feat(tvix/tools/weave): init

Scalable tracing GC for the cache.nixos.org dataset.

Change-Id: I6c7852796f28e1a1c7607384ffb55f44407e1185
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10765
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/tools/weave/src/bytes.rs

@@ -0,0 +1,27 @@
+use owning_ref::{OwningRef, StableAddress};
+use polars::export::arrow::buffer::Buffer;
+use std::ops::Deref;
+
+/// An shared `[[u8; N]]` backed by a Polars [Buffer].
+pub type FixedBytes<const N: usize> = OwningRef<Bytes, [[u8; N]]>;
+
+/// Wrapper struct to make [Buffer] implement [StableAddress].
+/// TODO(edef): upstream the `impl`
+pub struct Bytes(pub Buffer<u8>);
+
+/// SAFETY: [Buffer] is always an Arc+Vec indirection.
+unsafe impl StableAddress for Bytes {}
+
+impl Bytes {
+    pub fn map<U: ?Sized>(self, f: impl FnOnce(&[u8]) -> &U) -> OwningRef<Self, U> {
+        OwningRef::new(self).map(f)
+    }
+}
+
+impl Deref for Bytes {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}