ImportC shows the way to D3?

[Ola Fosheim Grøstad]

On Monday, 20 June 2022 at 08:05:38 UTC, claptrap wrote:
> So if D can "import" C code then could the same mechanism be 
> used to move to D3? Have the compiler compile D2 and D3 code to 
> the same AST?
>
> Disclaimer : I dont know exactly how ImportC works but it 
> sounds like it compiles C code into the same AST that D code 
> uses. Then its all compiled the same.
>
> yeah I know D3... but it could be a way to introduce breaking 
> changes without too much pain?
>
> Surely i cant be the only person who's thought of this?

Compiling to the same AST does not allow you to change semantics 
without ending up with more complex compiler internals. So you 
are limited to smaller semantic adjustments and syntax.

I've suggested somewhere else that if DMD implemented a high 
level IR between frontend and backend then you could compile D2 
and D3 to the same high level IR.

But you still have to replicate templates in both your D2 and D3 
code bases as you don't want to do D-style meta programming in 
the high level IR that sits before the backend. You also cannot 
just combine D3 with D2 templates when D2 is capable of 
introspection.

If fixing bugs and completing the semantics of D2 is time 
consuming, why would you make it even more difficult to achieve 
by merging D3 into the D2 frontend? Yes, this also applies to 
"import C". It was done at the wrong time. The internals should 
have been redesigned first to handle it gracefully.