refactor(tvix/eval): Box Value::String r/7467

NixString is *quite* large - like 80 bytes - because of the extra
capacity value for BString and because of the context. We want to keep
Value small since we're passing it around a lot, so let's box the
NixString inside Value::String to save on some memory, and make cloning
ostensibly a little cheaper

Change-Id: I343c8b4e7f61dc3dcbbaba4382efb3b3e5bbabb2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10729
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index 2027653c3f..6fd43e064c 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -360,7 +360,7 @@ impl NixAttrs {
             let key = stack_slice.pop().unwrap();
 
             match key {
-                Value::String(ks) => set_attr(&mut attrs, ks, value)?,
+                Value::String(ks) => set_attr(&mut attrs, *ks, value)?,
 
                 Value::Null => {
                     // This is in fact valid, but leads to the value
@@ -414,9 +414,13 @@ impl IntoIterator for NixAttrs {
 fn attempt_optimise_kv(slice: &mut [Value]) -> Option<NixAttrs> {
     let (name_idx, value_idx) = {
         match (&slice[2], &slice[0]) {
-            (Value::String(s1), Value::String(s2)) if (*s1 == *NAME_S && *s2 == *VALUE_S) => (3, 1),
+            (Value::String(s1), Value::String(s2)) if (**s1 == *NAME_S && **s2 == *VALUE_S) => {
+                (3, 1)
+            }
 
-            (Value::String(s1), Value::String(s2)) if (*s1 == *VALUE_S && *s2 == *NAME_S) => (1, 3),
+            (Value::String(s1), Value::String(s2)) if (**s1 == *VALUE_S && **s2 == *NAME_S) => {
+                (1, 3)
+            }
 
             // Technically this branch lets type errors pass,
             // but they will be caught during normal attribute