refactor(tvix/value): replace static representation with SmolStr r/4498

The only uses of the static variant were for `"name"` and `"value"`,
which are both small enough to fit into a SmolStr. The size of
NixString accomodates `String` anyways, so we may as well inline them.

Additionally smol_str is already in the dependency graph because rnix
uses it, and using it for representations of identifiers is sensible.

Change-Id: I9969312256d1657d69128e54c47dc7294a18ce58
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6165
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: grfn <grfn@gws.fyi>

2 files changed, 11 insertions, 10 deletions

diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index ecb819fad77c..0ab4538a4d8c 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -38,8 +38,8 @@ impl AttrsRep {
 
             AttrsRep::KV { name, value } => {
                 *self = AttrsRep::Map(BTreeMap::from([
-                    ("name".into(), std::mem::replace(name, Value::Blackhole)),
-                    ("value".into(), std::mem::replace(value, Value::Blackhole)),
+                    (NixString::NAME, std::mem::replace(name, Value::Blackhole)),
+                    (NixString::VALUE, std::mem::replace(value, Value::Blackhole)),
                 ]));
                 self.map_mut()
             }
@@ -62,7 +62,7 @@ impl AttrsRep {
                 None
             }
 
-            AttrsRep::Map(map) => map.get(&key.to_string().into()),
+            AttrsRep::Map(map) => map.get(&key.into()),
         }
     }
 }
diff --git a/tvix/eval/src/value/string.rs b/tvix/eval/src/value/string.rs
index 302566821881..626cf398f2dc 100644
--- a/tvix/eval/src/value/string.rs
+++ b/tvix/eval/src/value/string.rs
@@ -1,3 +1,4 @@
+use smol_str::SmolStr;
 use std::hash::Hash;
 use std::{borrow::Cow, fmt::Display};
 
@@ -6,7 +7,7 @@ use std::{borrow::Cow, fmt::Display};
 
 #[derive(Clone, Debug)]
 enum StringRepr {
-    Static(&'static str),
+    Smol(SmolStr),
     Heap(String),
 }
 
@@ -33,9 +34,9 @@ impl Ord for NixString {
     }
 }
 
-impl From<&'static str> for NixString {
-    fn from(s: &'static str) -> Self {
-        NixString(StringRepr::Static(s))
+impl From<&str> for NixString {
+    fn from(s: &str) -> Self {
+        NixString(StringRepr::Smol(SmolStr::new(s)))
     }
 }
 
@@ -52,12 +53,12 @@ impl Hash for NixString {
 }
 
 impl NixString {
-    pub const NAME: Self = NixString(StringRepr::Static("name"));
-    pub const VALUE: Self = NixString(StringRepr::Static("value"));
+    pub const NAME: Self = NixString(StringRepr::Smol(SmolStr::new_inline("name")));
+    pub const VALUE: Self = NixString(StringRepr::Smol(SmolStr::new_inline("value")));
 
     pub fn as_str(&self) -> &str {
         match &self.0 {
-            StringRepr::Static(s) => s,
+            StringRepr::Smol(s) => s.as_str(),
             StringRepr::Heap(s) => s,
         }
     }