionality I need in the sourcemgr, my compiler uses namespaces as the center piece and the unit of compilation, i want my source manager to accept a namespace name and load the source code of that namespace. At the moment I had to copy paste the llvm::SourceMgr and manually tweak it.

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, September 7th, 2021 at 1:03 AM, David Blaikie <dblaikie at gmail.com> wrote:

> On Mon, Sep 6, 2021 at 4:58 PM lxsameer <lxsameer at lxsameer.com> wrote:
> 

> > Sorry about the terminology, I was thinking about CRTP style traits. I see CRTP based classes and templates quite often it the LLVM source code.
> 

> Yeah, there's a fair bit of CRTP, and traits, but they are different things - https://www.internalpointers.com/post/quick-primer-type-traits-modern-cpp discusses traits, for some details.
> 

>  
> 

> > So I think the current SourceMgr can be renamed to something like `DefaultSourceManager` that implement the `SourceMgr` CRTP trait ( sorry I don't know the exact term here).
> 

> I'm still a bit unclear on how the existing SourceMgr-using code would work - it'd have to be updated to be templated on the specific SourceMgr implementation in use, would it? Some other ideas?
> 

> Might be worth a more narrowly defined discussion about what extensibility/features you're looking for in SourceMgr, without the need to create a whole new hierarchy.
> 

>  
> 

> > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> > On Tuesday, September 7th, 2021 at 12:50 AM, David Blaikie <dblaikie at gmail.com> wrote:
> > 

> > > On Mon, Sep 6, 2021 at 3:59 PM lxsameer via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> > > 

> > > > Hey folks,
> > > > 

> > > > Hope you're doing well.
> > > > 

> > > > It seems to me that it is not possible to extend the current behavior  of `llvm::SourceMgr` (at least I couldn't think of any solution) and it is quite C/C++ish ( for lack of a better word).
> > > > 

> > > > For my use case, I need to tweak it a little bit and since there is now way to do that, I have to write my own which means I'm going to lose the ability to use any llvm api that expect a source manager and that's a big price to pay.
> > > > 

> > > > It seems that the source manger will benefits from a trait like design. This way, any front end that need a customized source manager can easily do that and the current source manager would be an implementation of that trait.
> > > 

> > > I /think/ the C++ terminology that's a closer match for what you're describing might be a "concept" rather than a "trait"?
> > > 

> > > But then, if I'm understanding correctly, all the code that currently is written in terms of the SourceMgr would have to become a template so it can be used by different implementations of the SourceMgr concept? That, at first guess, seems unlikely/infeasible?
> > > 

> > >  - Dave
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