feat: initial commit

.gitignore

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+/target
+/Cargo.lock

Cargo.toml

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+[package]
+name = "rkyv_test"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rkyv = "*"
+tracing = "*"

src/foo_imaginary.rs

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+// note: does not compile
+
+#[derive(rkyv::Serialize, rkyv::Deserialize, rkyv::Archive)]
+pub struct Foo {
+    /// hypothetical attribute allowing a free function of signature
+    /// `Fn(<field_type>) -> <dest_type>` where `<dest_type>` implements `Archive`
+    #[archive_using(crate::tracing_level::to_u8)]
+    level: tracing::Level,
+}

src/foo_ir.rs

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+pub struct Foo {
+    level: tracing::Level,
+}
+
+#[derive(rkyv::Deserialize, rkyv::Serialize, rkyv::Archive)]
+pub struct FooIR {
+    level: u8,
+}
+
+impl From<Foo> for FooIR {
+    fn from(value: Foo) -> Self {
+        FooIR {
+            level: crate::tracing_level::to_u8(value.level),
+        }
+    }
+}
+
+impl From<FooIR> for Foo {
+    fn from(value: FooIR) -> Self {
+        Foo {
+            level: crate::tracing_level::try_from_u8(value.level).unwrap(),
+        }
+    }
+}

src/foo_with.rs

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+use rkyv::with::ArchiveWith;
+
+#[derive(rkyv::Serialize, rkyv::Deserialize, rkyv::Archive)]
+pub struct Foo {
+    #[with(TracingLevel)]
+    level: tracing::Level,
+}
+
+pub struct TracingLevel;
+impl ArchiveWith<tracing::Level> for TracingLevel {
+    type Archived = u8;
+    type Resolver = ();
+
+    unsafe fn resolve_with(
+        field: &tracing::Level,
+        _: usize,
+        _: Self::Resolver,
+        out: *mut Self::Archived,
+    ) {
+        out.write(crate::tracing_level::to_u8(*field))
+    }
+}

src/lib.rs

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+mod foo_ir;
+mod foo_with;
+mod tracing_level;

src/tracing_level.rs

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+
+pub fn to_u8(lvl: tracing::Level) -> u8 {
+    use tracing::Level;
+    match lvl {
+        Level::TRACE => 0,
+        Level::DEBUG => 1,
+        Level::INFO => 2,
+        Level::WARN => 3,
+        Level::ERROR => 4,
+    }
+}
+
+pub fn try_from_u8(lvl: u8) -> Result<tracing::Level, ()> {
+    use tracing::Level;
+    match lvl {
+        0 => Ok(Level::TRACE),
+        1 => Ok(Level::DEBUG),
+        2 => Ok(Level::INFO),
+        3 => Ok(Level::WARN),
+        4 => Ok(Level::ERROR),
+        _ => Err(()),
+    }
+}