feat(tvix/glue): Implement builtins.storePath r/8217

This one's relatively simple - we just check if the store path exists,
and if it does we make a new contextful string containing the store path
as its only context element.

Automatic testing seems tricky for this (I think?) so I tested it
manually:

tvix-repl> builtins.storePath /nix/store/yn46i4xx5alh7gs6fpkxk430i34rp2q9-hello-2.12.1
=> "/nix/store/yn46i4xx5alh7gs6fpkxk430i34rp2q9-hello-2.12.1" :: string

Change-Id: I8a0d9726e4102ab872c53c2419679c2c855a5a18
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11696
Tested-by: BuildkiteCI
Autosubmit: aspen <root@gws.fyi>
Reviewed-by: flokli <flokli@flokli.de>

1 files changed, 5 insertions, 1 deletions

diff --git a/tvix/glue/src/builtins/errors.rs b/tvix/glue/src/builtins/errors.rs
index f6d5745c56e2..af8a24e6abb8 100644
--- a/tvix/glue/src/builtins/errors.rs
+++ b/tvix/glue/src/builtins/errors.rs
@@ -4,7 +4,7 @@ use nix_compat::{
     store_path::BuildStorePathError,
 };
 use reqwest::Url;
-use std::rc::Rc;
+use std::{path::PathBuf, rc::Rc};
 use thiserror::Error;
 use tvix_castore::import;
 
@@ -65,8 +65,12 @@ pub enum FetcherError {
 pub enum ImportError {
     #[error("non-file '{0}' cannot be imported in 'flat' mode")]
     FlatImportOfNonFile(String),
+
     #[error("hash mismatch at ingestion of '{0}', expected: '{1}', got: '{2}'")]
     HashMismatch(String, NixHash, NixHash),
+
+    #[error("path '{}' is not in the Nix store", .0.display())]
+    PathNotInStore(PathBuf),
 }
 
 impl From<ImportError> for tvix_eval::ErrorKind {