rust-parsers: use in-place mutation instead of allocating a new `Vec`

This is not done for the `dirstate-tree` feature, since it lacks `iter_mut`.

Differential Revision: https://phab.mercurial-scm.org/D9136

rust/hg-core/src/dirstate/parsers.rs

@@ -1,518 +1,512
 // Copyright 2019 Raphaël Gomès <[e-mail]>
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 
 use crate::utils::hg_path::HgPath;
 use crate::{
     dirstate::{CopyMap, EntryState, StateMap},
     DirstateEntry, DirstatePackError, DirstateParents, DirstateParseError,
 };
 use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
 use micro_timer::timed;
 use std::convert::{TryFrom, TryInto};
 use std::io::Cursor;
 use std::time::Duration;
 
 /// Parents are stored in the dirstate as byte hashes.
 pub const PARENT_SIZE: usize = 20;
 /// Dirstate entries have a static part of 8 + 32 + 32 + 32 + 32 bits.
 const MIN_ENTRY_SIZE: usize = 17;
 
 type ParseResult<'a> = (
     DirstateParents,
     Vec<(&'a HgPath, DirstateEntry)>,
     Vec<(&'a HgPath, &'a HgPath)>,
 );
 
 #[timed]
 pub fn parse_dirstate(
     contents: &[u8],
 ) -> Result<ParseResult, DirstateParseError> {
     if contents.len() < PARENT_SIZE * 2 {
         return Err(DirstateParseError::TooLittleData);
     }
     let mut copies = vec![];
     let mut entries = vec![];
 
     let mut curr_pos = PARENT_SIZE * 2;
     let parents = DirstateParents {
         p1: contents[..PARENT_SIZE].try_into().unwrap(),
         p2: contents[PARENT_SIZE..curr_pos].try_into().unwrap(),
     };
 
     while curr_pos < contents.len() {
         if curr_pos + MIN_ENTRY_SIZE > contents.len() {
             return Err(DirstateParseError::Overflow);
         }
         let entry_bytes = &contents[curr_pos..];
 
         let mut cursor = Cursor::new(entry_bytes);
         let state = EntryState::try_from(cursor.read_u8()?)?;
         let mode = cursor.read_i32::<BigEndian>()?;
         let size = cursor.read_i32::<BigEndian>()?;
         let mtime = cursor.read_i32::<BigEndian>()?;
         let path_len = cursor.read_i32::<BigEndian>()? as usize;
 
         if path_len > contents.len() - curr_pos {
             return Err(DirstateParseError::Overflow);
         }
 
         // Slice instead of allocating a Vec needed for `read_exact`
         let path = &entry_bytes[MIN_ENTRY_SIZE..MIN_ENTRY_SIZE + (path_len)];
 
         let (path, copy) = match memchr::memchr(0, path) {
             None => (path, None),
             Some(i) => (&path[..i], Some(&path[(i + 1)..])),
         };
 
         if let Some(copy_path) = copy {
             copies.push((HgPath::new(path), HgPath::new(copy_path)));
         };
         entries.push((
             HgPath::new(path),
             DirstateEntry {
                 state,
                 mode,
                 size,
                 mtime,
             },
         ));
         curr_pos = curr_pos + MIN_ENTRY_SIZE + (path_len);
     }
     Ok((parents, entries, copies))
 }
 
 /// `now` is the duration in seconds since the Unix epoch
 #[cfg(not(feature = "dirstate-tree"))]
 pub fn pack_dirstate(
     state_map: &mut StateMap,
     copy_map: &CopyMap,
     parents: DirstateParents,
     now: Duration,
 ) -> Result<Vec<u8>, DirstatePackError> {
     // TODO move away from i32 before 2038.
     let now: i32 = now.as_secs().try_into().expect("time overflow");
 
     let expected_size: usize = state_map
         .iter()
         .map(|(filename, _)| {
             let mut length = MIN_ENTRY_SIZE + filename.len();
             if let Some(copy) = copy_map.get(filename) {
                 length += copy.len() + 1;
             }
             length
         })
         .sum();
     let expected_size = expected_size + PARENT_SIZE * 2;
 
     let mut packed = Vec::with_capacity(expected_size);
-    let mut new_state_map = vec![];
 
     packed.extend(&parents.p1);
     packed.extend(&parents.p2);
 
-    for (filename, entry) in state_map.iter() {
+    for (filename, entry) in state_map.iter_mut() {
         let new_filename = filename.to_owned();
         let mut new_mtime: i32 = entry.mtime;
         if entry.state == EntryState::Normal && entry.mtime == now {
             // The file was last modified "simultaneously" with the current
             // write to dirstate (i.e. within the same second for file-
             // systems with a granularity of 1 sec). This commonly happens
             // for at least a couple of files on 'update'.
             // The user could change the file without changing its size
             // within the same second. Invalidate the file's mtime in
             // dirstate, forcing future 'status' calls to compare the
             // contents of the file if the size is the same. This prevents
             // mistakenly treating such files as clean.
             new_mtime = -1;
-            new_state_map.push((
-                filename.to_owned(),
-                DirstateEntry {
-                    mtime: new_mtime,
-                    ..*entry
-                },
-            ));
+            *entry = DirstateEntry {
+                mtime: new_mtime,
+                ..*entry
+            };
         }
         let mut new_filename = new_filename.into_vec();
         if let Some(copy) = copy_map.get(filename) {
             new_filename.push(b'\0');
             new_filename.extend(copy.bytes());
         }
 
         packed.write_u8(entry.state.into())?;
         packed.write_i32::<BigEndian>(entry.mode)?;
         packed.write_i32::<BigEndian>(entry.size)?;
         packed.write_i32::<BigEndian>(new_mtime)?;
         packed.write_i32::<BigEndian>(new_filename.len() as i32)?;
         packed.extend(new_filename)
     }
 
     if packed.len() != expected_size {
         return Err(DirstatePackError::BadSize(expected_size, packed.len()));
     }
 
-    state_map.extend(new_state_map);
-
     Ok(packed)
 }
 /// `now` is the duration in seconds since the Unix epoch
 #[cfg(feature = "dirstate-tree")]
 pub fn pack_dirstate(
     state_map: &mut StateMap,
     copy_map: &CopyMap,
     parents: DirstateParents,
     now: Duration,
 ) -> Result<Vec<u8>, DirstatePackError> {
     // TODO move away from i32 before 2038.
     let now: i32 = now.as_secs().try_into().expect("time overflow");
 
     let expected_size: usize = state_map
         .iter()
         .map(|(filename, _)| {
             let mut length = MIN_ENTRY_SIZE + filename.len();
             if let Some(copy) = copy_map.get(&filename) {
                 length += copy.len() + 1;
             }
             length
         })
         .sum();
     let expected_size = expected_size + PARENT_SIZE * 2;
 
     let mut packed = Vec::with_capacity(expected_size);
     let mut new_state_map = vec![];
 
     packed.extend(&parents.p1);
     packed.extend(&parents.p2);
 
     for (filename, entry) in state_map.iter() {
         let new_filename = filename.to_owned();
         let mut new_mtime: i32 = entry.mtime;
         if entry.state == EntryState::Normal && entry.mtime == now {
             // The file was last modified "simultaneously" with the current
             // write to dirstate (i.e. within the same second for file-
             // systems with a granularity of 1 sec). This commonly happens
             // for at least a couple of files on 'update'.
             // The user could change the file without changing its size
             // within the same second. Invalidate the file's mtime in
             // dirstate, forcing future 'status' calls to compare the
             // contents of the file if the size is the same. This prevents
             // mistakenly treating such files as clean.
             new_mtime = -1;
             new_state_map.push((
                 filename.to_owned(),
                 DirstateEntry {
                     mtime: new_mtime,
                     ..entry
                 },
             ));
         }
         let mut new_filename = new_filename.into_vec();
         if let Some(copy) = copy_map.get(&filename) {
             new_filename.push(b'\0');
             new_filename.extend(copy.bytes());
         }
 
         packed.write_u8(entry.state.into())?;
         packed.write_i32::<BigEndian>(entry.mode)?;
         packed.write_i32::<BigEndian>(entry.size)?;
         packed.write_i32::<BigEndian>(new_mtime)?;
         packed.write_i32::<BigEndian>(new_filename.len() as i32)?;
         packed.extend(new_filename)
     }
 
     if packed.len() != expected_size {
         return Err(DirstatePackError::BadSize(expected_size, packed.len()));
     }
 
     state_map.extend(new_state_map);
 
     Ok(packed)
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::{utils::hg_path::HgPathBuf, FastHashMap};
     use pretty_assertions::assert_eq;
 
     #[test]
     fn test_pack_dirstate_empty() {
         let mut state_map = StateMap::default();
         let copymap = FastHashMap::default();
         let parents = DirstateParents {
             p1: *b"12345678910111213141",
             p2: *b"00000000000000000000",
         };
         let now = Duration::new(15000000, 0);
         let expected = b"1234567891011121314100000000000000000000".to_vec();
 
         assert_eq!(
             expected,
             pack_dirstate(&mut state_map, &copymap, parents, now).unwrap()
         );
 
         assert!(state_map.is_empty())
     }
     #[test]
     fn test_pack_dirstate_one_entry() {
         let expected_state_map: StateMap = [(
             HgPathBuf::from_bytes(b"f1"),
             DirstateEntry {
                 state: EntryState::Normal,
                 mode: 0o644,
                 size: 0,
                 mtime: 791231220,
             },
         )]
         .iter()
         .cloned()
         .collect();
         let mut state_map = expected_state_map.clone();
 
         let copymap = FastHashMap::default();
         let parents = DirstateParents {
             p1: *b"12345678910111213141",
             p2: *b"00000000000000000000",
         };
         let now = Duration::new(15000000, 0);
         let expected = [
             49, 50, 51, 52, 53, 54, 55, 56, 57, 49, 48, 49, 49, 49, 50, 49,
             51, 49, 52, 49, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
             48, 48, 48, 48, 48, 48, 48, 48, 110, 0, 0, 1, 164, 0, 0, 0, 0, 47,
             41, 58, 244, 0, 0, 0, 2, 102, 49,
         ]
         .to_vec();
 
         assert_eq!(
             expected,
             pack_dirstate(&mut state_map, &copymap, parents, now).unwrap()
         );
 
         assert_eq!(expected_state_map, state_map);
     }
     #[test]
     fn test_pack_dirstate_one_entry_with_copy() {
         let expected_state_map: StateMap = [(
             HgPathBuf::from_bytes(b"f1"),
             DirstateEntry {
                 state: EntryState::Normal,
                 mode: 0o644,
                 size: 0,
                 mtime: 791231220,
             },
         )]
         .iter()
         .cloned()
         .collect();
         let mut state_map = expected_state_map.clone();
         let mut copymap = FastHashMap::default();
         copymap.insert(
             HgPathBuf::from_bytes(b"f1"),
             HgPathBuf::from_bytes(b"copyname"),
         );
         let parents = DirstateParents {
             p1: *b"12345678910111213141",
             p2: *b"00000000000000000000",
         };
         let now = Duration::new(15000000, 0);
         let expected = [
             49, 50, 51, 52, 53, 54, 55, 56, 57, 49, 48, 49, 49, 49, 50, 49,
             51, 49, 52, 49, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
             48, 48, 48, 48, 48, 48, 48, 48, 110, 0, 0, 1, 164, 0, 0, 0, 0, 47,
             41, 58, 244, 0, 0, 0, 11, 102, 49, 0, 99, 111, 112, 121, 110, 97,
             109, 101,
         ]
         .to_vec();
 
         assert_eq!(
             expected,
             pack_dirstate(&mut state_map, &copymap, parents, now).unwrap()
         );
         assert_eq!(expected_state_map, state_map);
     }
 
     #[test]
     fn test_parse_pack_one_entry_with_copy() {
         let mut state_map: StateMap = [(
             HgPathBuf::from_bytes(b"f1"),
             DirstateEntry {
                 state: EntryState::Normal,
                 mode: 0o644,
                 size: 0,
                 mtime: 791231220,
             },
         )]
         .iter()
         .cloned()
         .collect();
         let mut copymap = FastHashMap::default();
         copymap.insert(
             HgPathBuf::from_bytes(b"f1"),
             HgPathBuf::from_bytes(b"copyname"),
         );
         let parents = DirstateParents {
             p1: *b"12345678910111213141",
             p2: *b"00000000000000000000",
         };
         let now = Duration::new(15000000, 0);
         let result =
             pack_dirstate(&mut state_map, &copymap, parents.clone(), now)
                 .unwrap();
 
         let (new_parents, entries, copies) =
             parse_dirstate(result.as_slice()).unwrap();
         let new_state_map: StateMap = entries
             .into_iter()
             .map(|(path, entry)| (path.to_owned(), entry))
             .collect();
         let new_copy_map: CopyMap = copies
             .into_iter()
             .map(|(path, copy)| (path.to_owned(), copy.to_owned()))
             .collect();
 
         assert_eq!(
             (parents, state_map, copymap),
             (new_parents, new_state_map, new_copy_map)
         )
     }
 
     #[test]
     fn test_parse_pack_multiple_entries_with_copy() {
         let mut state_map: StateMap = [
             (
                 HgPathBuf::from_bytes(b"f1"),
                 DirstateEntry {
                     state: EntryState::Normal,
                     mode: 0o644,
                     size: 0,
                     mtime: 791231220,
                 },
             ),
             (
                 HgPathBuf::from_bytes(b"f2"),
                 DirstateEntry {
                     state: EntryState::Merged,
                     mode: 0o777,
                     size: 1000,
                     mtime: 791231220,
                 },
             ),
             (
                 HgPathBuf::from_bytes(b"f3"),
                 DirstateEntry {
                     state: EntryState::Removed,
                     mode: 0o644,
                     size: 234553,
                     mtime: 791231220,
                 },
             ),
             (
                 HgPathBuf::from_bytes(b"f4\xF6"),
                 DirstateEntry {
                     state: EntryState::Added,
                     mode: 0o644,
                     size: -1,
                     mtime: -1,
                 },
             ),
         ]
         .iter()
         .cloned()
         .collect();
         let mut copymap = FastHashMap::default();
         copymap.insert(
             HgPathBuf::from_bytes(b"f1"),
             HgPathBuf::from_bytes(b"copyname"),
         );
         copymap.insert(
             HgPathBuf::from_bytes(b"f4\xF6"),
             HgPathBuf::from_bytes(b"copyname2"),
         );
         let parents = DirstateParents {
             p1: *b"12345678910111213141",
             p2: *b"00000000000000000000",
         };
         let now = Duration::new(15000000, 0);
         let result =
             pack_dirstate(&mut state_map, &copymap, parents.clone(), now)
                 .unwrap();
 
         let (new_parents, entries, copies) =
             parse_dirstate(result.as_slice()).unwrap();
         let new_state_map: StateMap = entries
             .into_iter()
             .map(|(path, entry)| (path.to_owned(), entry))
             .collect();
         let new_copy_map: CopyMap = copies
             .into_iter()
             .map(|(path, copy)| (path.to_owned(), copy.to_owned()))
             .collect();
 
         assert_eq!(
             (parents, state_map, copymap),
             (new_parents, new_state_map, new_copy_map)
         )
     }
 
     #[test]
     /// https://www.mercurial-scm.org/repo/hg/rev/af3f26b6bba4
     fn test_parse_pack_one_entry_with_copy_and_time_conflict() {
         let mut state_map: StateMap = [(
             HgPathBuf::from_bytes(b"f1"),
             DirstateEntry {
                 state: EntryState::Normal,
                 mode: 0o644,
                 size: 0,
                 mtime: 15000000,
             },
         )]
         .iter()
         .cloned()
         .collect();
         let mut copymap = FastHashMap::default();
         copymap.insert(
             HgPathBuf::from_bytes(b"f1"),
             HgPathBuf::from_bytes(b"copyname"),
         );
         let parents = DirstateParents {
             p1: *b"12345678910111213141",
             p2: *b"00000000000000000000",
         };
         let now = Duration::new(15000000, 0);
         let result =
             pack_dirstate(&mut state_map, &copymap, parents.clone(), now)
                 .unwrap();
 
         let (new_parents, entries, copies) =
             parse_dirstate(result.as_slice()).unwrap();
         let new_state_map: StateMap = entries
             .into_iter()
             .map(|(path, entry)| (path.to_owned(), entry))
             .collect();
         let new_copy_map: CopyMap = copies
             .into_iter()
             .map(|(path, copy)| (path.to_owned(), copy.to_owned()))
             .collect();
 
         assert_eq!(
             (
                 parents,
                 [(
                     HgPathBuf::from_bytes(b"f1"),
                     DirstateEntry {
                         state: EntryState::Normal,
                         mode: 0o644,
                         size: 0,
                         mtime: -1
                     }
                 )]
                 .iter()
                 .cloned()
                 .collect::<StateMap>(),
                 copymap,
             ),
             (new_parents, new_state_map, new_copy_map)
         )
     }
 }