Hi!

I tried to hack a bit on dmd to have it generate a C++ header for a D module. I've copied the visitor in hdrgen.d and did truly terrible things to it, to the point where I don't feel confident that I want to show that code to anyone.

So now I get something almost resembling C++ code for a few really trivial definitions in the input D module. But that is for all definitions, not just the ones marked external(C++).

This is the point where I'm actually stumped now. The PrettyPrintVisitor, which I used as a template, does not really make it easy to discover the context of a visited AST node. In particular, I don't know how to determine if one of the parent nodes possess the required extern(C++) linkage specification to be considered for exporting.

If there was a way for the visitor to know when the subtree below a certain node has been visited completely, it could then trivially track linkage as a kind of a contextual information.

So to anyone who knows dmd better than me: how would you go about implementing the visitor in such a way that it only exports the correct AST subtrees?

Gregor

On Tuesday, 19 March 2019 at 20:55:34 UTC, Gregor Mückl wrote:
> If there was a way for the visitor to know when the subtree below a certain node has been visited completely, it could then trivially track linkage as a kind of a contextual information.

DFS traversal?

On 2019-03-19 21:55, Gregor Mückl wrote:
> Hi!
> 
> I tried to hack a bit on dmd to have it generate a C++ header for a D module. I've copied the visitor in hdrgen.d and did truly terrible things to it, to the point where I don't feel confident that I want to show that code to anyone.
> 
> So now I get something almost resembling C++ code for a few really trivial definitions in the input D module. But that is for all definitions, not just the ones marked external(C++).
> 
> This is the point where I'm actually stumped now. The PrettyPrintVisitor, which I used as a template, does not really make it easy to discover the context of a visited AST node. In particular, I don't know how to determine if one of the parent nodes possess the required extern(C++) linkage specification to be considered for exporting.
> 
> If there was a way for the visitor to know when the subtree below a certain node has been visited completely, it could then trivially track linkage as a kind of a contextual information.
> 
> So to anyone who knows dmd better than me: how would you go about implementing the visitor in such a way that it only exports the correct AST subtrees?

I'm not sure if you need to look at the parent. Every declaration has a "linkage" field [1] identifying if it's C++, D or something else. Classes and structs, which don't inherit from Declaration, has a "classKind" field [2].

You can also have a look at this work in progress PR [3].

[1] https://github.com/dlang/dmd/blob/3a298e504707ccd8d633c6ea5511d46c5758fa8b/src/dmd/declaration.d#L289

[2] https://github.com/dlang/dmd/blob/3a298e504707ccd8d633c6ea5511d46c5758fa8b/src/dmd/aggregate.d#L86

[3] https://github.com/dlang/dmd/pull/8591

-- 
/Jacob Carlborg

On Wednesday, 20 March 2019 at 10:27:27 UTC, Jacob Carlborg wrote:
> On 2019-03-19 21:55, Gregor Mückl wrote:
>> [snip]
> I'm not sure if you need to look at the parent. Every declaration has a "linkage" field [1] identifying if it's C++, D or something else. Classes and structs, which don't inherit from Declaration, has a "classKind" field [2].
>
> You can also have a look at this work in progress PR [3].
>
> [1] https://github.com/dlang/dmd/blob/3a298e504707ccd8d633c6ea5511d46c5758fa8b/src/dmd/declaration.d#L289
>
> [2] https://github.com/dlang/dmd/blob/3a298e504707ccd8d633c6ea5511d46c5758fa8b/src/dmd/aggregate.d#L86
>
> [3] https://github.com/dlang/dmd/pull/8591

Do these fields extend properly to children? Consider the following code:

extern(C++) class C
{
  int foo(int a, int b);
}

Will foo be marked with C++ linkage? The parameters as well? That would simplify the matter a lot.

The pull request does indeed look useful. Thanks!

On Wednesday, 20 March 2019 at 14:26:17 UTC, Gregor Mückl wrote:
> On Wednesday, 20 March 2019 at 10:27:27 UTC, Jacob Carlborg wrote:
>> [...]
>
> Do these fields extend properly to children? Consider the following code:
>
> extern(C++) class C
> {
>   int foo(int a, int b);
> }
>
> Will foo be marked with C++ linkage? The parameters as well? That would simplify the matter a lot.
>
> The pull request does indeed look useful. Thanks!

It _should_ you can test it by looking if the mangle changes from the class without extern(C++).

On 2019-03-20 15:26, Gregor Mückl wrote:

> Do these fields extend properly to children? Consider the following code:
> 
> extern(C++) class C
> {
>    int foo(int a, int b);
> }
> 
> Will foo be marked with C++ linkage? 

"foo" will definitely have C++ linkage.

The parameters as well? That would simplify the matter a lot.

Not sure. I don't think that matters in this case.

-- 
/Jacob Carlborg