我实现了非 tracked structs 结构的, 或者说是递归型式的例子. 但不知道怎么来实现tracked的例子.

也许可能是手动展开如下代码? 另外,如果可行,那如何derive两次呢?

#[tracked]
fn data(&self, db: &DbType<'_>) -> SourceProgramData {
        SourceProgramData {
            // text: self.text(db).clone(),
            text: Test::<String, DbType<'_>, String>::match_data_type(self.text(db), db),
        }
    }

递归型式的例子:

use derive_new::new;
use ordered_float::OrderedFloat;

use crate::db::{self, Database};

// ANCHOR: input
#[salsa::input]
pub struct SourceProgram {
    #[return_ref]
    text: String,
}

pub struct SourceProgramData {
    text: String,
}
/// impl DataWithDb for T, for get TData
trait DataWithDb<Db: ?Sized, TData> {
    fn data(&self, db: &Db) -> TData;
}
type DbType<'a> = <crate::Jar as salsa::jar::Jar<'a>>::DynDb;
impl DataWithDb<DbType<'_>, SourceProgramData> for SourceProgram {
    fn data(&self, db: &DbType<'_>) -> SourceProgramData {
        SourceProgramData {
            // text: self.text(db).clone(),
            text: Test::<String, DbType<'_>, String>::match_data_type(self.text(db), db),
        }
    }
}
trait Fallback<Db>
where
    Db: ?Sized,
{
    fn match_data_type<'a, 'b: 'a, T: Clone>(a: &T, db: &'b Db) -> T {
        a.clone()
    }
}

impl<T, Db> Fallback<Db> for T
where
    T: ?Sized,
    Db: ?Sized,
{
}

#[allow(dead_code)]
impl<T, Db, TData> Test<T, Db, TData>
where
    T: DataWithDb<Db, TData>,
    Db: ?Sized,
    TData: Sized,
{
    fn match_data_type<'a, 'b: 'a>(a: &'a T, db: &'b Db) -> TData {
        a.data(db)
    }
}

struct Test<T: ?Sized, Db: ?Sized, TData: Sized>(
    core::marker::PhantomData<T>,
    core::marker::PhantomData<Db>,
    core::marker::PhantomData<TData>,
);

#[test]
fn getData() {
    let mut db = db::Database::default();
    let source_program = SourceProgram::new(&mut db, "aaa".into());
    println!("{:#?}", source_program.data(&db).text);
}