refactor(tvix/eval): move `unwrap_or_clone_rc` to lib module r/5254

This is more generally useful than just inside the VM, until it is
stabilised in Rust itself.

Change-Id: Id9aa3d5b533ff38e3d2c6b85ad484394fdd05dcf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7186
Tested-by: BuildkiteCI
Autosubmit: tazjin <tazjin@tvl.su>
Reviewed-by: grfn <grfn@gws.fyi>
Reviewed-by: Adam Joseph <adam@westernsemico.com>

2 files changed, 9 insertions, 6 deletions

diff --git a/tvix/eval/src/lib.rs b/tvix/eval/src/lib.rs
index 6cf3aa212a18..00f680bc7a2e 100644
--- a/tvix/eval/src/lib.rs
+++ b/tvix/eval/src/lib.rs
@@ -22,6 +22,8 @@ mod test_utils;
 #[cfg(test)]
 mod tests;
 
+use std::rc::Rc;
+
 // Re-export the public interface used by other crates.
 pub use crate::builtins::global_builtins;
 pub use crate::compiler::{compile, prepare_globals};
@@ -31,3 +33,9 @@ pub use crate::pretty_ast::pretty_print_expr;
 pub use crate::source::SourceCode;
 pub use crate::value::Value;
 pub use crate::vm::run_lambda;
+
+// TODO: use Rc::unwrap_or_clone once it is stabilised.
+// https://doc.rust-lang.org/std/rc/struct.Rc.html#method.unwrap_or_clone
+pub fn unwrap_or_clone_rc<T: Clone>(rc: Rc<T>) -> T {
+    Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone())
+}
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index c67e9f6d8899..8c45ee7363e1 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -10,6 +10,7 @@ use crate::{
     nix_search_path::NixSearchPath,
     observer::RuntimeObserver,
     opcode::{CodeIdx, Count, JumpOffset, OpCode, StackIdx, UpvalueIdx},
+    unwrap_or_clone_rc,
     upvalues::Upvalues,
     value::{Builtin, Closure, CoercionKind, Lambda, NixAttrs, NixList, Thunk, Value},
     warnings::{EvalWarning, WarningKind},
@@ -884,12 +885,6 @@ impl<'o> VM<'o> {
     }
 }
 
-// TODO: use Rc::unwrap_or_clone once it is stabilised.
-// https://doc.rust-lang.org/std/rc/struct.Rc.html#method.unwrap_or_clone
-fn unwrap_or_clone_rc<T: Clone>(rc: Rc<T>) -> T {
-    Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone())
-}
-
 pub fn run_lambda(
     nix_search_path: NixSearchPath,
     observer: &mut dyn RuntimeObserver,