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Recursive types with `Debug` derive cause type check overflow
This might be an inherent limitation in the Rust compiler, but trying to make recursive types derive Debug even if generic type arguments are not Debug needs a hacky workaround:
struct Undebuggable(fn());
#[derive(derive_more::Debug)]
enum Expr<A> {
#[debug("Atom(?)")]
Atom(A),
If(Branches<A>),
}
#[derive(derive_more::Debug)]
struct Branches<A> {
// remove this attribute to cause compile error:
/*```
error[E0275]: overflow evaluating the requirement `Expr<Undebuggable>: Debug`
--> playground/derive_more_debug_test/src/main.rs:25:5
|
25 | dbg!(expr);
| ^^^^^^^^^^
|
= note: required for `Vec<Expr<Undebuggable>>` to implement `Debug`
= note: 2 redundant requirements hidden
= note: required for `&Branches<Undebuggable>` to implement `Debug`
note: required by a bound in `derive_more::core::fmt::rt::Argument::<'_>::new_debug`
--> /home/nius/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/rt.rs:120:25
|
120 | pub fn new_debug<T: Debug>(x: &T) -> Argument<'_> {
| ^^^^^ required by this bound in `Argument::<'_>::new_debug`
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `dbg` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0275`.
error: could not compile `derive_more_debug_test` (bin "derive_more_debug_test") due to 1 previous error
```*/
#[debug("[{}]", exprs.iter().map(|e| format!("{e:?}")).collect::<Vec<_>>().join(", "))]
exprs: Vec<Expr<A>>,
}
// ... code that tries to debug `Expr<Undebuggable>` ...
See here for a cloneable repro repo: https://github.com/skius/derive_more_debug_test/blob/main/src/main.rs
Is there a way to do this (derive Debug with potentially non-Debug generic arguments in recursive types) with a less hacky workaround?