feat(tvix/eval): Implement builtins.intersectAttrs r/5137

Change-Id: Iaba9bcfa19f283cd0c1931be2f211e2528a1a940
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6998
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: kanepyork <rikingcoding@gmail.com>

3 files changed, 19 insertions, 0 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 0082d36d57..03466af65f 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -309,6 +309,21 @@ fn pure_builtins() -> Vec<Builtin> {
                 None => Err(ErrorKind::IndexOutOfBounds { index: 0 }),
             }
         }),
+        Builtin::new(
+            "intersectAttrs",
+            &[true, true],
+            |args: Vec<Value>, _: &mut VM| {
+                let mut res = BTreeMap::new();
+                let attrs1 = args[0].to_attrs()?;
+                let attrs2 = args[1].to_attrs()?;
+                for (k, v) in attrs2.iter() {
+                    if attrs1.contains(k) {
+                        res.insert(k.clone(), v.clone());
+                    }
+                }
+                Ok(Value::attrs(NixAttrs::from_map(res)))
+            },
+        ),
         // For `is*` predicates we force manually, as Value::force also unwraps any Thunks
         Builtin::new("isAttrs", &[false], |args: Vec<Value>, vm: &mut VM| {
             let value = args[0].force(vm)?;
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-intersectattrs.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-intersectattrs.exp
new file mode 100644
index 0000000000..25001b211f
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-intersectattrs.exp
@@ -0,0 +1 @@
+{ a = 100; b = 200; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-intersectattrs.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-intersectattrs.nix
new file mode 100644
index 0000000000..3534132ed4
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-intersectattrs.nix
@@ -0,0 +1,3 @@
+builtins.intersectAttrs
+  { a = 1; b = 2; c = 3; }
+  { a = 100; b = 200; d = 5; }