refactor(tvix): move tvix glue code into glue crate r/6936

There's various bits and pieces in tvix-cli that use both the store and
evaluator, as well as nix-compat. For example, builtins.derivation, as
well as the reference scanning implementation.

This "glue code" currently isn't accessible from anywhere else, but it'd
be very useful if it were.

Move it out into a `glue` crate, and make `tvix-cli` a consumer of it.

All the KnownPaths setup and passing around, as well as NIX_PATH
handling is also something that should probably be moved into the glue
crate as well, but that's something left for a future CL.

Change-Id: I080ed3d1825ab23790666486840f301f00856277
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9908
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

1 files changed, 80 insertions, 0 deletions

diff --git a/tvix/glue/src/tvix_io.rs b/tvix/glue/src/tvix_io.rs
new file mode 100644
index 0000000000..caadbeb5e6
--- /dev/null
+++ b/tvix/glue/src/tvix_io.rs
@@ -0,0 +1,80 @@
+//! This module implements a wrapper around tvix-eval's [EvalIO] type,
+//! adding functionality which is required by tvix-cli:
+//!
+//! 1. Marking plain paths known to the reference scanner.
+//! 2. Handling the C++ Nix `__corepkgs__`-hack for nixpkgs bootstrapping.
+//!
+//! All uses of [EvalIO] in tvix-cli must make use of this wrapper,
+//! otherwise fundamental features like nixpkgs bootstrapping and hash
+//! calculation will not work.
+
+use std::cell::RefCell;
+use std::io;
+use std::path::{Path, PathBuf};
+use std::rc::Rc;
+use tvix_eval::{EvalIO, FileType};
+
+use crate::known_paths::KnownPaths;
+
+// TODO: Merge this together with TvixStoreIO?
+pub struct TvixIO<T: EvalIO> {
+    /// Ingested paths must be reported to this known paths tracker
+    /// for accurate build reference scanning.
+    known_paths: Rc<RefCell<KnownPaths>>,
+
+    // Actual underlying [EvalIO] implementation.
+    actual: T,
+}
+
+impl<T: EvalIO> TvixIO<T> {
+    pub fn new(known_paths: Rc<RefCell<KnownPaths>>, actual: T) -> Self {
+        Self {
+            known_paths,
+            actual,
+        }
+    }
+}
+
+impl<T: EvalIO> EvalIO for TvixIO<T> {
+    fn store_dir(&self) -> Option<String> {
+        self.actual.store_dir()
+    }
+
+    fn import_path(&self, path: &Path) -> Result<PathBuf, io::Error> {
+        let imported_path = self.actual.import_path(path)?;
+        self.known_paths
+            .borrow_mut()
+            .plain(imported_path.to_string_lossy());
+
+        Ok(imported_path)
+    }
+
+    fn path_exists(&self, path: &Path) -> Result<bool, io::Error> {
+        if path.starts_with("/__corepkgs__") {
+            return Ok(true);
+        }
+
+        self.actual.path_exists(path)
+    }
+
+    fn read_to_string(&self, path: &Path) -> Result<String, io::Error> {
+        // Bundled version of corepkgs/fetchurl.nix. The counterpart
+        // of this happens in `main`, where the `nix_path` of the
+        // evaluation has `nix=/__corepkgs__` added to it.
+        //
+        // This workaround is similar to what cppnix does for passing
+        // the path through.
+        //
+        // TODO: this comparison is bad and allocates, we should use
+        // the sane path library.
+        if path.starts_with("/__corepkgs__/fetchurl.nix") {
+            return Ok(include_str!("fetchurl.nix").to_string());
+        }
+
+        self.actual.read_to_string(path)
+    }
+
+    fn read_dir(&self, path: &Path) -> Result<Vec<(bytes::Bytes, FileType)>, io::Error> {
+        self.actual.read_dir(path)
+    }
+}