refactor(tvix/castore/import): make module, split off fs and error

Move error types and filesystem-specific functions to a separate file,
and keep the fs:: namespace in public exports.

Change-Id: I5e9e83ad78d9aea38553fafc293d3e4f8c31a8c1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11486
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Autosubmit: flokli <flokli@flokli.de>

tvix/castore/src/import/error.rs

@@ -0,0 +1,39 @@
+use std::{fs::FileType, path::PathBuf};
+
+use crate::Error as CastoreError;
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("failed to upload directory at {0}: {1}")]
+    UploadDirectoryError(PathBuf, CastoreError),
+
+    #[error("invalid encoding encountered for entry {0:?}")]
+    InvalidEncoding(PathBuf),
+
+    #[error("unable to stat {0}: {1}")]
+    UnableToStat(PathBuf, std::io::Error),
+
+    #[error("unable to open {0}: {1}")]
+    UnableToOpen(PathBuf, std::io::Error),
+
+    #[error("unable to read {0}: {1}")]
+    UnableToRead(PathBuf, std::io::Error),
+
+    #[error("unsupported file {0} type: {1:?}")]
+    UnsupportedFileType(PathBuf, FileType),
+}
+
+impl From<CastoreError> for Error {
+    fn from(value: CastoreError) -> Self {
+        match value {
+            CastoreError::InvalidRequest(_) => panic!("tvix bug"),
+            CastoreError::StorageError(_) => panic!("error"),
+        }
+    }
+}
+
+impl From<Error> for std::io::Error {
+    fn from(value: Error) -> Self {
+        std::io::Error::new(std::io::ErrorKind::Other, value)
+    }
+}