5 files changed, 66 insertions, 37 deletions
diff --git a/tvix/eval/src/builtins/impure.rs b/tvix/eval/src/builtins/impure.rs
index 006cd9d7ac93..d4e7c4170364 100644
--- a/tvix/eval/src/builtins/impure.rs
+++ b/tvix/eval/src/builtins/impure.rs
@@ -12,7 +12,7 @@ use crate::{
     compiler::GlobalsMap,
     errors::ErrorKind,
     observer::NoOpObserver,
-    value::{Builtin, NixAttrs, Thunk},
+    value::{Builtin, BuiltinArgument, NixAttrs, Thunk},
     vm::VM,
     SourceCode, Value,
 };
@@ -111,7 +111,10 @@ pub fn builtins_import(globals: &Weak<GlobalsMap>, source: SourceCode) -> Builti
 
     Builtin::new(
         "import",
-        &[true],
+        &[BuiltinArgument {
+            strict: true,
+            name: "path",
+        }],
         move |mut args: Vec<Value>, vm: &mut VM| {
             let mut path = super::coerce_value_to_path(&args.pop().unwrap(), vm)?;
             if path.is_dir() {
diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index caa575fcf3bc..9b6e29db0a3d 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -5,6 +5,7 @@
 
 use crate::compiler::{GlobalsMap, GlobalsMapFunc};
 use crate::source::SourceCode;
+use crate::value::BuiltinArgument;
 use std::cmp::{self, Ordering};
 use std::collections::{BTreeMap, HashMap, HashSet};
 use std::path::PathBuf;
@@ -907,7 +908,16 @@ fn placeholders() -> Vec<Builtin> {
     vec![
         Builtin::new(
             "addErrorContext",
-            &[false, false],
+            &[
+                BuiltinArgument {
+                    strict: false,
+                    name: "context",
+                },
+                BuiltinArgument {
+                    strict: false,
+                    name: "value",
+                },
+            ],
             |mut args: Vec<Value>, vm: &mut VM| {
                 vm.emit_warning(WarningKind::NotImplemented("builtins.addErrorContext"));
                 Ok(args.pop().unwrap())
@@ -915,7 +925,10 @@ fn placeholders() -> Vec<Builtin> {
         ),
         Builtin::new(
             "unsafeDiscardStringContext",
-            &[true],
+            &[BuiltinArgument {
+                strict: true,
+                name: "s",
+            }],
             |mut args: Vec<Value>, vm: &mut VM| {
                 vm.emit_warning(WarningKind::NotImplemented(
                     "builtins.unsafeDiscardStringContext",
@@ -923,28 +936,35 @@ fn placeholders() -> Vec<Builtin> {
                 Ok(args.pop().unwrap())
             },
         ),
-        Builtin::new("derivation", &[true], |args: Vec<Value>, vm: &mut VM| {
-            vm.emit_warning(WarningKind::NotImplemented("builtins.derivation"));
-
-            // We do not implement derivations yet, so this function sets mock
-            // values on the fields that a real derivation would contain.
-            //
-            // Crucially this means we do not yet *validate* the values either.
-            let attrs = unwrap_or_clone_rc(args[0].to_attrs()?);
-            let attrs = attrs.update(NixAttrs::from_map(BTreeMap::from([
-                (
-                    "outPath".into(),
-                    "/nix/store/00000000000000000000000000000000-mock".into(),
-                ),
-                (
-                    "drvPath".into(),
-                    "/nix/store/00000000000000000000000000000000-mock.drv".into(),
-                ),
-                ("type".into(), "derivation".into()),
-            ])));
-
-            Ok(Value::Attrs(Rc::new(attrs)))
-        }),
+        Builtin::new(
+            "derivation",
+            &[BuiltinArgument {
+                strict: true,
+                name: "attrs",
+            }],
+            |args: Vec<Value>, vm: &mut VM| {
+                vm.emit_warning(WarningKind::NotImplemented("builtins.derivation"));
+
+                // We do not implement derivations yet, so this function sets mock
+                // values on the fields that a real derivation would contain.
+                //
+                // Crucially this means we do not yet *validate* the values either.
+                let attrs = unwrap_or_clone_rc(args[0].to_attrs()?);
+                let attrs = attrs.update(NixAttrs::from_map(BTreeMap::from([
+                    (
+                        "outPath".into(),
+                        "/nix/store/00000000000000000000000000000000-mock".into(),
+                    ),
+                    (
+                        "drvPath".into(),
+                        "/nix/store/00000000000000000000000000000000-mock.drv".into(),
+                    ),
+                    ("type".into(), "derivation".into()),
+                ])));
+
+                Ok(Value::Attrs(Rc::new(attrs)))
+            },
+        ),
     ]
 }
 // we set TVIX_CURRENT_SYSTEM in build.rs
diff --git a/tvix/eval/src/lib.rs b/tvix/eval/src/lib.rs
index 106f7d851cd3..3e160fa92cf6 100644
--- a/tvix/eval/src/lib.rs
+++ b/tvix/eval/src/lib.rs
@@ -37,7 +37,7 @@ pub use crate::vm::run_lambda;
 /// Internal-only parts of `tvix-eval`, exported for use in macros, but not part of the public
 /// interface of the crate.
 pub mod internal {
-    pub use crate::value::Builtin;
+    pub use crate::value::{Builtin, BuiltinArgument};
     pub use crate::vm::VM;
 }
 
diff --git a/tvix/eval/src/value/builtin.rs b/tvix/eval/src/value/builtin.rs
index fc8043176211..944efd85eb99 100644
--- a/tvix/eval/src/value/builtin.rs
+++ b/tvix/eval/src/value/builtin.rs
@@ -25,6 +25,14 @@ use std::{
 pub trait BuiltinFn: Fn(Vec<Value>, &mut VM) -> Result<Value, ErrorKind> {}
 impl<F: Fn(Vec<Value>, &mut VM) -> Result<Value, ErrorKind>> BuiltinFn for F {}
 
+/// Description of a single argument passed to a builtin
+pub struct BuiltinArgument {
+    /// Whether the argument should be forced before the underlying builtin function is called
+    pub strict: bool,
+    /// The name of the argument, to be used in docstrings and error messages
+    pub name: &'static str,
+}
+
 /// Represents a single built-in function which directly executes Rust
 /// code that operates on a Nix value.
 ///
@@ -40,10 +48,8 @@ impl<F: Fn(Vec<Value>, &mut VM) -> Result<Value, ErrorKind>> BuiltinFn for F {}
 #[derive(Clone)]
 pub struct Builtin {
     name: &'static str,
-    /// Array reference that describes how many arguments there are (usually 1
-    /// or 2) and whether they need to be forced. `true` causes the
-    /// corresponding argument to be forced before `func` is called.
-    strict_args: &'static [bool],
+    /// Array of arguments to the builtin.
+    arguments: &'static [BuiltinArgument],
     func: Rc<dyn BuiltinFn>,
 
     /// Partially applied function arguments.
@@ -53,12 +59,12 @@ pub struct Builtin {
 impl Builtin {
     pub fn new<F: BuiltinFn + 'static>(
         name: &'static str,
-        strict_args: &'static [bool],
+        arguments: &'static [BuiltinArgument],
         func: F,
     ) -> Self {
         Builtin {
             name,
-            strict_args,
+            arguments,
             func: Rc::new(func),
             partials: vec![],
         }
@@ -74,9 +80,9 @@ impl Builtin {
     pub fn apply(mut self, vm: &mut VM, arg: Value) -> Result<Value, ErrorKind> {
         self.partials.push(arg);
 
-        if self.partials.len() == self.strict_args.len() {
-            for (idx, force) in self.strict_args.iter().enumerate() {
-                if *force {
+        if self.partials.len() == self.arguments.len() {
+            for (idx, BuiltinArgument { strict, .. }) in self.arguments.iter().enumerate() {
+                if *strict {
                     self.partials[idx].force(vm)?;
                 }
             }
diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs
index db72081e8dcf..f0bb3628d831 100644
--- a/tvix/eval/src/value/mod.rs
+++ b/tvix/eval/src/value/mod.rs
@@ -20,7 +20,7 @@ use crate::errors::ErrorKind;
 use crate::opcode::StackIdx;
 use crate::vm::VM;
 pub use attrs::NixAttrs;
-pub use builtin::Builtin;
+pub use builtin::{Builtin, BuiltinArgument};
 pub(crate) use function::Formals;
 pub use function::{Closure, Lambda};
 pub use list::NixList;