fix(nix-compat/nixbase32): mark encode_len/decode_len const

Change-Id: Ib688bbb37cd54cfcd01e5cb3a8c376414ee8311e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9926
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

nix-compat/src/nixbase32.rs

@@ -134,12 +134,12 @@ fn find_invalid(input: &[u8]) -> u8 {
 }
 
 /// Returns the decoded length of an input of length len.
-pub fn decode_len(len: usize) -> usize {
+pub const fn decode_len(len: usize) -> usize {
     (len * 5) / 8
 }
 
 /// Returns the encoded length of an input of length len
-pub fn encode_len(len: usize) -> usize {
+pub const fn encode_len(len: usize) -> usize {
     (len * 8 + 4) / 5
 }
 

nix-compat/src/store_path/mod.rs

@@ -15,9 +15,7 @@ mod utils;
 pub use utils::*;
 
 pub const DIGEST_SIZE: usize = 20;
-// lazy_static doesn't allow us to call NIXBASE32.encode_len(), so we ran it
-// manually and have an assert in the tests.
-pub const ENCODED_DIGEST_SIZE: usize = 32;
+pub const ENCODED_DIGEST_SIZE: usize = nixbase32::encode_len(DIGEST_SIZE);
 
 // The store dir prefix, without trailing slash.
 // That's usually where the Nix store is mounted at.
@@ -298,11 +296,6 @@ mod tests {
 
     use super::{Error, StorePath};
 
-    #[test]
-    fn encoded_digest_size() {
-        assert_eq!(ENCODED_DIGEST_SIZE, nixbase32::encode_len(DIGEST_SIZE));
-    }
-
     #[test]
     fn happy_path() {
         let example_nix_path_str =