fix(tvix/eval): make sure to deref thunk in type predicate builtins r/4936

Previously we only matched the outer constructor after forcing which
would mean that we would always return `false` if the inspected value
was a thunk, regardless what value would be present inside.

Change-Id: I361ea6e855e23ef8e5b59098a50b9cd59253803f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6692
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

3 files changed, 63 insertions, 18 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 18a50f255a..dfc1986141 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -154,35 +154,45 @@ fn pure_builtins() -> Vec<Builtin> {
             Some(x) => Ok(x.clone()),
             None => Err(ErrorKind::IndexOutOfBounds { index: 0 }),
         }),
-        Builtin::new("isAttrs", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::Attrs(_))))
+        // For `is*` predicates we force manually, as Value::force also unwraps any Thunks
+        Builtin::new("isAttrs", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::Attrs(_))))
         }),
-        Builtin::new("isBool", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::Bool(_))))
+        Builtin::new("isBool", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::Bool(_))))
         }),
-        Builtin::new("isFloat", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::Float(_))))
+        Builtin::new("isFloat", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::Float(_))))
         }),
-        Builtin::new("isFunction", &[true], |args, _| {
+        Builtin::new("isFunction", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
             Ok(Value::Bool(matches!(
-                args[0],
+                *value,
                 Value::Closure(_) | Value::Builtin(_)
             )))
         }),
-        Builtin::new("isInt", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::Integer(_))))
+        Builtin::new("isInt", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::Integer(_))))
         }),
-        Builtin::new("isList", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::List(_))))
+        Builtin::new("isList", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::List(_))))
         }),
-        Builtin::new("isNull", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::Null)))
+        Builtin::new("isNull", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::Null)))
         }),
-        Builtin::new("isPath", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::Path(_))))
+        Builtin::new("isPath", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::Path(_))))
         }),
-        Builtin::new("isString", &[true], |args, _| {
-            Ok(Value::Bool(matches!(args[0], Value::String(_))))
+        Builtin::new("isString", &[false], |args, vm| {
+            let value = args[0].force(vm)?;
+            Ok(Value::Bool(matches!(*value, Value::String(_))))
         }),
         Builtin::new("mul", &[true, true], |mut args, _| {
             let b = args.pop().unwrap();
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-type-predicates.exp b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-type-predicates.exp
new file mode 100644
index 0000000000..724c1f9c34
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-type-predicates.exp
@@ -0,0 +1 @@
+[ true true false true true false true true false true true false true true false true true false true true false true true false true true true false ]
diff --git a/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-type-predicates.nix b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-type-predicates.nix
new file mode 100644
index 0000000000..3d688cb8bd
--- /dev/null
+++ b/tvix/eval/src/tests/tvix_tests/eval-okay-builtins-type-predicates.nix
@@ -0,0 +1,34 @@
+let
+  # apply is thunked, so we can create a thunked value using the identity function
+  thunk = x: x;
+in
+[
+  (builtins.isAttrs { bar = throw "baz"; })
+  (builtins.isAttrs (thunk { foo = 13; }))
+  (builtins.isAttrs (thunk 123))
+  (builtins.isBool true)
+  (builtins.isBool (thunk false))
+  (builtins.isBool (thunk "lol"))
+  (builtins.isFloat 1.2)
+  (builtins.isFloat (thunk (1 * 1.0)))
+  (builtins.isFloat 1)
+  (builtins.isFunction thunk)
+  (builtins.isFunction (thunk thunk))
+  (builtins.isFunction {})
+  (builtins.isInt 1)
+  (builtins.isInt (thunk 42))
+  (builtins.isInt 1.0)
+  (builtins.isList [ (throw "oh no") (abort "it's over") ])
+  (builtins.isList (thunk [ 21 21 ]))
+  (builtins.isList (thunk {}))
+  (builtins.isNull null)
+  (builtins.isNull (thunk null))
+  (builtins.isNull 42)
+  (builtins.isPath ./relative)
+  (builtins.isPath (thunk /absolute))
+  (builtins.isPath "/not/a/path")
+  (builtins.isString "simple")
+  (builtins.isString "${{ outPath = "coerced"; }}")
+  (builtins.isString "hello ${"interpolation"}")
+  (builtins.isString true)
+]