feat(tvix/eval): Implement builtins.genList

Change-Id: Iabe28656229f508226b244d81382e517961eb3cf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6901
Autosubmit: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/eval/src/builtins/mod.rs

@@ -222,6 +222,17 @@ fn pure_builtins() -> Vec<Builtin> {
                 .map(|list| Value::List(NixList::from(list)))
                 .map_err(Into::into)
         }),
+        Builtin::new("genList", &[true, true], |args: Vec<Value>, vm: &mut VM| {
+            let len = args[1].as_int()?;
+            (0..len)
+                .map(|i| {
+                    vm.push(i.into());
+                    vm.call_value(&args[0])
+                })
+                .collect::<Result<Vec<Value>, _>>()
+                .map(|list| Value::List(NixList::from(list)))
+                .map_err(Into::into)
+        }),
         Builtin::new("getAttr", &[true, true], |args: Vec<Value>, _: &mut VM| {
             let k = args[0].to_str()?;
             let xs = args[1].to_attrs()?;

tvix/eval/src/tests/tvix_tests/eval-okay-genlist.exp

@@ -0,0 +1 @@
+[ 0 1 4 9 16 ]

tvix/eval/src/tests/tvix_tests/eval-okay-genlist.nix

@@ -0,0 +1 @@
+builtins.genList (x: x * x) 5

tvix/eval/src/value/mod.rs

@@ -359,6 +359,12 @@ impl Display for Value {
     }
 }
 
+impl From<i64> for Value {
+    fn from(i: i64) -> Self {
+        Self::Integer(i)
+    }
+}
+
 fn type_error(expected: &'static str, actual: &Value) -> ErrorKind {
     ErrorKind::TypeError {
         expected,