chore(tvix/eval): explicitly set #[repr(transparent)] on wrappers r/4512

For representation wrappers that are used to control the visibility of
type internals, this ensures that the wrapper does not increase the
size of the type.

In practice, the optimiser likely does this anyways but it is good to
guarantee it.

Change-Id: Ic6df7d668fe6006dfbd5b6cfcfc2088afa95b810
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6178
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

3 files changed, 3 insertions, 0 deletions

diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index 0ab4538a4d8c..2efeaad41306 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -67,6 +67,7 @@ impl AttrsRep {
     }
 }
 
+#[repr(transparent)]
 #[derive(Clone, Debug)]
 pub struct NixAttrs(AttrsRep);
 
diff --git a/tvix/eval/src/value/list.rs b/tvix/eval/src/value/list.rs
index 546d2c88a55a..fab85a73ec2f 100644
--- a/tvix/eval/src/value/list.rs
+++ b/tvix/eval/src/value/list.rs
@@ -3,6 +3,7 @@ use std::fmt::Display;
 
 use super::Value;
 
+#[repr(transparent)]
 #[derive(Clone, Debug, PartialEq)]
 pub struct NixList(Vec<Value>);
 
diff --git a/tvix/eval/src/value/string.rs b/tvix/eval/src/value/string.rs
index 626cf398f2dc..122a82e04802 100644
--- a/tvix/eval/src/value/string.rs
+++ b/tvix/eval/src/value/string.rs
@@ -11,6 +11,7 @@ enum StringRepr {
     Heap(String),
 }
 
+#[repr(transparent)]
 #[derive(Clone, Debug)]
 pub struct NixString(StringRepr);