fix(tvix/eval): don't force lambda arg in map, mapAttrs & genList r/7735

It is pretty pointless to force the function argument if we are going to
use a suspended call later since forcing the function may fail in ways
that are not covered by Catchables (non-recoverable errors, infinite
recursions). From this, it kind of seems as if using #[catch] is never
correct and should be replaced by #[lazy]. Also we should probably try
to come up with more test cases for stuff where laziness gets us out of
the jam as an equivalent to the catchable tests for nonrecoverable
errors.

Fixes b/386.

Change-Id: Ia926df4ac1b440ec430403ab7b40924a0c97221b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11153
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Autosubmit: sterni <sternenseemann@systemli.org>

8 files changed, 38 insertions, 4 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index a2136ee6ad05..b19ba7009f2f 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -523,7 +523,7 @@ mod pure_builtins {
     async fn builtin_gen_list(
         co: GenCo,
         // Nix 2.3 doesn't propagate failures here
-        #[catch] generator: Value,
+        #[lazy] generator: Value,
         length: Value,
     ) -> Result<Value, ErrorKind> {
         let mut out = imbl::Vector::<Value>::new();
@@ -905,7 +905,7 @@ mod pure_builtins {
     }
 
     #[builtin("map")]
-    async fn builtin_map(co: GenCo, #[catch] f: Value, list: Value) -> Result<Value, ErrorKind> {
+    async fn builtin_map(co: GenCo, #[lazy] f: Value, list: Value) -> Result<Value, ErrorKind> {
         let mut out = imbl::Vector::<Value>::new();
 
         // the best span we can get…
@@ -920,7 +920,11 @@ mod pure_builtins {
     }
 
     #[builtin("mapAttrs")]
-    async fn builtin_map_attrs(co: GenCo, f: Value, attrs: Value) -> Result<Value, ErrorKind> {
+    async fn builtin_map_attrs(
+        co: GenCo,
+        #[lazy] f: Value,
+        attrs: Value,
+    ) -> Result<Value, ErrorKind> {
         let attrs = attrs.to_attrs()?;
         let mut out = imbl::OrdMap::new();
 
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genList-function-strictness.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genList-function-strictness.exp
new file mode 100644
index 000000000000..06712ebc33e4
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genList-function-strictness.exp
@@ -0,0 +1 @@
+[ <LAMBDA> 0 1 2 ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genList-function-strictness.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genList-function-strictness.nix
new file mode 100644
index 000000000000..e161e3b4af4f
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-genList-function-strictness.nix
@@ -0,0 +1,8 @@
+let
+  self =
+    let
+      l = builtins.genList (builtins.head self) 3;
+    in
+    [ (x: x) ] ++ l;
+in
+self
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map-function-strictness.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map-function-strictness.exp
new file mode 100644
index 000000000000..050c2c4de51f
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map-function-strictness.exp
@@ -0,0 +1 @@
+[ <LAMBDA> 2 "." 18 "https://github.com/NixOS/nix/issues/9779" "-.-" ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map-function-strictness.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map-function-strictness.nix
new file mode 100644
index 000000000000..932d3d0eaebc
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-map-function-strictness.nix
@@ -0,0 +1,8 @@
+let
+  self =
+    let
+      l = builtins.map (builtins.head self) [ 2 "." 18 https://github.com/NixOS/nix/issues/9779 "-.-" ];
+    in
+    [ (x: x) ] ++ l;
+in
+self
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-mapAttrs-function-strictness.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-mapAttrs-function-strictness.exp
new file mode 100644
index 000000000000..7e70748ffd6f
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-mapAttrs-function-strictness.exp
@@ -0,0 +1 @@
+{ a = 1; b = 2; f = <LAMBDA>; }
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-mapAttrs-function-strictness.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-mapAttrs-function-strictness.nix
new file mode 100644
index 000000000000..2946d6de1760
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-mapAttrs-function-strictness.nix
@@ -0,0 +1,8 @@
+let
+  self =
+    let
+      s = builtins.mapAttrs self.f { a = 1; b = 2; };
+    in
+    { f = _: x: x; } // s;
+in
+self
diff --git a/tvix/verify-lang-tests/default.nix b/tvix/verify-lang-tests/default.nix
index 276a57f12935..772c1c532078 100644
--- a/tvix/verify-lang-tests/default.nix
+++ b/tvix/verify-lang-tests/default.nix
@@ -76,11 +76,14 @@ let
     # b72bc4a972fe568744d98b89d63adcd504cb586c
     "eval-okay-identifier-formatting.nix" = [ nix ];
 
-    # Different catchable behavior between nix 2.3 and 2.18
+    # Differing strictness in the function argument for some builtins in Nix 2.18
+    # https://github.com/NixOS/nix/issues/9779
     "eval-okay-builtins-map-propagate-catchable.nix" = [ nix_latest ];
     "eval-okay-builtins-gen-list-propagate-catchable.nix" = [ nix_latest ];
     "eval-okay-builtins-replace-strings-propagate-catchable.nix" =
       [ nix_latest ];
+    "eval-okay-builtins-map-function-strictness.nix" = [ nix_latest ];
+    "eval-okay-builtins-genList-function-strictness.nix" = [ nix_latest ];
 
     # TODO(sterni): support diffing working directory and home relative paths
     # like C++ Nix test suite (using string replacement).