refactor(tvix/eval): Upgrade to latest rnix-parser r/4567

Since the latest published version of rnix-parser on crates.io, the
crate has undergone major changes which are only available in the git
repository at the moment. This commit updates the compiler to this
newer version of rnix.

Most notably, the entire AST provided by rnix is now wrapped in the
AST type system. As a result of this traversal is much nicer in many
places, especially for things like nested attribute selection.

There are a handful of smaller features missing for full feature
parity with the previous version, especially handling of path
literals, but PRs for these already exist in rnix-parser.

Change-Id: Icde6d393067976549492b7d89c4cc49e5e575fc7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6231
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

6 files changed, 382 insertions, 490 deletions

diff --git a/tvix/eval/Cargo.lock b/tvix/eval/Cargo.lock
index 59381377bb7b..e64e5e8ce0bc 100644
--- a/tvix/eval/Cargo.lock
+++ b/tvix/eval/Cargo.lock
@@ -50,15 +50,6 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "37b2a672a2cb129a2e41c10b1224bb368f9f37a2b16b612598138befd7b37eb5"
 
 [[package]]
-name = "cbitset"
-version = "0.2.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29b6ad25ae296159fb0da12b970b2fe179b234584d7cd294c891e2bbb284466b"
-dependencies = [
- "num-traits",
-]
-
-[[package]]
 name = "cc"
 version = "1.0.73"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -94,9 +85,9 @@ dependencies = [
 
 [[package]]
 name = "countme"
-version = "2.0.4"
+version = "3.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "328b822bdcba4d4e402be8d9adb6eebf269f969f8eadef977a553ff3c4fbcb58"
+checksum = "7704b5fdd17b18ae31c4c1da5a2e0305a2bf17b5249300a9ee9ed7b72114c636"
 
 [[package]]
 name = "criterion"
@@ -337,9 +328,9 @@ checksum = "eabb4a44450da02c90444cf74558da904edde8fb4e9035a9a6a4e15445af0bd7"
 
 [[package]]
 name = "hashbrown"
-version = "0.9.1"
+version = "0.12.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d7afe4a420e3fe79967a00898cc1f4db7c8a49a9333a29f8a4bd76a253d5cd04"
+checksum = "8a9ee70c43aaf417c914396645a0fa852624801b24ebb7ae78fe8272889ac888"
 
 [[package]]
 name = "hermit-abi"
@@ -647,20 +638,17 @@ checksum = "a3f87b73ce11b1619a3c6332f45341e0047173771e8b8b73f87bfeefb7b56244"
 
 [[package]]
 name = "rnix"
-version = "0.10.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8024a523e8836f1a5d051203dc00d833357fee94e351b51348dfaeca5364daa9"
+version = "0.11.0-dev"
+source = "git+https://github.com/nix-community/rnix-parser.git?rev=ae9fe1344993bb57d292f361c83e0379282e88ed#ae9fe1344993bb57d292f361c83e0379282e88ed"
 dependencies = [
- "cbitset",
  "rowan",
- "smol_str",
 ]
 
 [[package]]
 name = "rowan"
-version = "0.12.6"
+version = "0.15.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a1b36e449f3702f3b0c821411db1cbdf30fb451726a9456dce5dabcd44420043"
+checksum = "e88acf7b001007e9e8c989fe7449f6601d909e5dd2c56399fc158977ad6c56e8"
 dependencies = [
  "countme",
  "hashbrown",
@@ -735,9 +723,9 @@ checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
 [[package]]
 name = "serde"
-version = "1.0.142"
+version = "1.0.144"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e590c437916fb6b221e1d00df6e3294f3fccd70ca7e92541c475d6ed6ef5fee2"
+checksum = "0f747710de3dcd43b88c9168773254e809d8ddbdf9653b84e2554ab219f17860"
 
 [[package]]
 name = "serde_cbor"
@@ -852,18 +840,18 @@ dependencies = [
 
 [[package]]
 name = "thiserror"
-version = "1.0.32"
+version = "1.0.33"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f5f6586b7f764adc0231f4c79be7b920e766bb2f3e51b3661cdb263828f19994"
+checksum = "3d0a539a918745651435ac7db7a18761589a94cd7e94cd56999f828bf73c8a57"
 dependencies = [
  "thiserror-impl",
 ]
 
 [[package]]
 name = "thiserror-impl"
-version = "1.0.32"
+version = "1.0.33"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "12bafc5b54507e0149cdf1b145a5d80ab80a90bcd9275df43d4fff68460f6c21"
+checksum = "c251e90f708e16c49a16f4917dc2131e75222b72edfa9cb7f7c58ae56aae0c09"
 dependencies = [
  "proc-macro2 1.0.43",
  "quote 1.0.21",
@@ -889,6 +877,7 @@ dependencies = [
  "path-clean",
  "pretty_assertions",
  "rnix",
+ "rowan",
  "rustyline",
  "smol_str",
  "tabwriter",
diff --git a/tvix/eval/Cargo.toml b/tvix/eval/Cargo.toml
index 0416171c3689..7a35dedfce86 100644
--- a/tvix/eval/Cargo.toml
+++ b/tvix/eval/Cargo.toml
@@ -6,12 +6,18 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-rnix = "0.10.2"
 smol_str = "0.1"
 rustyline = "10.0.0"
 dirs = "4.0.0"
 path-clean = "0.1"
 tabwriter = { version = "1.2", optional = true }
+rowan = "*" # pinned by rnix
+
+# rnix has not been released in a while (as of 2022-08-16), we will
+# use it from git.
+[dependencies.rnix]
+git = "https://github.com/nix-community/rnix-parser.git"
+rev = "ae9fe1344993bb57d292f361c83e0379282e88ed"
 
 [dev-dependencies]
 criterion = "0.3.6"
diff --git a/tvix/eval/src/compiler.rs b/tvix/eval/src/compiler.rs
index 27e917c54569..dca4eec9f447 100644
--- a/tvix/eval/src/compiler.rs
+++ b/tvix/eval/src/compiler.rs
@@ -14,7 +14,8 @@
 //! mistakes early during development.
 
 use path_clean::PathClean;
-use rnix::types::{BinOpKind, EntryHolder, TokenWrapper, TypedNode, Wrapper};
+use rnix::ast::{self, AstToken, HasEntry};
+use rowan::ast::AstNode;
 use std::path::{Path, PathBuf};
 
 use crate::chunk::Chunk;
@@ -90,164 +91,85 @@ struct Compiler {
 }
 
 impl Compiler {
-    fn compile(&mut self, node: rnix::SyntaxNode) -> EvalResult<()> {
-        match node.kind() {
-            // Root of a file contains no content, it's just a marker
-            // type.
-            rnix::SyntaxKind::NODE_ROOT => self.compile(node.first_child().expect("TODO")),
-
-            // Literals contain a single token consisting of the
-            // literal itself.
-            rnix::SyntaxKind::NODE_LITERAL => {
-                let value = rnix::types::Value::cast(node).unwrap();
-                self.compile_literal(value)
-            }
-
-            rnix::SyntaxKind::NODE_STRING => {
-                let op = rnix::types::Str::cast(node).unwrap();
-                self.compile_string(op)
-            }
-
-            // The interpolation & dynamic nodes are just wrappers
-            // around the inner value of a fragment, they only require
-            // unwrapping.
-            rnix::SyntaxKind::NODE_STRING_INTERPOL | rnix::SyntaxKind::NODE_DYNAMIC => {
-                self.compile(node.first_child().expect("TODO (should not be possible)"))
-            }
-
-            rnix::SyntaxKind::NODE_BIN_OP => {
-                let op = rnix::types::BinOp::cast(node).expect("TODO (should not be possible)");
-                self.compile_binop(op)
-            }
-
-            rnix::SyntaxKind::NODE_UNARY_OP => {
-                let op = rnix::types::UnaryOp::cast(node).expect("TODO: (should not be possible)");
-                self.compile_unary_op(op)
-            }
-
-            rnix::SyntaxKind::NODE_PAREN => {
-                let node = rnix::types::Paren::cast(node).unwrap();
-                self.compile(node.inner().unwrap())
-            }
-
-            rnix::SyntaxKind::NODE_IDENT => {
-                let node = rnix::types::Ident::cast(node).unwrap();
-                self.compile_ident(node)
-            }
-
-            rnix::SyntaxKind::NODE_ATTR_SET => {
-                let node = rnix::types::AttrSet::cast(node).unwrap();
-                self.compile_attr_set(node)
-            }
-
-            rnix::SyntaxKind::NODE_SELECT => {
-                let node = rnix::types::Select::cast(node).unwrap();
-                self.compile_select(node)
-            }
-
-            rnix::SyntaxKind::NODE_OR_DEFAULT => {
-                let node = rnix::types::OrDefault::cast(node).unwrap();
-                self.compile_or_default(node)
-            }
-
-            rnix::SyntaxKind::NODE_LIST => {
-                let node = rnix::types::List::cast(node).unwrap();
-                self.compile_list(node)
-            }
-
-            rnix::SyntaxKind::NODE_IF_ELSE => {
-                let node = rnix::types::IfElse::cast(node).unwrap();
-                self.compile_if_else(node)
-            }
-
-            rnix::SyntaxKind::NODE_LET_IN => {
-                let node = rnix::types::LetIn::cast(node).unwrap();
-                self.compile_let_in(node)
-            }
-
-            rnix::SyntaxKind::NODE_WITH => {
-                let node = rnix::types::With::cast(node).unwrap();
-                self.compile_with(node)
-            }
-
-            rnix::SyntaxKind::NODE_ASSERT => {
-                let node = rnix::types::Assert::cast(node).unwrap();
-                self.compile_assert(node)
-            }
-
-            kind => panic!("visiting unsupported node: {:?}", kind),
+    fn compile(&mut self, expr: ast::Expr) -> EvalResult<()> {
+        match expr {
+            ast::Expr::Literal(literal) => self.compile_literal(literal),
+            ast::Expr::Path(path) => self.compile_path(path),
+            ast::Expr::Str(s) => self.compile_str(s),
+            ast::Expr::UnaryOp(op) => self.compile_unary_op(op),
+            ast::Expr::BinOp(op) => self.compile_binop(op),
+            ast::Expr::HasAttr(has_attr) => self.compile_has_attr(has_attr),
+            ast::Expr::List(list) => self.compile_list(list),
+            ast::Expr::AttrSet(attrs) => self.compile_attr_set(attrs),
+            ast::Expr::Select(select) => self.compile_select(select),
+            ast::Expr::Assert(assert) => self.compile_assert(assert),
+            ast::Expr::IfElse(if_else) => self.compile_if_else(if_else),
+            ast::Expr::LetIn(let_in) => self.compile_let_in(let_in),
+            ast::Expr::Ident(ident) => self.compile_ident(ident),
+            ast::Expr::With(with) => self.compile_with(with),
+
+            // Parenthesized expressions are simply unwrapped, leaving
+            // their value on the stack.
+            ast::Expr::Paren(paren) => self.compile(paren.expr().unwrap()),
+
+            ast::Expr::LegacyLet(_) => todo!("legacy let"),
+            ast::Expr::Lambda(_) => todo!("function definition"),
+            ast::Expr::Apply(_) => todo!("function application"),
+
+            ast::Expr::Root(_) => unreachable!("there cannot be more than one root"),
+            ast::Expr::Error(_) => unreachable!("compile is only called on validated trees"),
         }
     }
 
-    /// Compiles nodes the same way that `Self::compile` does, with
-    /// the exception of identifiers which are added literally to the
-    /// stack as string values.
-    ///
-    /// This is needed for correctly accessing attribute sets.
-    fn compile_with_literal_ident(&mut self, node: rnix::SyntaxNode) -> EvalResult<()> {
-        if node.kind() == rnix::SyntaxKind::NODE_IDENT {
-            let ident = rnix::types::Ident::cast(node).unwrap();
-            self.emit_literal_ident(&ident);
-            return Ok(());
-        }
-
-        self.compile(node)
-    }
-
-    fn compile_literal(&mut self, node: rnix::types::Value) -> EvalResult<()> {
-        match node.to_value().unwrap() {
-            rnix::NixValue::Float(f) => {
-                let idx = self.chunk.push_constant(Value::Float(f));
+    fn compile_literal(&mut self, node: ast::Literal) -> EvalResult<()> {
+        match node.kind() {
+            ast::LiteralKind::Float(f) => {
+                let idx = self.chunk.push_constant(Value::Float(f.value().unwrap()));
                 self.chunk.push_op(OpCode::OpConstant(idx));
                 Ok(())
             }
 
-            rnix::NixValue::Integer(i) => {
-                let idx = self.chunk.push_constant(Value::Integer(i));
+            ast::LiteralKind::Integer(i) => {
+                let idx = self.chunk.push_constant(Value::Integer(i.value().unwrap()));
                 self.chunk.push_op(OpCode::OpConstant(idx));
                 Ok(())
             }
-
-            // These nodes are yielded by literal URL values.
-            rnix::NixValue::String(s) => {
+            ast::LiteralKind::Uri(u) => {
                 self.warnings.push(EvalWarning {
-                    node: node.node().clone(),
+                    node: node.syntax().clone(),
                     kind: WarningKind::DeprecatedLiteralURL,
                 });
 
-                let idx = self.chunk.push_constant(Value::String(s.into()));
+                let idx = self
+                    .chunk
+                    .push_constant(Value::String(u.syntax().text().into()));
                 self.chunk.push_op(OpCode::OpConstant(idx));
                 Ok(())
             }
-
-            rnix::NixValue::Path(anchor, path) => self.compile_path(anchor, path),
         }
     }
 
-    fn compile_path(&mut self, anchor: rnix::value::Anchor, path: String) -> EvalResult<()> {
-        let path = match anchor {
-            rnix::value::Anchor::Absolute => Path::new(&path).to_owned(),
-
-            rnix::value::Anchor::Home => {
-                let mut buf = dirs::home_dir().ok_or_else(|| {
-                    Error::PathResolution("failed to determine home directory".into())
-                })?;
-
-                buf.push(&path);
-                buf
-            }
-
-            rnix::value::Anchor::Relative => {
-                let mut buf = self.root_dir.clone();
-                buf.push(path);
-                buf
-            }
-
-            // This confusingly named variant is actually
-            // angle-bracket lookups, which in C++ Nix desugar
-            // to calls to `__findFile` (implicitly in the
-            // current scope).
-            rnix::value::Anchor::Store => todo!("resolve <...> lookups at runtime"),
+    fn compile_path(&mut self, node: ast::Path) -> EvalResult<()> {
+        // TODO(tazjin): placeholder implementation while waiting for
+        // https://github.com/nix-community/rnix-parser/pull/96
+
+        let raw_path = node.to_string();
+        let path = if raw_path.starts_with('/') {
+            Path::new(&raw_path).to_owned()
+        } else if raw_path.starts_with('~') {
+            let mut buf = dirs::home_dir().ok_or_else(|| {
+                Error::PathResolution("failed to determine home directory".into())
+            })?;
+
+            buf.push(&raw_path);
+            buf
+        } else if raw_path.starts_with('.') {
+            let mut buf = self.root_dir.clone();
+            buf.push(&raw_path);
+            buf
+        } else {
+            // TODO: decide what to do with findFile
+            todo!("other path types (e.g. <...> lookups) not yet implemented")
         };
 
         // TODO: Use https://github.com/rust-lang/rfcs/issues/2208
@@ -259,23 +181,23 @@ impl Compiler {
         Ok(())
     }
 
-    fn compile_string(&mut self, string: rnix::types::Str) -> EvalResult<()> {
+    fn compile_str(&mut self, node: ast::Str) -> EvalResult<()> {
         let mut count = 0;
 
         // The string parts are produced in literal order, however
         // they need to be reversed on the stack in order to
         // efficiently create the real string in case of
         // interpolation.
-        for part in string.parts().into_iter().rev() {
+        for part in node.parts().into_iter().rev() {
             count += 1;
 
             match part {
                 // Interpolated expressions are compiled as normal and
                 // dealt with by the VM before being assembled into
                 // the final string.
-                rnix::StrPart::Ast(node) => self.compile(node)?,
+                ast::StrPart::Interpolation(node) => self.compile(node.expr().unwrap())?,
 
-                rnix::StrPart::Literal(lit) => {
+                ast::StrPart::Literal(lit) => {
                     let idx = self.chunk.push_constant(Value::String(lit.into()));
                     self.chunk.push_op(OpCode::OpConstant(idx));
                 }
@@ -289,20 +211,36 @@ impl Compiler {
         Ok(())
     }
 
-    fn compile_binop(&mut self, op: rnix::types::BinOp) -> EvalResult<()> {
+    fn compile_unary_op(&mut self, op: ast::UnaryOp) -> EvalResult<()> {
+        self.compile(op.expr().unwrap())?;
+
+        let opcode = match op.operator().unwrap() {
+            ast::UnaryOpKind::Invert => OpCode::OpInvert,
+            ast::UnaryOpKind::Negate => OpCode::OpNegate,
+        };
+
+        self.chunk.push_op(opcode);
+        Ok(())
+    }
+
+    fn compile_binop(&mut self, op: ast::BinOp) -> EvalResult<()> {
+        use ast::BinOpKind;
+
         // Short-circuiting and other strange operators, which are
         // under the same node type as NODE_BIN_OP, but need to be
         // handled separately (i.e. before compiling the expressions
         // used for standard binary operators).
+
         match op.operator().unwrap() {
             BinOpKind::And => return self.compile_and(op),
             BinOpKind::Or => return self.compile_or(op),
             BinOpKind::Implication => return self.compile_implication(op),
-            BinOpKind::IsSet => return self.compile_is_set(op),
-
             _ => {}
         };
 
+        // For all other operators, the two values need to be left on
+        // the stack in the correct order before pushing the
+        // instruction for the operation itself.
         self.compile(op.lhs().unwrap())?;
         self.compile(op.rhs().unwrap())?;
 
@@ -325,7 +263,7 @@ impl Compiler {
             }
 
             // Handled by separate branch above.
-            BinOpKind::And | BinOpKind::Implication | BinOpKind::Or | BinOpKind::IsSet => {
+            BinOpKind::And | BinOpKind::Implication | BinOpKind::Or => {
                 unreachable!()
             }
         };
@@ -333,58 +271,125 @@ impl Compiler {
         Ok(())
     }
 
-    fn compile_unary_op(&mut self, op: rnix::types::UnaryOp) -> EvalResult<()> {
-        self.compile(op.value().unwrap())?;
+    fn compile_and(&mut self, node: ast::BinOp) -> EvalResult<()> {
+        debug_assert!(
+            matches!(node.operator(), Some(ast::BinOpKind::And)),
+            "compile_and called with wrong operator kind: {:?}",
+            node.operator(),
+        );
 
-        use rnix::types::UnaryOpKind;
-        let opcode = match op.operator() {
-            UnaryOpKind::Invert => OpCode::OpInvert,
-            UnaryOpKind::Negate => OpCode::OpNegate,
-        };
+        // Leave left-hand side value on the stack.
+        self.compile(node.lhs().unwrap())?;
+
+        // If this value is false, jump over the right-hand side - the
+        // whole expression is false.
+        let end_idx = self.chunk.push_op(OpCode::OpJumpIfFalse(0));
+
+        // Otherwise, remove the previous value and leave the
+        // right-hand side on the stack. Its result is now the value
+        // of the whole expression.
+        self.chunk.push_op(OpCode::OpPop);
+        self.compile(node.rhs().unwrap())?;
+
+        self.patch_jump(end_idx);
+        self.chunk.push_op(OpCode::OpAssertBool);
 
-        self.chunk.push_op(opcode);
         Ok(())
     }
 
-    fn compile_ident(&mut self, node: rnix::types::Ident) -> EvalResult<()> {
-        match node.as_str() {
-            // TODO(tazjin): Nix technically allows code like
-            //
-            //   let null = 1; in null
-            //   => 1
-            //
-            // which we do *not* want to check at runtime. Once
-            // scoping is introduced, the compiler should carry some
-            // optimised information about any "weird" stuff that's
-            // happened to the scope (such as overrides of these
-            // literals, or builtins).
-            "true" if self.scope.poisoned_true == 0 => self.chunk.push_op(OpCode::OpTrue),
-            "false" if self.scope.poisoned_false == 0 => self.chunk.push_op(OpCode::OpFalse),
-            "null" if self.scope.poisoned_null == 0 => self.chunk.push_op(OpCode::OpNull),
+    fn compile_or(&mut self, node: ast::BinOp) -> EvalResult<()> {
+        debug_assert!(
+            matches!(node.operator(), Some(ast::BinOpKind::Or)),
+            "compile_or called with wrong operator kind: {:?}",
+            node.operator(),
+        );
 
-            name => {
-                // Note: `with` and some other special scoping
-                // features are not yet implemented.
-                match self.resolve_local(name) {
-                    Some(idx) => self.chunk.push_op(OpCode::OpGetLocal(idx)),
-                    None => {
-                        if self.scope.with_stack.is_empty() {
-                            return Err(Error::UnknownStaticVariable(node));
-                        }
+        // Leave left-hand side value on the stack
+        self.compile(node.lhs().unwrap())?;
 
-                        // Variable needs to be dynamically resolved
-                        // at runtime.
-                        let idx = self.chunk.push_constant(Value::String(name.into()));
-                        self.chunk.push_op(OpCode::OpConstant(idx));
-                        self.chunk.push_op(OpCode::OpResolveWith)
-                    }
-                }
+        // Opposite of above: If this value is **true**, we can
+        // short-circuit the right-hand side.
+        let end_idx = self.chunk.push_op(OpCode::OpJumpIfTrue(0));
+        self.chunk.push_op(OpCode::OpPop);
+        self.compile(node.rhs().unwrap())?;
+        self.patch_jump(end_idx);
+        self.chunk.push_op(OpCode::OpAssertBool);
+
+        Ok(())
+    }
+
+    fn compile_implication(&mut self, node: ast::BinOp) -> EvalResult<()> {
+        debug_assert!(
+            matches!(node.operator(), Some(ast::BinOpKind::Implication)),
+            "compile_implication called with wrong operator kind: {:?}",
+            node.operator(),
+        );
+
+        // Leave left-hand side value on the stack and invert it.
+        self.compile(node.lhs().unwrap())?;
+        self.chunk.push_op(OpCode::OpInvert);
+
+        // Exactly as `||` (because `a -> b` = `!a || b`).
+        let end_idx = self.chunk.push_op(OpCode::OpJumpIfTrue(0));
+        self.chunk.push_op(OpCode::OpPop);
+        self.compile(node.rhs().unwrap())?;
+        self.patch_jump(end_idx);
+        self.chunk.push_op(OpCode::OpAssertBool);
+
+        Ok(())
+    }
+
+    fn compile_has_attr(&mut self, node: ast::HasAttr) -> EvalResult<()> {
+        // Put the attribute set on the stack.
+        self.compile(node.expr().unwrap())?;
+        let mut count = 0;
+
+        // Push all path fragments with an operation for fetching the
+        // next nested element, for all fragments except the last one.
+        for fragment in node.attrpath().unwrap().attrs() {
+            if count > 0 {
+                self.chunk.push_op(OpCode::OpAttrOrNotFound);
             }
-        };
+            count += 1;
+            self.compile_attr(fragment)?;
+        }
+
+        // After the last fragment, emit the actual instruction that
+        // leaves a boolean on the stack.
+        self.chunk.push_op(OpCode::OpAttrsIsSet);
 
         Ok(())
     }
 
+    fn compile_attr(&mut self, node: ast::Attr) -> EvalResult<()> {
+        match node {
+            ast::Attr::Dynamic(dynamic) => self.compile(dynamic.expr().unwrap()),
+            ast::Attr::Str(s) => self.compile_str(s),
+            ast::Attr::Ident(ident) => {
+                self.emit_literal_ident(&ident);
+                Ok(())
+            }
+        }
+    }
+
+    // Compile list literals into equivalent bytecode. List
+    // construction is fairly simple, consisting of pushing code for
+    // each literal element and an instruction with the element count.
+    //
+    // The VM, after evaluating the code for each element, simply
+    // constructs the list from the given number of elements.
+    fn compile_list(&mut self, node: ast::List) -> EvalResult<()> {
+        let mut count = 0;
+
+        for item in node.items() {
+            count += 1;
+            self.compile(item)?;
+        }
+
+        self.chunk.push_op(OpCode::OpList(count));
+        Ok(())
+    }
+
     // Compile attribute set literals into equivalent bytecode.
     //
     // This is complicated by a number of features specific to Nix
@@ -393,8 +398,8 @@ impl Compiler {
     // 1. Keys can be dynamically constructed through interpolation.
     // 2. Keys can refer to nested attribute sets.
     // 3. Attribute sets can (optionally) be recursive.
-    fn compile_attr_set(&mut self, node: rnix::types::AttrSet) -> EvalResult<()> {
-        if node.recursive() {
+    fn compile_attr_set(&mut self, node: ast::AttrSet) -> EvalResult<()> {
+        if node.rec_token().is_some() {
             todo!("recursive attribute sets are not yet implemented")
         }
 
@@ -420,7 +425,7 @@ impl Compiler {
                         // instruction followed by a merge, rather
                         // than pushing/popping the same attrs
                         // potentially a lot of times.
-                        self.compile(from.inner().unwrap())?;
+                        self.compile(from.expr().unwrap())?;
                         self.emit_literal_ident(&ident);
                         self.chunk.push_op(OpCode::OpAttrsSelect);
                     }
@@ -431,7 +436,7 @@ impl Compiler {
                         count += 1;
                         self.emit_literal_ident(&ident);
 
-                        match self.resolve_local(ident.as_str()) {
+                        match self.resolve_local(ident.ident_token().unwrap().text()) {
                             Some(idx) => self.chunk.push_op(OpCode::OpGetLocal(idx)),
                             None => return Err(Error::UnknownStaticVariable(ident)),
                         };
@@ -440,7 +445,7 @@ impl Compiler {
             }
         }
 
-        for kv in node.entries() {
+        for kv in node.attrpath_values() {
             count += 1;
 
             // Because attribute set literals can contain nested keys,
@@ -449,26 +454,9 @@ impl Compiler {
             // runtime value representing the attribute path is
             // emitted.
             let mut key_count = 0;
-            for fragment in kv.key().unwrap().path() {
+            for fragment in kv.attrpath().unwrap().attrs() {
                 key_count += 1;
-
-                match fragment.kind() {
-                    rnix::SyntaxKind::NODE_IDENT => {
-                        let ident = rnix::types::Ident::cast(fragment).unwrap();
-
-                        // TODO(tazjin): intern!
-                        let idx = self
-                            .chunk
-                            .push_constant(Value::String(ident.as_str().into()));
-                        self.chunk.push_op(OpCode::OpConstant(idx));
-                    }
-
-                    // For all other expression types, we simply
-                    // compile them as normal. The operation should
-                    // result in a string value, which is checked at
-                    // runtime on construction.
-                    _ => self.compile(fragment)?,
-                }
+                self.compile_attr(fragment)?;
             }
 
             // We're done with the key if there was only one fragment,
@@ -488,175 +476,24 @@ impl Compiler {
         Ok(())
     }
 
-    fn compile_select(&mut self, node: rnix::types::Select) -> EvalResult<()> {
-        // Push the set onto the stack
-        self.compile(node.set().unwrap())?;
-
-        // Push the key and emit the access instruction.
-        //
-        // This order matters because the key needs to be evaluated
-        // first to fail in the correct order on type errors.
-        self.compile_with_literal_ident(node.index().unwrap())?;
-        self.chunk.push_op(OpCode::OpAttrsSelect);
+    fn compile_select(&mut self, node: ast::Select) -> EvalResult<()> {
+        let set = node.expr().unwrap();
+        let path = node.attrpath().unwrap();
 
-        Ok(())
-    }
-
-    // Compile list literals into equivalent bytecode. List
-    // construction is fairly simple, consisting of pushing code for
-    // each literal element and an instruction with the element count.
-    //
-    // The VM, after evaluating the code for each element, simply
-    // constructs the list from the given number of elements.
-    fn compile_list(&mut self, node: rnix::types::List) -> EvalResult<()> {
-        let mut count = 0;
-
-        for item in node.items() {
-            count += 1;
-            self.compile(item)?;
+        if node.or_token().is_some() {
+            return self.compile_select_or(set, path, node.default_expr().unwrap());
         }
 
-        self.chunk.push_op(OpCode::OpList(count));
-        Ok(())
-    }
-
-    // Compile conditional expressions using jumping instructions in the VM.
-    //
-    //                        ┌────────────────────┐
-    //                        │ 0  [ conditional ] │
-    //                        │ 1   JUMP_IF_FALSE →┼─┐
-    //                        │ 2  [  main body  ] │ │ Jump to else body if
-    //                       ┌┼─3─←     JUMP       │ │ condition is false.
-    //  Jump over else body  ││ 4  [  else body  ]←┼─┘
-    //  if condition is true.└┼─5─→     ...        │
-    //                        └────────────────────┘
-    fn compile_if_else(&mut self, node: rnix::types::IfElse) -> EvalResult<()> {
-        self.compile(node.condition().unwrap())?;
-
-        let then_idx = self.chunk.push_op(OpCode::OpJumpIfFalse(0));
-
-        self.chunk.push_op(OpCode::OpPop); // discard condition value
-        self.compile(node.body().unwrap())?;
-
-        let else_idx = self.chunk.push_op(OpCode::OpJump(0));
-
-        self.patch_jump(then_idx); // patch jump *to* else_body
-        self.chunk.push_op(OpCode::OpPop); // discard condition value
-        self.compile(node.else_body().unwrap())?;
-
-        self.patch_jump(else_idx); // patch jump *over* else body
-
-        Ok(())
-    }
-
-    fn compile_and(&mut self, node: rnix::types::BinOp) -> EvalResult<()> {
-        debug_assert!(
-            matches!(node.operator(), Some(BinOpKind::And)),
-            "compile_and called with wrong operator kind: {:?}",
-            node.operator(),
-        );
-
-        // Leave left-hand side value on the stack.
-        self.compile(node.lhs().unwrap())?;
-
-        // If this value is false, jump over the right-hand side - the
-        // whole expression is false.
-        let end_idx = self.chunk.push_op(OpCode::OpJumpIfFalse(0));
-
-        // Otherwise, remove the previous value and leave the
-        // right-hand side on the stack. Its result is now the value
-        // of the whole expression.
-        self.chunk.push_op(OpCode::OpPop);
-        self.compile(node.rhs().unwrap())?;
-
-        self.patch_jump(end_idx);
-        self.chunk.push_op(OpCode::OpAssertBool);
-
-        Ok(())
-    }
-
-    fn compile_or(&mut self, node: rnix::types::BinOp) -> EvalResult<()> {
-        debug_assert!(
-            matches!(node.operator(), Some(BinOpKind::Or)),
-            "compile_or called with wrong operator kind: {:?}",
-            node.operator(),
-        );
-
-        // Leave left-hand side value on the stack
-        self.compile(node.lhs().unwrap())?;
-
-        // Opposite of above: If this value is **true**, we can
-        // short-circuit the right-hand side.
-        let end_idx = self.chunk.push_op(OpCode::OpJumpIfTrue(0));
-        self.chunk.push_op(OpCode::OpPop);
-        self.compile(node.rhs().unwrap())?;
-        self.patch_jump(end_idx);
-        self.chunk.push_op(OpCode::OpAssertBool);
-
-        Ok(())
-    }
-
-    fn compile_implication(&mut self, node: rnix::types::BinOp) -> EvalResult<()> {
-        debug_assert!(
-            matches!(node.operator(), Some(BinOpKind::Implication)),
-            "compile_implication called with wrong operator kind: {:?}",
-            node.operator(),
-        );
-
-        // Leave left-hand side value on the stack and invert it.
-        self.compile(node.lhs().unwrap())?;
-        self.chunk.push_op(OpCode::OpInvert);
-
-        // Exactly as `||` (because `a -> b` = `!a || b`).
-        let end_idx = self.chunk.push_op(OpCode::OpJumpIfTrue(0));
-        self.chunk.push_op(OpCode::OpPop);
-        self.compile(node.rhs().unwrap())?;
-        self.patch_jump(end_idx);
-        self.chunk.push_op(OpCode::OpAssertBool);
-
-        Ok(())
-    }
-
-    fn compile_is_set(&mut self, node: rnix::types::BinOp) -> EvalResult<()> {
-        debug_assert!(
-            matches!(node.operator(), Some(BinOpKind::IsSet)),
-            "compile_is_set called with wrong operator kind: {:?}",
-            node.operator(),
-        );
-
-        // Put the attribute set on the stack.
-        self.compile(node.lhs().unwrap())?;
+        // Push the set onto the stack
+        self.compile(set)?;
 
-        // If the key is a NODE_SELECT, the check is deeper than one
-        // level and requires special handling.
+        // Compile each key fragment and emit access instructions.
         //
-        // Otherwise, the right hand side is the (only) key expression
-        // itself and can be compiled directly.
-        let mut next = node.rhs().unwrap();
-        let mut fragments = vec![];
-
-        loop {
-            if matches!(next.kind(), rnix::SyntaxKind::NODE_SELECT) {
-                // Keep nesting deeper until we encounter something
-                // different than `NODE_SELECT` on the left side. This is
-                // required because `rnix` parses nested keys as select
-                // expressions, instead of as a key expression.
-                //
-                // The parsed tree will nest something like `a.b.c.d.e.f`
-                // as (((((a, b), c), d), e), f).
-                fragments.push(next.last_child().unwrap());
-                next = next.first_child().unwrap();
-            } else {
-                self.compile_with_literal_ident(next)?;
-
-                for fragment in fragments.into_iter().rev() {
-                    self.chunk.push_op(OpCode::OpAttrOrNotFound);
-                    self.compile_with_literal_ident(fragment)?;
-                }
-
-                self.chunk.push_op(OpCode::OpAttrsIsSet);
-                break;
-            }
+        // TODO: multi-select instruction to avoid re-pushing attrs on
+        // nested selects.
+        for fragment in path.attrs() {
+            self.compile_attr(fragment)?;
+            self.chunk.push_op(OpCode::OpAttrsSelect);
         }
 
         Ok(())
@@ -691,50 +528,81 @@ impl Compiler {
     ///  │ 14 ...                     │   │ ..   ....               │
     ///  └────────────────────────────┘   └─────────────────────────┘
     /// ```
-    fn compile_or_default(&mut self, node: rnix::types::OrDefault) -> EvalResult<()> {
-        let select = node.index().unwrap();
-
-        let mut next = select.set().unwrap();
-        let mut fragments = vec![select.index().unwrap()];
+    fn compile_select_or(
+        &mut self,
+        set: ast::Expr,
+        path: ast::Attrpath,
+        default: ast::Expr,
+    ) -> EvalResult<()> {
+        self.compile(set)?;
         let mut jumps = vec![];
 
-        loop {
-            if matches!(next.kind(), rnix::SyntaxKind::NODE_SELECT) {
-                fragments.push(next.last_child().unwrap());
-                next = next.first_child().unwrap();
-                continue;
-            } else {
-                self.compile(next)?;
-            }
-
-            for fragment in fragments.into_iter().rev() {
-                self.compile_with_literal_ident(fragment)?;
-                self.chunk.push_op(OpCode::OpAttrOrNotFound);
-                jumps.push(self.chunk.push_op(OpCode::OpJumpIfNotFound(0)));
-            }
-
-            break;
+        for fragment in path.attrs() {
+            self.compile_attr(fragment)?;
+            self.chunk.push_op(OpCode::OpAttrOrNotFound);
+            jumps.push(self.chunk.push_op(OpCode::OpJumpIfNotFound(0)));
         }
 
         let final_jump = self.chunk.push_op(OpCode::OpJump(0));
+
         for jump in jumps {
             self.patch_jump(jump);
         }
 
         // Compile the default value expression and patch the final
         // jump to point *beyond* it.
-        self.compile(node.default().unwrap())?;
+        self.compile(default)?;
         self.patch_jump(final_jump);
 
         Ok(())
     }
 
+    fn compile_assert(&mut self, node: ast::Assert) -> EvalResult<()> {
+        // Compile the assertion condition to leave its value on the stack.
+        self.compile(node.condition().unwrap())?;
+        self.chunk.push_op(OpCode::OpAssert);
+
+        // The runtime will abort evaluation at this point if the
+        // assertion failed, if not the body simply continues on like
+        // normal.
+        self.compile(node.body().unwrap())
+    }
+
+    // Compile conditional expressions using jumping instructions in the VM.
+    //
+    //                        ┌────────────────────┐
+    //                        │ 0  [ conditional ] │
+    //                        │ 1   JUMP_IF_FALSE →┼─┐
+    //                        │ 2  [  main body  ] │ │ Jump to else body if
+    //                       ┌┼─3─←     JUMP       │ │ condition is false.
+    //  Jump over else body  ││ 4  [  else body  ]←┼─┘
+    //  if condition is true.└┼─5─→     ...        │
+    //                        └────────────────────┘
+    fn compile_if_else(&mut self, node: ast::IfElse) -> EvalResult<()> {
+        self.compile(node.condition().unwrap())?;
+
+        let then_idx = self.chunk.push_op(OpCode::OpJumpIfFalse(0));
+
+        self.chunk.push_op(OpCode::OpPop); // discard condition value
+        self.compile(node.body().unwrap())?;
+
+        let else_idx = self.chunk.push_op(OpCode::OpJump(0));
+
+        self.patch_jump(then_idx); // patch jump *to* else_body
+        self.chunk.push_op(OpCode::OpPop); // discard condition value
+        self.compile(node.else_body().unwrap())?;
+
+        self.patch_jump(else_idx); // patch jump *over* else body
+
+        Ok(())
+    }
+
     // Compile a standard `let ...; in ...` statement.
     //
     // Unless in a non-standard scope, the encountered values are
     // simply pushed on the stack and their indices noted in the
     // entries vector.
-    fn compile_let_in(&mut self, node: rnix::types::LetIn) -> EvalResult<()> {
+    fn compile_let_in(&mut self, node: ast::LetIn) -> EvalResult<()> {
         self.begin_scope();
 
         for inherit in node.inherits() {
@@ -743,7 +611,7 @@ impl Compiler {
                 // scope is practically a no-op.
                 None => {
                     self.warnings.push(EvalWarning {
-                        node: inherit.node().clone(),
+                        node: inherit.syntax().clone(),
                         kind: WarningKind::UselessInherit,
                     });
 
@@ -752,19 +620,17 @@ impl Compiler {
 
                 Some(from) => {
                     for ident in inherit.idents() {
-                        // TODO: Optimised multi-select instruction?
-                        self.compile(from.inner().unwrap())?;
+                        self.compile(from.expr().unwrap())?;
                         self.emit_literal_ident(&ident);
                         self.chunk.push_op(OpCode::OpAttrsSelect);
-                        self.declare_local(ident.as_str());
+                        self.declare_local(ident.ident_token().unwrap().text());
                     }
                 }
             }
         }
 
-        for entry in node.entries() {
-            let key = entry.key().unwrap();
-            let mut path = normalise_ident_path(key.path())?;
+        for entry in node.attrpath_values() {
+            let mut path = normalise_ident_path(entry.attrpath().unwrap().attrs())?;
 
             if path.len() != 1 {
                 todo!("nested bindings in let expressions :(")
@@ -780,10 +646,49 @@ impl Compiler {
         Ok(())
     }
 
+    fn compile_ident(&mut self, node: ast::Ident) -> EvalResult<()> {
+        match node.ident_token().unwrap().text() {
+            // TODO(tazjin): Nix technically allows code like
+            //
+            //   let null = 1; in null
+            //   => 1
+            //
+            // which we do *not* want to check at runtime. Once
+            // scoping is introduced, the compiler should carry some
+            // optimised information about any "weird" stuff that's
+            // happened to the scope (such as overrides of these
+            // literals, or builtins).
+            "true" if self.scope.poisoned_true == 0 => self.chunk.push_op(OpCode::OpTrue),
+            "false" if self.scope.poisoned_false == 0 => self.chunk.push_op(OpCode::OpFalse),
+            "null" if self.scope.poisoned_null == 0 => self.chunk.push_op(OpCode::OpNull),
+
+            name => {
+                // Note: `with` and some other special scoping
+                // features are not yet implemented.
+                match self.resolve_local(name) {
+                    Some(idx) => self.chunk.push_op(OpCode::OpGetLocal(idx)),
+                    None => {
+                        if self.scope.with_stack.is_empty() {
+                            return Err(Error::UnknownStaticVariable(node));
+                        }
+
+                        // Variable needs to be dynamically resolved
+                        // at runtime.
+                        let idx = self.chunk.push_constant(Value::String(name.into()));
+                        self.chunk.push_op(OpCode::OpConstant(idx));
+                        self.chunk.push_op(OpCode::OpResolveWith)
+                    }
+                }
+            }
+        };
+
+        Ok(())
+    }
+
     // Compile `with` expressions by emitting instructions that
     // pop/remove the indices of attribute sets that are implicitly in
     // scope through `with` on the "with-stack".
-    fn compile_with(&mut self, node: rnix::types::With) -> EvalResult<()> {
+    fn compile_with(&mut self, node: ast::With) -> EvalResult<()> {
         // TODO: Detect if the namespace is just an identifier, and
         // resolve that directly (thus avoiding duplication on the
         // stack).
@@ -800,24 +705,14 @@ impl Compiler {
         self.compile(node.body().unwrap())
     }
 
-    fn compile_assert(&mut self, node: rnix::types::Assert) -> EvalResult<()> {
-        // Compile the assertion condition to leave its value on the stack.
-        self.compile(node.condition().unwrap())?;
-        self.chunk.push_op(OpCode::OpAssert);
-
-        // The runtime will abort evaluation at this point if the
-        // assertion failed, if not the body simply continues on like
-        // normal.
-        self.compile(node.body().unwrap())
-    }
-
-    // Emit the literal string value of an identifier. Required for
-    // several operations related to attribute sets, where identifiers
-    // are used as string keys.
-    fn emit_literal_ident(&mut self, ident: &rnix::types::Ident) {
+    /// Emit the literal string value of an identifier. Required for
+    /// several operations related to attribute sets, where
+    /// identifiers are used as string keys.
+    fn emit_literal_ident(&mut self, ident: &ast::Ident) {
         let idx = self
             .chunk
-            .push_constant(Value::String(ident.as_str().into()));
+            .push_constant(Value::String(ident.ident_token().unwrap().text().into()));
+
         self.chunk.push_op(OpCode::OpConstant(idx));
     }
 
@@ -934,48 +829,44 @@ impl Compiler {
     }
 }
 
-/// Convert a single identifier path fragment to a string if possible,
-/// or raise an error about the node being dynamic.
-fn ident_fragment_to_string(node: rnix::SyntaxNode) -> EvalResult<String> {
-    match node.kind() {
-        rnix::SyntaxKind::NODE_IDENT => {
-            Ok(rnix::types::Ident::cast(node).unwrap().as_str().to_string())
-        }
-
-        rnix::SyntaxKind::NODE_STRING => {
-            let s = rnix::types::Str::cast(node).unwrap();
-            let mut parts = s.parts();
-
-            if parts.len() == 1 {
-                if let rnix::value::StrPart::Literal(lit) = parts.pop().unwrap() {
-                    return Ok(lit);
-                }
-            }
-
-            return Err(Error::DynamicKeyInLet(s.node().clone()));
+/// Convert a non-dynamic string expression to a string if possible,
+/// or raise an error.
+fn expr_str_to_string(expr: ast::Str) -> EvalResult<String> {
+    if expr.parts().len() == 1 {
+        if let ast::StrPart::Literal(s) = expr.parts().pop().unwrap() {
+            return Ok(s);
         }
+    }
 
-        // The dynamic node type is just a wrapper and we recurse to
-        // its inner node. C++ Nix does not care about the dynamic
-        // wrapper when determining whether the node itself is
-        // dynamic, it depends solely on the expression inside (i.e.
-        // `let ${"a"} = 1; in a` is valid)
-        rnix::SyntaxKind::NODE_DYNAMIC => {
-            ident_fragment_to_string(rnix::types::Dynamic::cast(node).unwrap().inner().unwrap())
-        }
+    return Err(Error::DynamicKeyInLet(expr.syntax().clone()));
+}
 
-        _ => Err(Error::DynamicKeyInLet(node)),
+/// Convert a single identifier path fragment to a string if possible,
+/// or raise an error about the node being dynamic.
+fn attr_to_string(node: ast::Attr) -> EvalResult<String> {
+    match node {
+        ast::Attr::Ident(ident) => Ok(ident.ident_token().unwrap().text().into()),
+        ast::Attr::Str(s) => expr_str_to_string(s),
+
+        // The dynamic node type is just a wrapper. C++ Nix does not
+        // care about the dynamic wrapper when determining whether the
+        // node itself is dynamic, it depends solely on the expression
+        // inside (i.e. `let ${"a"} = 1; in a` is valid).
+        ast::Attr::Dynamic(ref dynamic) => match dynamic.expr().unwrap() {
+            ast::Expr::Str(s) => expr_str_to_string(s),
+            _ => Err(Error::DynamicKeyInLet(node.syntax().clone())),
+        },
     }
 }
 
 // Normalises identifier fragments into a single string vector for
 // `let`-expressions; fails if fragments requiring dynamic computation
 // are encountered.
-fn normalise_ident_path<I: Iterator<Item = rnix::SyntaxNode>>(path: I) -> EvalResult<Vec<String>> {
-    path.map(ident_fragment_to_string).collect()
+fn normalise_ident_path<I: Iterator<Item = ast::Attr>>(path: I) -> EvalResult<Vec<String>> {
+    path.map(attr_to_string).collect()
 }
 
-pub fn compile(ast: rnix::AST, location: Option<PathBuf>) -> EvalResult<CompilationResult> {
+pub fn compile(expr: ast::Expr, location: Option<PathBuf>) -> EvalResult<CompilationResult> {
     let mut root_dir = match location {
         Some(dir) => Ok(dir),
         None => std::env::current_dir().map_err(|e| {
@@ -997,7 +888,7 @@ pub fn compile(ast: rnix::AST, location: Option<PathBuf>) -> EvalResult<Compilat
         scope: Default::default(),
     };
 
-    c.compile(ast.node())?;
+    c.compile(expr)?;
 
     Ok(CompilationResult {
         chunk: c.chunk,
diff --git a/tvix/eval/src/errors.rs b/tvix/eval/src/errors.rs
index 03f22306ec35..4aba877f4979 100644
--- a/tvix/eval/src/errors.rs
+++ b/tvix/eval/src/errors.rs
@@ -27,7 +27,7 @@ pub enum Error {
     DynamicKeyInLet(rnix::SyntaxNode),
 
     // Unknown variable in statically known scope.
-    UnknownStaticVariable(rnix::types::Ident),
+    UnknownStaticVariable(rnix::ast::Ident),
 
     // Unknown variable in dynamic scope (with, rec, ...).
     UnknownDynamicVariable(String),
diff --git a/tvix/eval/src/eval.rs b/tvix/eval/src/eval.rs
index 94290af5376d..cd11d3289b12 100644
--- a/tvix/eval/src/eval.rs
+++ b/tvix/eval/src/eval.rs
@@ -1,6 +1,6 @@
 use std::path::PathBuf;
 
-use rnix::{self, types::TypedNode};
+use rnix;
 
 use crate::{
     errors::{Error, EvalResult},
@@ -8,21 +8,27 @@ use crate::{
 };
 
 pub fn interpret(code: &str, location: Option<PathBuf>) -> EvalResult<Value> {
-    let ast = rnix::parse(code);
+    let parsed = rnix::ast::Root::parse(code);
+    let errors = parsed.errors();
 
-    let errors = ast.errors();
     if !errors.is_empty() {
-        for err in &errors {
+        for err in errors {
             eprintln!("parse error: {}", err);
-            return Err(Error::ParseErrors(errors));
         }
+        return Err(Error::ParseErrors(errors.to_vec()));
     }
 
+    // If we've reached this point, there are no errors.
+    let root_expr = parsed
+        .tree()
+        .expr()
+        .expect("expression should exist if no errors occured");
+
     if std::env::var("TVIX_DISPLAY_AST").is_ok() {
-        println!("{}", ast.root().dump());
+        println!("{:?}", root_expr);
     }
 
-    let result = crate::compiler::compile(ast, location)?;
+    let result = crate::compiler::compile(root_expr, location)?;
 
     #[cfg(feature = "disassembler")]
     crate::disassembler::disassemble_chunk(&result.chunk);
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index e088d22776db..cf70fda30747 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -83,7 +83,7 @@ impl VM {
     }
 
     fn pop(&mut self) -> Value {
-        self.stack.pop().expect("TODO")
+        self.stack.pop().expect("runtime stack empty")
     }
 
     fn push(&mut self, value: Value) {