refactor(tvix/eval): add NixAttrs::contains function r/4597

This avoids copying around the value more than needed.

Change-Id: I35949d16dad7fb8f76e0f641eaccf48322144777
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6263
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index 4109691992..bbff79fc0d 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -66,6 +66,14 @@ impl AttrsRep {
             AttrsRep::Map(map) => map.get(&key.into()),
         }
     }
+
+    fn contains(&self, key: &str) -> bool {
+        match self {
+            AttrsRep::Empty => false,
+            AttrsRep::KV { .. } => key == "name" || key == "value",
+            AttrsRep::Map(map) => map.contains_key(&key.into()),
+        }
+    }
 }
 
 #[repr(transparent)]
@@ -202,6 +210,10 @@ impl NixAttrs {
         self.0.select(key)
     }
 
+    pub fn contains(&self, key: &str) -> bool {
+        self.0.contains(key)
+    }
+
     /// Implement construction logic of an attribute set, to encapsulate
     /// logic about attribute set optimisations inside of this module.
     pub fn construct(count: usize, mut stack_slice: Vec<Value>) -> EvalResult<Self> {