fix(tvix): Catch errors for generator in some builtins r/7487

Nix doesn't propagate errors for the function argument to some builtins,
like genList and map:

    ❯ nix repl
    Welcome to Nix version 2.3.17. Type :? for help.

    nix-repl> (builtins.tryEval (builtins.genList (builtins.throw "a") 10)).success
    true

    nix-repl> (builtins.tryEval (builtins.map (builtins.throw "a") [ "" ])).success
    true

Note that this is untested as of this particular commit, only because a
big test suite covering all sorts of catchable error propagation issues
is coming next

Change-Id: I48c8eb390a541204b1a6d438c753fa1ca9b3877e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10753
Autosubmit: aspen <root@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

1 files changed, 3 insertions, 2 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index a3b32e9e02..716da4d041 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -524,7 +524,8 @@ mod pure_builtins {
     #[builtin("genList")]
     async fn builtin_gen_list(
         co: GenCo,
-        generator: Value,
+        // Nix 2.3 doesn't propagate failures here
+        #[catch] generator: Value,
         length: Value,
     ) -> Result<Value, ErrorKind> {
         let mut out = imbl::Vector::<Value>::new();
@@ -911,7 +912,7 @@ mod pure_builtins {
     }
 
     #[builtin("map")]
-    async fn builtin_map(co: GenCo, f: Value, list: Value) -> Result<Value, ErrorKind> {
+    async fn builtin_map(co: GenCo, #[catch] f: Value, list: Value) -> Result<Value, ErrorKind> {
         let mut out = imbl::Vector::<Value>::new();
 
         // the best span we can get…