test(tvix/eval): genericClosure (pointer) comparison support r/6309

genericClosure has very limited support for pointer equality: It relies
on comparison (not equality!) in C++ Nix, so as soon as C++ Nix supports
comparing lists (langVersion >= 6) we can rely on pointer equality for
key.

Since Tvix uses equality, not comparison for the insert, our behavior is
currently different, as documented by the notyetpassing tests.

Change-Id: Ifcd741ed4fc3ccc3825f7038875d56a9918b786a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8720
Tested-by: BuildkiteCI
Autosubmit: sterni <sternenseemann@systemli.org>
Reviewed-by: tazjin <tazjin@tvl.su>

4 files changed, 37 insertions, 0 deletions

diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genericClosure-pointer-equality.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genericClosure-pointer-equality.exp
new file mode 100644
index 000000000000..87977137a57b
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genericClosure-pointer-equality.exp
@@ -0,0 +1 @@
+[ { key = [ { foo = <LAMBDA>; } ]; val = null; } ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genericClosure-pointer-equality.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genericClosure-pointer-equality.nix
new file mode 100644
index 000000000000..5e662cdaf75e
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genericClosure-pointer-equality.nix
@@ -0,0 +1,15 @@
+let
+  foo = x: x;
+in
+
+# key needs to be a list since it uses comparison, not equality checks:
+# lists are comparable in Nix if all non-comparable items in them are equal (e.g.
+# functions, attribute sets).
+builtins.genericClosure {
+  startSet = [
+    { key = [ { inherit foo; } ]; val = null; }
+  ];
+  operator = { val, ... }: if val != null then [] else [
+    { key = [ { inherit foo; } ]; val = throw "no pointer equality? 🥺👉👈"; }
+  ];
+}
diff --git a/tvix/eval/src/tests/tvix_tests/notyetpassing/eval-fail-builtins-genericClosure-uncomparable-keys.nix b/tvix/eval/src/tests/tvix_tests/notyetpassing/eval-fail-builtins-genericClosure-uncomparable-keys.nix
new file mode 100644
index 000000000000..d4e93e1f28c0
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/notyetpassing/eval-fail-builtins-genericClosure-uncomparable-keys.nix
@@ -0,0 +1,9 @@
+# Attribute sets can't be compared, only checked for equality
+builtins.genericClosure {
+  startSet = [
+    { key = { foo = 21; }; }
+  ];
+  operator = _: [
+    { key = { bar = 21; }; }
+  ];
+}
diff --git a/tvix/eval/src/tests/tvix_tests/notyetpassing/eval-fail-builtins-genericClosure-uncomparable-keys2.nix b/tvix/eval/src/tests/tvix_tests/notyetpassing/eval-fail-builtins-genericClosure-uncomparable-keys2.nix
new file mode 100644
index 000000000000..ca2825524546
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/notyetpassing/eval-fail-builtins-genericClosure-uncomparable-keys2.nix
@@ -0,0 +1,12 @@
+let
+  id = x: x;
+in
+
+builtins.genericClosure {
+  startSet = [ { key = id; first = true; } ];
+  operator =
+    { first, ... }:
+    if first then [
+      { key = id; first = false; }
+    ] else [];
+}