fix(tvix/eval): skip inherit with no explicit parent in let r/4528

Using `inherit` in a let-binding can not possibly have an effect, as
the given identifier is already bound exactly the same way in the
current scope.

This introduces a subtle bug that is fixed later on, as there
actually *is* a (single) condition where these inherits are
meaningful.

Change-Id: I8b24f0edcfe80db8153bb7e86cf478d36957d6f8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6192
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

1 files changed, 7 insertions, 2 deletions

diff --git a/tvix/eval/src/compiler.rs b/tvix/eval/src/compiler.rs
index ac630360d4..e2d194e8dd 100644
--- a/tvix/eval/src/compiler.rs
+++ b/tvix/eval/src/compiler.rs
@@ -676,8 +676,13 @@ impl Compiler {
             });
         }
 
-        for _ in node.inherits() {
-            todo!("inherit in let not yet implemented")
+        for inherit in node.inherits() {
+            match inherit.from() {
+                // Within a `let` binding, inheriting from the outer
+                // scope is practically a no-op.
+                None => continue,
+                Some(_) => todo!("let inherit from attrs"),
+            }
         }
 
         // Now we can compile each expression, leaving the values on