D Language Foundation October/November 2023 Planning Updates

[Mike Parker]

## October
We had no regular planning sessions in October. Instead, there 
were two workgroup meetings focused on DMD as a library. These 
took place after the monthly meeting and involved several people 
who were stakeholders, were interested in the project, or had 
some level of experience with it. The invitation list included 
Dennis Korpel, Jan Jurzitza (WebFreak), Prajwal S N, Razvan Nitu, 
Ali Çehreli, Luís Ferreira, Martin Kinkelin, and Walter Bright.

The main focus of these meetings was a proposal Razvan had 
regarding the possibility of overriding AST Nodes, something 
[he'd brought up in our September 
meeting](https://forum.dlang.org/thread/hetwfhikjqwzlvywmyzc@forum.dlang.org). His idea was to enable it via mixins. Walter was reluctant to take that approach and suggested AST nodes should just be simple classes with fields and helper methods. That approach would simplify how AST families are created, but wouldn't fix the underlying issue of being unable to override a node's behavior. (Also see [Razvan's DConf '23 talk on the topic](https://youtu.be/eKT3MYpRgYA).)

In the end, they agreed to refactor the AST implementation by 
pulling all semantic routines and fields out of the AST nodes so 
that `ASTBase` will only contain imports of AST nodes as opposed 
to the duplicate implementations it contains now. Once this is 
complete, they'll revisit Razvan's idea about the mixins.

Razvan has since gotten started on this project. You can [track 
its progress in our project 
tracker](https://github.com/orgs/dlang/projects/41/views/1). He 
recently [published a blog 
post](https://dlang.org/blog/2024/02/22/dmd-compiler-as-a-library-a-call-to-arms/) as a call to arms seeking assistance. A handful of people have stepped up, but there's still a lot of work. Anyone looking to make some impactful contributions should read the blog post and [the relevant section of the contributor guide](https://github.com/dlang/dmd/blob/master/CONTRIBUTING.md#refactoring-the-dmd-ast) to learn how to help out.

## November
We had one planning session in November. It was held the week 
before our monthly meeting. The main points of discussion were 
details about the Bugzilla to GitHub migration and more 
implementation details for DMD as a library.

For the former, Robert had already migrated the Visual D issues 
and wanted feedback on the order in which to migrate the 
remaining projects. Everyone agreed he should go from the project 
with the lowest issue count to the highest. We also discussed 
some details about dlang-bot, how to handle attachments, and some 
more implementation details.

The other issue was regarding `extern(C++)` classes in DMD. These 
are `extern(C++)` so that they're available to LDC, GDC, and any 
other future tools and compilers that need to integrate the D 
compiler into a C++ codebase. However, this had caused problems 
for people using DMD as a library in practice. For example, 
forgetting that the class is `extern(C++)` when subclassing it; 
this caused problems when trying to use features unavailable for 
`extern(C++)`, e.g., dynamic arrays. There was a workaround for 
that particular case, but a new one had popped up when the 
overriding class was templated and was instantiated with, e.g., a 
dynamic array type.

Razvan expected this would continue to be an annoying problem and 
was looking for ideas to solve it. We discussed the possibility 
of making the DMD as a library classes `extern(D)` instead. 
Ultimately, the consensus was that though the visitor classes 
could be made such, there was no simple way to do it for the AST 
nodes. We have more important issues than this to focus on right 
now.