fix(tvix/nix-compat): clean up the debug assertions a bit r/6766

Consistent error messages, and slightly nicer code layout. We avoid
printing the input data, since we primarily want to point out the
specific violated invariant. In the one place where we do want to,
we use BStr's Debug implementation, since byte slices don't print
nicely.

Change-Id: I3a9a0c37be270ea5f16cf124922c254608fb849e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9617
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: edef <edef@edef.eu>

1 files changed, 11 insertions, 12 deletions

diff --git a/tvix/nix-compat/src/nar/writer/mod.rs b/tvix/nix-compat/src/nar/writer/mod.rs
index f73d323e3820..9abc2510d149 100644
--- a/tvix/nix-compat/src/nar/writer/mod.rs
+++ b/tvix/nix-compat/src/nar/writer/mod.rs
@@ -28,6 +28,7 @@
 //! # Ok::<(), std::io::Error>(())
 //! ```
 
+use bstr::ByteSlice;
 use std::io::{
     self, BufRead,
     ErrorKind::{InvalidInput, UnexpectedEof},
@@ -73,11 +74,8 @@ impl<'a, 'w> Node<'a, 'w> {
             "target.len() > {}",
             wire::MAX_TARGET_LEN
         );
-        debug_assert!(
-            !target.contains(&b'\0'),
-            "invalid target characters: {target:?}"
-        );
-        debug_assert!(!target.is_empty(), "empty target");
+        debug_assert!(!target.is_empty(), "target is empty");
+        debug_assert!(!target.contains(&0), "target contains null byte");
 
         self.write(&wire::TOK_SYM)?;
         self.write(&target.len().to_le_bytes())?;
@@ -176,12 +174,11 @@ impl<'a, 'w> Directory<'a, 'w> {
             "name.len() > {}",
             wire::MAX_NAME_LEN
         );
-        debug_assert!(name != b"", "name may not be empty");
-        debug_assert!(name != b".", "invalid name: {name:?}");
-        debug_assert!(name != b"..", "invalid name: {name:?}");
-
-        debug_assert!(!name.contains(&b'/'), "invalid name characters: {name:?}");
-        debug_assert!(!name.contains(&b'\0'), "invalid name characters: {name:?}");
+        debug_assert!(!name.is_empty(), "name is empty");
+        debug_assert!(!name.contains(&0), "name contains null byte");
+        debug_assert!(!name.contains(&b'/'), "name contains {:?}", '/');
+        debug_assert!(name != b".", "name == {:?}", ".");
+        debug_assert!(name != b"..", "name == {:?}", "..");
 
         match self.prev_name {
             None => {
@@ -192,7 +189,9 @@ impl<'a, 'w> Directory<'a, 'w> {
                 {
                     assert!(
                         &**_prev_name < name,
-                        "misordered names: {_prev_name:?} >= {name:?}"
+                        "misordered names: {:?} >= {:?}",
+                        _prev_name.as_bstr(),
+                        name.as_bstr()
                     );
                     _prev_name.clear();
                     _prev_name.extend_from_slice(name);