Recursive generics
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- Rust
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Description
I tried this code alone:
trait HasParent {
type Parent: HasParent;
}
struct Visitor<'a, Type>
where Type: HasParent
{
parent: &'a Visitor<'a, Type::Parent>,
current: &'a Type
}
I expected to see this happen: Being able to compile OR error message.
I also expect the following evaluation to be possible, breaking the recursion, because no further monomorphization is necessary:
struct Library;
struct Module;
impl HasParent for Module {
type Parent = Library;
}
impl HasParent for Library {
type Parent = ();
}
impl HasParent for () {
type Parent = ();
}
which would produce
struct Visitor<'a, ()> {
parent: &'a Visitor<'a, ()>,
current: &'a ()
}
struct Visitor<'a, Library> {
parent: &'a Visitor<'a, ()>,
current: &'a Library
}
struct Visitor<'a, Module> {
parent: &'a Visitor<'a, Library>,
current: &'a Module
}
Instead, this happened: The compiler freezes.
Meta
rustc --version --verbose:
rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: x86_64-pc-windows-msvc
release: 1.74.0
LLVM version: 17.0.4
Backtrace
No backtrace available
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by compiling the standalone recursive-generics reproducer with the reported rustc 1.74.0 version and compare whether current versions still freeze. Investigate how the compiler handles the recursive associated-type instantiations in the example. Done means the compiler terminates with a diagnostic or successfully compiles the finite Module, Library, and unit chain.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 30/100