feat(tvix/eval): `match` DO NOT propagate context r/7332

`match` silently ignore the input context and do not propagate
it and successful matches.

The why is unclear but nixpkgs does rely implicitly on this behavior
because dynamic attribute selection cannot be done with contextful
strings.

Change-Id: I5167fa9b2c2db8ecab0c2fb3e9895c9cfce6eeb2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10441
Autosubmit: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

1 files changed, 13 insertions, 6 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index deb0f84ccc..4cf9074fb8 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -3,7 +3,6 @@
 //! See //tvix/eval/docs/builtins.md for a some context on the
 //! available builtins in Nix.
 
-use crate::NixContext;
 use builtin_macros::builtins;
 use genawaiter::rc::Gen;
 use imbl::OrdMap;
@@ -23,8 +22,6 @@ use crate::{
     value::{CoercionKind, NixAttrs, NixList, NixString, Thunk, Value},
 };
 
-use crate::NixContextElement;
-
 use self::versions::{VersionPart, VersionPartsIter};
 
 mod to_xml;
@@ -79,7 +76,7 @@ pub async fn coerce_value_to_path(
 
 #[builtins]
 mod pure_builtins {
-    use crate::value::PointerEquality;
+    use crate::{value::PointerEquality, NixContext, NixContextElement};
 
     use super::*;
 
@@ -850,7 +847,7 @@ mod pure_builtins {
         if s.is_catchable() {
             return Ok(s);
         }
-        let s = s.to_str()?;
+        let s = s.to_contextful_str()?;
         let re = regex;
         if re.is_catchable() {
             return Ok(re);
@@ -861,7 +858,17 @@ mod pure_builtins {
             Some(caps) => Ok(Value::List(
                 caps.iter()
                     .skip(1)
-                    .map(|grp| grp.map(|g| Value::from(g.as_str())).unwrap_or(Value::Null))
+                    .map(|grp| {
+                        // Surprisingly, Nix does not propagate
+                        // the original context here.
+                        // Though, it accepts contextful strings as an argument.
+                        // An example of such behaviors in nixpkgs
+                        // can be observed in make-initrd.nix when it comes
+                        // to compressors which are matched over their full command
+                        // and then a compressor name will be extracted from that.
+                        grp.map(|g| Value::String(g.as_str().into()))
+                            .unwrap_or(Value::Null)
+                    })
                     .collect::<imbl::Vector<Value>>()
                     .into(),
             )),