refactor(tvix/eval): introduce Closure struct in Value type r/4605

This struct will carry the upvalue machinery in addition to the lambda
itself. For now, all lambdas are wrapped in closures (though
technically analysis of the environment can later remove innermost
Closure wrapper, but this optimisation may not be worth it).

Change-Id: If2b68549ec1ea4ab838fdc47a2181c694ac937f2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6269
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

5 files changed, 17 insertions, 10 deletions

diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 11e0dc8d9fa7..99a63c97998d 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -44,7 +44,7 @@ fn pure_builtins() -> Vec<Builtin> {
         }),
         Builtin::new("isFunction", 1, |args| {
             Ok(Value::Bool(match args[0] {
-                Value::Lambda(_) => true,
+                Value::Closure(_) => true,
                 Value::Builtin(_) => true,
                 _ => false,
             }))
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index 5cb02a66b96a..3160c68c6e3c 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -23,7 +23,7 @@ use std::rc::Rc;
 use crate::chunk::Chunk;
 use crate::errors::{Error, ErrorKind, EvalResult};
 use crate::opcode::{CodeIdx, OpCode};
-use crate::value::{Lambda, Value};
+use crate::value::{Closure, Lambda, Value};
 use crate::warnings::{EvalWarning, WarningKind};
 
 /// Represents the result of compiling a piece of Nix code. If
@@ -822,7 +822,9 @@ impl Compiler {
             crate::disassembler::disassemble_chunk(&compiled.lambda.chunk);
         }
 
-        self.emit_constant(Value::Lambda(compiled.lambda));
+        self.emit_constant(Value::Closure(Closure {
+            lambda: compiled.lambda,
+        }));
     }
 
     fn compile_apply(&mut self, node: ast::Apply) {
diff --git a/tvix/eval/src/value/lambda.rs b/tvix/eval/src/value/function.rs
index d8609f50f367..45efc24f09f8 100644
--- a/tvix/eval/src/value/lambda.rs
+++ b/tvix/eval/src/value/function.rs
@@ -21,3 +21,8 @@ impl Lambda {
         &mut self.chunk
     }
 }
+
+#[derive(Clone, Debug)]
+pub struct Closure {
+    pub lambda: Lambda,
+}
diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs
index bf07c5d326d0..6bd1efde52ff 100644
--- a/tvix/eval/src/value/mod.rs
+++ b/tvix/eval/src/value/mod.rs
@@ -5,14 +5,14 @@ use std::{fmt::Display, path::PathBuf};
 
 mod attrs;
 mod builtin;
-mod lambda;
+mod function;
 mod list;
 mod string;
 
 use crate::errors::{ErrorKind, EvalResult};
 pub use attrs::NixAttrs;
 pub use builtin::Builtin;
-pub use lambda::Lambda;
+pub use function::{Closure, Lambda};
 pub use list::NixList;
 pub use string::NixString;
 
@@ -27,7 +27,7 @@ pub enum Value {
     Path(PathBuf),
     Attrs(Rc<NixAttrs>),
     List(NixList),
-    Lambda(Lambda),
+    Closure(Closure),
     Builtin(Builtin),
 
     // Internal values that, while they technically exist at runtime,
@@ -52,7 +52,7 @@ impl Value {
             Value::Path(_) => "path",
             Value::Attrs(_) => "set",
             Value::List(_) => "list",
-            Value::Lambda(_) | Value::Builtin(_) => "lambda",
+            Value::Closure(_) | Value::Builtin(_) => "lambda",
 
             // Internal types
             Value::AttrPath(_) | Value::Blackhole | Value::NotFound => "internal",
@@ -130,7 +130,7 @@ impl Display for Value {
             Value::Path(p) => p.display().fmt(f),
             Value::Attrs(attrs) => attrs.fmt(f),
             Value::List(list) => list.fmt(f),
-            Value::Lambda(_) => f.write_str("lambda"), // TODO: print position
+            Value::Closure(_) => f.write_str("lambda"), // TODO: print position
             Value::Builtin(builtin) => builtin.fmt(f),
 
             // Nix prints floats with a maximum precision of 5 digits
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 1e39792cd56f..6a7ebd5e64d2 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -7,7 +7,7 @@ use crate::{
     chunk::Chunk,
     errors::{ErrorKind, EvalResult},
     opcode::OpCode,
-    value::{Lambda, NixAttrs, NixList, Value},
+    value::{Closure, Lambda, NixAttrs, NixList, Value},
 };
 
 #[cfg(feature = "disassembler")]
@@ -357,7 +357,7 @@ impl VM {
                 OpCode::OpCall => {
                     let callable = self.pop();
                     match callable {
-                        Value::Lambda(lambda) => self.call(lambda, 1),
+                        Value::Closure(Closure { lambda }) => self.call(lambda, 1),
                         Value::Builtin(builtin) => {
                             let arg = self.pop();
                             let result = builtin.apply(arg)?;