feat(nix-compat/{aterm,derivation}): init parser r/6831

This provides a nom-based parser for Nix derivations in ATerm format,
which can be reached via `Derivation::from_aterm_bytes`.

Some of the lower-level ATerm primitives are moved into a (new) aterm
module, and some more higher-level ones that construct derivation-
specific types.

Also, move the escape_bytes function into there, this is a generic ATerm
thing.

Change-Id: I2b03b8a1461c7ea2fcb8640c2fc3d1fa3ea719fb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9730
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

1 files changed, 27 insertions, 0 deletions

diff --git a/tvix/nix-compat/src/aterm/escape.rs b/tvix/nix-compat/src/aterm/escape.rs
new file mode 100644
index 000000000000..06b550bbf02d
--- /dev/null
+++ b/tvix/nix-compat/src/aterm/escape.rs
@@ -0,0 +1,27 @@
+use bstr::ByteSlice;
+
+/// Escapes a byte sequence. Does not add surrounding quotes.
+pub fn escape_bytes<P: AsRef<[u8]>>(s: P) -> Vec<u8> {
+    let mut s: Vec<u8> = s.as_ref().to_vec();
+
+    s = s.replace(b"\\", b"\\\\");
+    s = s.replace(b"\n", b"\\n");
+    s = s.replace(b"\r", b"\\r");
+    s = s.replace(b"\t", b"\\t");
+    s = s.replace(b"\"", b"\\\"");
+
+    s
+}
+
+#[cfg(test)]
+mod tests {
+    use super::escape_bytes;
+    use test_case::test_case;
+
+    #[test_case(b"", b""; "empty")]
+    #[test_case(b"\"", b"\\\""; "doublequote")]
+    #[test_case(b":", b":"; "colon")]
+    fn escape(input: &[u8], expected: &[u8]) {
+        assert_eq!(expected, escape_bytes(input))
+    }
+}