hex_util: move common_hex_len() from backend module

This function predates the hex_util module. If there were hex_util, I would
add it there.

lib/src/backend.rs

@@ -424,26 +424,6 @@ impl Tree {
     }
 }
 
-/// Calculates common prefix length of two bytes. The length to be returned is
-/// a number of hexadecimal digits.
-pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {
-    iter_half_bytes(bytes_a)
-        .zip(iter_half_bytes(bytes_b))
-        .take_while(|(a, b)| a == b)
-        .count()
-}
-
-fn iter_half_bytes(bytes: &[u8]) -> impl ExactSizeIterator<Item = u8> + '_ {
-    (0..bytes.len() * 2).map(|i| {
-        let v = bytes[i / 2];
-        if i & 1 == 0 {
-            v >> 4
-        } else {
-            v & 0xf
-        }
-    })
-}
-
 pub fn make_root_commit(root_change_id: ChangeId, empty_tree_id: TreeId) -> Commit {
     let timestamp = Timestamp {
         timestamp: MillisSinceEpoch(0),

lib/src/default_index/composite.rs

@@ -30,7 +30,7 @@ use crate::backend::{ChangeId, CommitId, ObjectId};
 use crate::index::{HexPrefix, Index, PrefixResolution};
 use crate::revset::{ResolvedExpression, Revset, RevsetEvaluationError};
 use crate::store::Store;
-use crate::{backend, default_revset_engine};
+use crate::{default_revset_engine, hex_util};
 
 pub(super) trait IndexSegment: Send + Sync {
     fn num_parent_commits(&self) -> u32;
@@ -319,7 +319,7 @@ impl Index for CompositeIndex<'_> {
     fn shortest_unique_commit_id_prefix_len(&self, commit_id: &CommitId) -> usize {
         let (prev_id, next_id) = self.resolve_neighbor_commit_ids(commit_id);
         itertools::chain(prev_id, next_id)
-            .map(|id| backend::common_hex_len(commit_id.as_bytes(), id.as_bytes()) + 1)
+            .map(|id| hex_util::common_hex_len(commit_id.as_bytes(), id.as_bytes()) + 1)
             .max()
             .unwrap_or(0)
     }

lib/src/hex_util.rs

@@ -51,6 +51,26 @@ pub fn to_reverse_hex(forward_hex: &str) -> Option<String> {
         .collect()
 }
 
+/// Calculates common prefix length of two bytes. The length to be returned is
+/// a number of hexadecimal digits.
+pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {
+    iter_half_bytes(bytes_a)
+        .zip(iter_half_bytes(bytes_b))
+        .take_while(|(a, b)| a == b)
+        .count()
+}
+
+fn iter_half_bytes(bytes: &[u8]) -> impl ExactSizeIterator<Item = u8> + '_ {
+    (0..bytes.len() * 2).map(|i| {
+        let v = bytes[i / 2];
+        if i & 1 == 0 {
+            v >> 4
+        } else {
+            v & 0xf
+        }
+    })
+}
+
 #[cfg(test)]
 #[cfg(test)]
 mod tests {

lib/src/id_prefix.rs

@@ -21,7 +21,8 @@ use std::rc::Rc;
 use itertools::Itertools as _;
 use once_cell::unsync::OnceCell;
 
-use crate::backend::{self, ChangeId, CommitId, ObjectId};
+use crate::backend::{ChangeId, CommitId, ObjectId};
+use crate::hex_util;
 use crate::index::{HexPrefix, PrefixResolution};
 use crate::repo::Repo;
 use crate::revset::{DefaultSymbolResolver, RevsetExpression};
@@ -421,7 +422,7 @@ where
 
         // Left/right neighbors should have unique short keys. For the current chunk,
         // we need to look up full-length keys.
-        let unique_len = |a: &[u8], b: &[u8]| backend::common_hex_len(a, b) + 1;
+        let unique_len = |a: &[u8], b: &[u8]| hex_util::common_hex_len(a, b) + 1;
         let neighbor_lens = left
             .iter()
             .chain(&right)