Instead of having a heap-allocated RefCountedBox to store a SyntaxData's
parent, reference-count SyntaxData itself. This has a couple of
advantages:
- When passing SyntaxData around, only a pointer needs to be passed
instead of the entire struct contents. This is faster.
- We can later introduce a SyntaxDataRef, which behaves similar to
SyntaxData, but delegates the responsibility that the parent stays
alive to the user. While sacrificing guaranteed memory safety, this
means that SyntaxData can then be stack-allocated without any
ref-counting overhead.
Instead, only reference count the SyntaxArena that the RawSyntax nodes
live in. The user of RawSyntax nodes must guarantee that the SyntaxArena
stays alive as long as the RawSyntax nodes are being accessed.
During parse time, the SyntaxTreeCreator holds on to the SyntaxArena
in which it creates RawSyntax nodes. When inspecting a syntax tree,
the root SyntaxData node keeps the SyntaxArena alive. The change should
be mostly invisible to the users of the public libSyntax API.
This change significantly decreases the overall reference-counting
overhead. Since we were not able to free individual RawSyntax nodes
anyway, performing the reference-counting on the level of the
SyntaxArena feels natural.
Instead, reference count the SyntaxData's parent. This has a couple of
advantages:
1. We eliminate a const_cast that was potentially unsafe
2. It more closely resembles the architecture on the Swift side
3. It has the potential to be optimised further if the parent can be
accessed in an unsafe, non-reference-counted way
`llvm::ArrayRef<T>` does not define `erase`. However, since the intent
here is to remove the last n elements, we can use `drop_back` instead.
Furthermore, replace the direct use of `Layout` with `getLayout()`.
This was identified by gcc 8.2.
* Generate libSyntax API
This patch removes the hand-rolled libSyntax API and replaces it with an
API that's entirely automatically generated. This means the API is
guaranteed to be internally stylistically and functionally consistent.
* Refactor Tuple Type Syntax
This patch:
- Refactors TypeArgumentListSyntax and
TypeArgumentListSyntaxData to use the SyntaxCollection and
SyntaxCollectionData APIs.
- Refactors TupleTypeElementSyntax to own its trailing comma, and
updates the tests accordingly.
- Provides an infrastructure for promoting types to use
the SyntaxCollection APIs
* Addressed comments.
* Renamed makeBlankTypeArgumentList()
* Update makeTupleType
* Changed makeTupleType to take an element list.
* Updated comment.
* Improved API for creating TupleTypeElementListSyntax'es
* Added round-trip test
* Removed last TypeArgumentList holdovers.
* Fixed round-trip test invocation
