docs(tvix/nix-compat): rename as_narinfo() to to_narinfo() r/7892

This actually does a bit of allocation. There's two Vecs, one for
references and one for signatures.

We can get rid of the Vec at nar_hash.

Change-Id: Ie025309b6678f83f5b961d49ff75dcfc7da145a1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11395
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

2 files changed, 13 insertions, 5 deletions

diff --git a/tvix/store/src/proto/mod.rs b/tvix/store/src/proto/mod.rs
index dd3c18d77107..a09839c8bdf9 100644
--- a/tvix/store/src/proto/mod.rs
+++ b/tvix/store/src/proto/mod.rs
@@ -173,12 +173,16 @@ impl PathInfo {
         Ok(root_nix_path)
     }
 
-    /// With self and a given StorePathRef, this reconstructs a
+    /// With self and its store path name, this reconstructs a
     /// [nix_compat::narinfo::NarInfo<'_>].
     /// It can be used to validate Signatures, or get back a (sparse) NarInfo
     /// struct to prepare writing it out.
     ///
-    /// This doesn't allocate any new data.
+    /// It assumes self to be validated first, and will only return None if the
+    /// `narinfo` field is unpopulated.
+    ///
+    /// It does very little allocation (a Vec each for `signatures` and
+    /// `references`), the rest points to data owned elsewhere.
     ///
     /// Keep in mind this is not able to reconstruct all data present in the
     /// NarInfo<'_>, as some of it is not stored at all:
@@ -188,7 +192,7 @@ impl PathInfo {
     ///
     /// If you want to render it out to a string and be able to parse it back
     /// in, at least URL *must* be set again.
-    pub fn as_narinfo<'a>(
+    pub fn to_narinfo<'a>(
         &'a self,
         store_path: store_path::StorePathRef<'a>,
     ) -> Option<nix_compat::narinfo::NarInfo<'_>> {
@@ -197,7 +201,11 @@ impl PathInfo {
         Some(nix_compat::narinfo::NarInfo {
             flags: Flags::empty(),
             store_path,
-            nar_hash: narinfo.nar_sha256.to_vec().try_into().unwrap(),
+            nar_hash: narinfo
+                .nar_sha256
+                .as_ref()
+                .try_into()
+                .expect("invalid narhash"),
             nar_size: narinfo.nar_size,
             references: narinfo
                 .reference_names
diff --git a/tvix/store/src/proto/tests/pathinfo.rs b/tvix/store/src/proto/tests/pathinfo.rs
index 2806a8ee1d9e..36c4f33933fb 100644
--- a/tvix/store/src/proto/tests/pathinfo.rs
+++ b/tvix/store/src/proto/tests/pathinfo.rs
@@ -424,7 +424,7 @@ CA: fixed:sha256:086vqwk2wl8zfs47sq2xpjc9k066ilmb8z6dn0q6ymwjzlm196cd"#
     let path_info: PathInfo = (&narinfo_parsed).into();
 
     let mut narinfo_returned = path_info
-        .as_narinfo(
+        .to_narinfo(
             StorePathRef::from_bytes(b"pa10z4ngm0g83kx9mssrqzz30s84vq7k-hello-2.12.1.tar.gz")
                 .expect("invalid storepath"),
         )