feat(tvix/glue): support builtin:fetchurl r/8254

nixpkgs calls <nix/fetchurl.nix> during nixpkgs bootstrap.

This produces a fake derivation with system = builtin
and builder = builtin:fetchurl, and needs to download files from the
internet.

At the end of the Derivation construction, if we have such a derivation,
also synthesize a `Fetch` struct, which we add to the known fetch paths.

This will then cause these fetches to be picked up like all other
fetches in TvixStoreIO.

Change-Id: I72cbca4f85da106b25eda97693a6a6e59911cd57
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10975
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

1 files changed, 12 insertions, 0 deletions

diff --git a/tvix/glue/src/builtins/derivation.rs b/tvix/glue/src/builtins/derivation.rs
index 7878ce0ed9ad..f266141cb6e7 100644
--- a/tvix/glue/src/builtins/derivation.rs
+++ b/tvix/glue/src/builtins/derivation.rs
@@ -170,6 +170,7 @@ pub(crate) mod derivation_builtins {
     use std::collections::BTreeMap;
 
     use crate::builtins::utils::{select_string, strong_importing_coerce_to_string};
+    use crate::fetchurl::fetchurl_derivation_to_fetch;
 
     use super::*;
     use bstr::ByteSlice;
@@ -506,6 +507,17 @@ pub(crate) mod derivation_builtins {
                 ))),
         )));
 
+        // If the derivation is a fake derivation (builtins:fetchurl),
+        // synthesize a [Fetch] and add it there, too.
+        if drv.builder == "builtin:fetchurl" {
+            let (name, fetch) =
+                fetchurl_derivation_to_fetch(&drv).map_err(|e| ErrorKind::TvixError(Rc::new(e)))?;
+
+            known_paths
+                .add_fetch(fetch, &name)
+                .map_err(|e| ErrorKind::TvixError(Rc::new(e)))?;
+        }
+
         // Register the Derivation in known_paths.
         known_paths.add_derivation(drv_path, drv);