rust-index: drop offset_override

The inline `offsets` value diverge from the one on disk for added value, so the
offset_override tricks is not going to work well once we start having the full
revlog logic in Rust.

We remove it beforehand and align the Rust logic to the Python one (adjusting
the segment offset at read time for inline revlog).

rust/hg-core/src/revlog/index.rs

@@ -18,11 +18,12 b' use crate::{'
 };
 
 pub const INDEX_ENTRY_SIZE: usize = 64;
+pub const INDEX_HEADER_SIZE: usize = 4;
 pub const COMPRESSION_MODE_INLINE: u8 = 2;
 
 #[derive(Debug)]
 pub struct IndexHeader {
-    pub(super) header_bytes: [u8; 4],
+    pub(super) header_bytes: [u8; INDEX_HEADER_SIZE],
 }
 
 #[derive(Copy, Clone)]
@@ -92,14 +93,21 b' struct IndexData {'
     truncation: Option<usize>,
     /// Bytes that were added after reading the index
     added: Vec<u8>,
+    first_entry: [u8; INDEX_ENTRY_SIZE],
 }
 
 impl IndexData {
     pub fn new(bytes: Box<dyn Deref<Target = [u8]> + Send + Sync>) -> Self {
+        let mut first_entry = [0; INDEX_ENTRY_SIZE];
+        if bytes.len() >= INDEX_ENTRY_SIZE {
+            first_entry[INDEX_HEADER_SIZE..]
+                .copy_from_slice(&bytes[INDEX_HEADER_SIZE..INDEX_ENTRY_SIZE])
+        }
         Self {
             bytes,
             truncation: None,
             added: vec![],
+            first_entry,
         }
     }
 
@@ -356,7 +364,6 b' impl Index {'
                 let end = offset + INDEX_ENTRY_SIZE;
                 let entry = IndexEntry {
                     bytes: &bytes[offset..end],
-                    offset_override: None,
                 };
 
                 offset += INDEX_ENTRY_SIZE + entry.compressed_len() as usize;
@@ -449,11 +456,17 b' impl Index {'
         if rev == NULL_REVISION {
             return None;
         }
-        Some(if self.is_inline() {
-            self.get_entry_inline(rev)
+        if rev.0 == 0 {
+            Some(IndexEntry {
+                bytes: &self.bytes.first_entry[..],
+            })
         } else {
-            self.get_entry_separated(rev)
-        })
+            Some(if self.is_inline() {
+                self.get_entry_inline(rev)
+            } else {
+                self.get_entry_separated(rev)
+            })
+        }
     }
 
     /// Return the binary content of the index entry for the given revision
@@ -512,13 +525,7 b' impl Index {'
         let end = start + INDEX_ENTRY_SIZE;
         let bytes = &self.bytes[start..end];
 
-        // See IndexEntry for an explanation of this override.
-        let offset_override = Some(end);
-
-        IndexEntry {
-            bytes,
-            offset_override,
-        }
+        IndexEntry { bytes }
     }
 
     fn get_entry_separated(&self, rev: Revision) -> IndexEntry {
@@ -526,20 +533,12 b' impl Index {'
         let end = start + INDEX_ENTRY_SIZE;
         let bytes = &self.bytes[start..end];
 
-        // Override the offset of the first revision as its bytes are used
-        // for the index's metadata (saving space because it is always 0)
-        let offset_override = if rev == Revision(0) { Some(0) } else { None };
-
-        IndexEntry {
-            bytes,
-            offset_override,
-        }
+        IndexEntry { bytes }
     }
 
     fn null_entry(&self) -> IndexEntry {
         IndexEntry {
             bytes: &[0; INDEX_ENTRY_SIZE],
-            offset_override: Some(0),
         }
     }
 
@@ -755,13 +754,20 b' impl Index {'
         revision_data: RevisionDataParams,
     ) -> Result<(), RevlogError> {
         revision_data.validate()?;
+        let entry_v1 = revision_data.into_v1();
+        let entry_bytes = entry_v1.as_bytes();
+        if self.bytes.len() == 0 {
+            self.bytes.first_entry[INDEX_HEADER_SIZE..].copy_from_slice(
+                &entry_bytes[INDEX_HEADER_SIZE..INDEX_ENTRY_SIZE],
+            )
+        }
         if self.is_inline() {
             let new_offset = self.bytes.len();
             if let Some(offsets) = &mut *self.get_offsets_mut() {
                 offsets.push(new_offset)
             }
         }
-        self.bytes.added.extend(revision_data.into_v1().as_bytes());
+        self.bytes.added.extend(entry_bytes);
         self.clear_head_revs();
         Ok(())
     }
@@ -1654,7 +1660,6 b' fn inline_scan(bytes: &[u8]) -> (usize, '
         let end = offset + INDEX_ENTRY_SIZE;
         let entry = IndexEntry {
             bytes: &bytes[offset..end],
-            offset_override: None,
         };
 
         offset += INDEX_ENTRY_SIZE + entry.compressed_len() as usize;
@@ -1678,29 +1683,14 b' impl super::RevlogIndex for Index {'
 #[derive(Debug)]
 pub struct IndexEntry<'a> {
     bytes: &'a [u8],
-    /// Allows to override the offset value of the entry.
-    ///
-    /// For interleaved index and data, the offset stored in the index
-    /// corresponds to the separated data offset.
-    /// It has to be overridden with the actual offset in the interleaved
-    /// index which is just after the index block.
-    ///
-    /// For separated index and data, the offset stored in the first index
-    /// entry is mixed with the index headers.
-    /// It has to be overridden with 0.
-    offset_override: Option<usize>,
 }
 
 impl<'a> IndexEntry<'a> {
     /// Return the offset of the data.
     pub fn offset(&self) -> usize {
-        if let Some(offset_override) = self.offset_override {
-            offset_override
-        } else {
-            let mut bytes = [0; 8];
-            bytes[2..8].copy_from_slice(&self.bytes[0..=5]);
-            BigEndian::read_u64(&bytes[..]) as usize
-        }
+        let mut bytes = [0; 8];
+        bytes[2..8].copy_from_slice(&self.bytes[0..=5]);
+        BigEndian::read_u64(&bytes[..]) as usize
     }
     pub fn raw_offset(&self) -> u64 {
         BigEndian::read_u64(&self.bytes[0..8])
@@ -1956,32 +1946,15 b' mod tests {'
     #[test]
     fn test_offset() {
         let bytes = IndexEntryBuilder::new().with_offset(1).build();
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.offset(), 1)
     }
 
     #[test]
-    fn test_with_overridden_offset() {
-        let bytes = IndexEntryBuilder::new().with_offset(1).build();
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: Some(2),
-        };
-
-        assert_eq!(entry.offset(), 2)
-    }
-
-    #[test]
     fn test_compressed_len() {
         let bytes = IndexEntryBuilder::new().with_compressed_len(1).build();
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.compressed_len(), 1)
     }
@@ -1989,10 +1962,7 b' mod tests {'
     #[test]
     fn test_uncompressed_len() {
         let bytes = IndexEntryBuilder::new().with_uncompressed_len(1).build();
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.uncompressed_len(), 1)
     }
@@ -2002,10 +1972,7 b' mod tests {'
         let bytes = IndexEntryBuilder::new()
             .with_base_revision_or_base_of_delta_chain(Revision(1))
             .build();
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.base_revision_or_base_of_delta_chain(), 1.into())
     }
@@ -2016,10 +1983,7 b' mod tests {'
             .with_link_revision(Revision(123))
             .build();
 
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.link_revision(), 123.into());
     }
@@ -2028,10 +1992,7 b' mod tests {'
     fn p1_test() {
         let bytes = IndexEntryBuilder::new().with_p1(Revision(123)).build();
 
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.p1(), 123.into());
     }
@@ -2040,10 +2001,7 b' mod tests {'
     fn p2_test() {
         let bytes = IndexEntryBuilder::new().with_p2(Revision(123)).build();
 
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(entry.p2(), 123.into());
     }
@@ -2054,10 +2012,7 b' mod tests {'
             .unwrap();
         let bytes = IndexEntryBuilder::new().with_node(node).build();
 
-        let entry = IndexEntry {
-            bytes: &bytes,
-            offset_override: None,
-        };
+        let entry = IndexEntry { bytes: &bytes };
 
         assert_eq!(*entry.hash(), node);
     }

rust/hg-core/src/revlog/mod.rs

@@ -29,6 +29,7 b' use zstd;'
 use self::node::{NODE_BYTES_LENGTH, NULL_NODE};
 use self::nodemap_docket::NodeMapDocket;
 use super::index::Index;
+use super::index::INDEX_ENTRY_SIZE;
 use super::nodemap::{NodeMap, NodeMapError};
 use crate::errors::HgError;
 use crate::vfs::Vfs;
@@ -531,7 +532,12 b' impl Revlog {'
             .index
             .get_entry(rev)
             .ok_or(RevlogError::InvalidRevision)?;
-        let start = index_entry.offset();
+        let offset = index_entry.offset();
+        let start = if self.index.is_inline() {
+            offset + ((rev.0 as usize + 1) * INDEX_ENTRY_SIZE)
+        } else {
+            offset
+        };
         let end = start + index_entry.compressed_len() as usize;
         let data = if self.index.is_inline() {
             self.index.data(start, end)