refactor(tvix/eval): Builderize Evaluation

Make constructing of a new Evaluation use the builder pattern rather
than setting public mutable fields. This is currently a pure
refactor (no functionality has changed) but has a few advantages:

- We've encapsulated the internals of the fields in Evaluation, meaning
  we can change them without too much breakage of clients
- We have type safety that prevents us from ever changing the fields of
  an Evaluation after it's built (which matters more in a world where we
  reuse Evaluations).

More importantly, this paves the road for doing different things with
the construction of an Evaluation - notably, sharing certain things like
the GlobalsMap across subsequent evaluations in eg the REPL.

Fixes: b/262
Change-Id: I4a27116faac14cdd144fc7c992d14ae095a1aca4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11956
Tested-by: BuildkiteCI
Autosubmit: aspen <root@gws.fyi>
Reviewed-by: flokli <flokli@flokli.de>

tvix/glue/src/builtins/mod.rs

@@ -18,13 +18,14 @@ pub use errors::{DerivationError, FetcherError, ImportError};
 ///
 /// As they need to interact with `known_paths`, we also need to pass in
 /// `known_paths`.
-pub fn add_derivation_builtins<IO>(eval: &mut tvix_eval::Evaluation<IO>, io: Rc<TvixStoreIO>) {
-    eval.builtins
-        .extend(derivation::derivation_builtins::builtins(Rc::clone(&io)));
-
-    // Add the actual `builtins.derivation` from compiled Nix code
-    eval.src_builtins
-        .push(("derivation", include_str!("derivation.nix")));
+pub fn add_derivation_builtins<'co, 'ro, 'env, IO>(
+    eval_builder: tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO>,
+    io: Rc<TvixStoreIO>,
+) -> tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO> {
+    eval_builder
+        .add_builtins(derivation::derivation_builtins::builtins(Rc::clone(&io)))
+        // Add the actual `builtins.derivation` from compiled Nix code
+        .add_src_builtin("derivation", include_str!("derivation.nix"))
 }
 
 /// Adds fetcher builtins to the passed [tvix_eval::Evaluation]:
@@ -32,9 +33,11 @@ pub fn add_derivation_builtins<IO>(eval: &mut tvix_eval::Evaluation<IO>, io: Rc<
 /// * `fetchurl`
 /// * `fetchTarball`
 /// * `fetchGit`
-pub fn add_fetcher_builtins<IO>(eval: &mut tvix_eval::Evaluation<IO>, io: Rc<TvixStoreIO>) {
-    eval.builtins
-        .extend(fetchers::fetcher_builtins::builtins(Rc::clone(&io)));
+pub fn add_fetcher_builtins<'co, 'ro, 'env, IO>(
+    eval_builder: tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO>,
+    io: Rc<TvixStoreIO>,
+) -> tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO> {
+    eval_builder.add_builtins(fetchers::fetcher_builtins::builtins(Rc::clone(&io)))
 }
 
 /// Adds import-related builtins to the passed [tvix_eval::Evaluation].
@@ -42,10 +45,12 @@ pub fn add_fetcher_builtins<IO>(eval: &mut tvix_eval::Evaluation<IO>, io: Rc<Tvi
 /// These are `filterSource` and `path`
 ///
 /// As they need to interact with the store implementation, we pass [`TvixStoreIO`].
-pub fn add_import_builtins<IO>(eval: &mut tvix_eval::Evaluation<IO>, io: Rc<TvixStoreIO>) {
-    eval.builtins.extend(import::import_builtins(io));
-
+pub fn add_import_builtins<'co, 'ro, 'env, IO>(
+    eval_builder: tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO>,
+    io: Rc<TvixStoreIO>,
+) -> tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO> {
     // TODO(raitobezarius): evaluate expressing filterSource as Nix code using path (b/372)
+    eval_builder.add_builtins(import::import_builtins(io))
 }
 
 #[cfg(test)]
@@ -81,11 +86,11 @@ mod tests {
             runtime.handle().clone(),
         ));
 
-        let mut eval = tvix_eval::Evaluation::new(io.clone() as Rc<dyn EvalIO>, false);
-
-        add_derivation_builtins(&mut eval, Rc::clone(&io));
-        add_fetcher_builtins(&mut eval, Rc::clone(&io));
-        add_import_builtins(&mut eval, io);
+        let mut eval_builder = tvix_eval::Evaluation::builder(io.clone() as Rc<dyn EvalIO>);
+        eval_builder = add_derivation_builtins(eval_builder, Rc::clone(&io));
+        eval_builder = add_fetcher_builtins(eval_builder, Rc::clone(&io));
+        eval_builder = add_import_builtins(eval_builder, io);
+        let eval = eval_builder.build();
 
         // run the evaluation itself.
         eval.evaluate(str, None)

tvix/glue/src/lib.rs

@@ -14,12 +14,14 @@ mod tests;
 /// Tell the Evaluator to resolve `<nix>` to the path `/__corepkgs__`,
 /// which has special handling in [tvix_io::TvixIO].
 /// This is used in nixpkgs to import `fetchurl.nix` from `<nix>`.
-pub fn configure_nix_path<IO>(
-    eval: &mut tvix_eval::Evaluation<IO>,
+pub fn configure_nix_path<'co, 'ro, 'env, IO>(
+    eval_builder: tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO>,
     nix_search_path: &Option<String>,
-) {
-    eval.nix_path = nix_search_path
-        .as_ref()
-        .map(|p| format!("nix=/__corepkgs__:{}", p))
-        .or_else(|| Some("nix=/__corepkgs__".to_string()));
+) -> tvix_eval::EvaluationBuilder<'co, 'ro, 'env, IO> {
+    eval_builder.nix_path(
+        nix_search_path
+            .as_ref()
+            .map(|p| format!("nix=/__corepkgs__:{}", p))
+            .or_else(|| Some("nix=/__corepkgs__".to_string())),
+    )
 }

tvix/glue/src/tests/mod.rs

@@ -47,16 +47,18 @@ fn eval_test(code_path: PathBuf, expect_success: bool) {
         tokio_runtime.handle().clone(),
     ));
     // Wrap with TvixIO, so <nix/fetchurl.nix can be imported.
-    let mut eval = tvix_eval::Evaluation::new(
-        Box::new(TvixIO::new(tvix_store_io.clone() as Rc<dyn EvalIO>)) as Box<dyn EvalIO>,
-        true,
-    );
+    let mut eval_builder = tvix_eval::Evaluation::builder(Box::new(TvixIO::new(
+        tvix_store_io.clone() as Rc<dyn EvalIO>,
+    )) as Box<dyn EvalIO>)
+    .enable_import()
+    .strict();
 
-    eval.strict = true;
-    add_derivation_builtins(&mut eval, tvix_store_io.clone());
-    add_fetcher_builtins(&mut eval, tvix_store_io.clone());
-    add_import_builtins(&mut eval, tvix_store_io.clone());
-    configure_nix_path(&mut eval, &None);
+    eval_builder = add_derivation_builtins(eval_builder, Rc::clone(&tvix_store_io));
+    eval_builder = add_fetcher_builtins(eval_builder, Rc::clone(&tvix_store_io));
+    eval_builder = add_import_builtins(eval_builder, tvix_store_io);
+    eval_builder = configure_nix_path(eval_builder, &None);
+
+    let eval = eval_builder.build();
 
     let result = eval.evaluate(code, Some(code_path.clone()));
     let failed = match result.value {

tvix/glue/src/tvix_store_io.rs

@@ -653,11 +653,13 @@ mod tests {
             Arc::<DummyBuildService>::default(),
             tokio_runtime.handle().clone(),
         ));
-        let mut eval = tvix_eval::Evaluation::new(io.clone() as Rc<dyn EvalIO>, true);
 
-        add_derivation_builtins(&mut eval, io.clone());
-        add_fetcher_builtins(&mut eval, io.clone());
-        add_import_builtins(&mut eval, io);
+        let mut eval_builder =
+            tvix_eval::Evaluation::builder(io.clone() as Rc<dyn EvalIO>).enable_import();
+        eval_builder = add_derivation_builtins(eval_builder, Rc::clone(&io));
+        eval_builder = add_fetcher_builtins(eval_builder, Rc::clone(&io));
+        eval_builder = add_import_builtins(eval_builder, io);
+        let eval = eval_builder.build();
 
         // run the evaluation itself.
         eval.evaluate(str, None)