feat(tvix/eval): introduce ErrorKind::InvalidHash

The nixhash errors were wrapped in a generic TvixError. Now it has its
own TvixError with unique error code. The nixhash error is passed along
as a string.

The errors looked like:

error[E997]: invalid encoded digest length '51' for algo sha256

Now they look like:

error[E041]: Invalid hash: invalid encoded digest length '51' for algo
sha256

Change-Id: I5c420815538ba4c6567c95f5d44d60c4d48f43fd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12718
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/eval/src/errors.rs

@@ -236,6 +236,9 @@ to a missing value in the attribute set(s) included via `with`."#
     #[error("Invalid UTF-8 in string")]
     Utf8,
 
+    #[error("Invalid hash: {0}")]
+    InvalidHash(String),
+
     /// Variant for errors that bubble up to eval from other Tvix
     /// components.
     #[error("{0}")]
@@ -676,6 +679,7 @@ impl Error {
             | ErrorKind::NotImplemented(_)
             | ErrorKind::WithContext { .. }
             | ErrorKind::UnknownHashType(_)
+            | ErrorKind::InvalidHash(_)
             | ErrorKind::CatchableError(_) => return None,
         };
 
@@ -722,6 +726,7 @@ impl Error {
             ErrorKind::Utf8 => "E038",
             ErrorKind::UnknownHashType(_) => "E039",
             ErrorKind::UnexpectedArgumentBuiltin { .. } => "E040",
+            ErrorKind::InvalidHash(_) => "E041",
 
             // Special error code for errors from other Tvix
             // components. We may want to introduce a code namespacing

tvix/glue/src/builtins/fetchers.rs

@@ -73,8 +73,7 @@ async fn extract_fetch_args(
     let sha256 = match sha256_str {
         Some(sha256_str) => {
             let nixhash = nixhash::from_str(&sha256_str, Some("sha256"))
-                // TODO: DerivationError::InvalidOutputHash should be moved to ErrorKind::InvalidHash and used here instead
+                .map_err(|e| ErrorKind::InvalidHash(e.to_string()))?;
-                .map_err(|e| ErrorKind::TvixError(Rc::new(e)))?;
 
             Some(nixhash.digest_as_bytes().try_into().expect("is sha256"))
         }