1 files changed, 68 insertions, 0 deletions
diff --git a/tvix/glue/src/tvix_io.rs b/tvix/glue/src/tvix_io.rs
new file mode 100644
index 000000000000..19e5dd0b41df
--- /dev/null
+++ b/tvix/glue/src/tvix_io.rs
@@ -0,0 +1,68 @@
+//! 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::io;
+use std::path::{Path, PathBuf};
+use tvix_eval::{EvalIO, FileType};
+
+// TODO: Merge this together with TvixStoreIO?
+pub struct TvixIO<T> {
+    // Actual underlying [EvalIO] implementation.
+    actual: T,
+}
+
+impl<T> TvixIO<T> {
+    pub fn new(actual: T) -> Self {
+        Self { actual }
+    }
+}
+
+impl<T> EvalIO for TvixIO<T>
+where
+    T: AsRef<dyn EvalIO>,
+{
+    fn store_dir(&self) -> Option<String> {
+        self.actual.as_ref().store_dir()
+    }
+
+    fn import_path(&self, path: &Path) -> io::Result<PathBuf> {
+        let imported_path = self.actual.as_ref().import_path(path)?;
+        Ok(imported_path)
+    }
+
+    fn path_exists(&self, path: &Path) -> io::Result<bool> {
+        if path.starts_with("/__corepkgs__") {
+            return Ok(true);
+        }
+
+        self.actual.as_ref().path_exists(path)
+    }
+
+    fn read_to_string(&self, path: &Path) -> io::Result<String> {
+        // Bundled version of corepkgs/fetchurl.nix. The counterpart
+        // of this happens in [crate::configure_nix_path], 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.as_ref().read_to_string(path)
+    }
+
+    fn read_dir(&self, path: &Path) -> io::Result<Vec<(bytes::Bytes, FileType)>> {
+        self.actual.as_ref().read_dir(path)
+    }
+}