copies-rust: use the `entry` API for copy information too
The code end up being complicated, but it split out the case were we add a new
entry from the case were we overwrite one. And that is the goal here, being able
to easily track value overwrite.
Differential Revision: https://phab.mercurial-scm.org/D9495
use crate::utils::hg_path::HgPath;
use crate::utils::hg_path::HgPathBuf;
use crate::Revision;
use crate::NULL_REVISION;
use im_rc::ordmap::DiffItem;
use im_rc::ordmap::Entry;
use im_rc::ordmap::OrdMap;
use std::cmp::Ordering;
use std::collections::HashMap;
use std::convert::TryInto;
pub type PathCopies = HashMap<HgPathBuf, HgPathBuf>;
type PathToken = usize;
#[derive(Clone, Debug, PartialEq, Copy)]
struct TimeStampedPathCopy {
/// revision at which the copy information was added
rev: Revision,
/// the copy source, (Set to None in case of deletion of the associated
/// key)
path: Option<PathToken>,
}
/// maps CopyDestination to Copy Source (+ a "timestamp" for the operation)
type TimeStampedPathCopies = OrdMap<PathToken, TimeStampedPathCopy>;
/// hold parent 1, parent 2 and relevant files actions.
pub type RevInfo<'a> = (Revision, Revision, ChangedFiles<'a>);
/// represent the files affected by a changesets
///
/// This hold a subset of mercurial.metadata.ChangingFiles as we do not need
/// all the data categories tracked by it.
/// This hold a subset of mercurial.metadata.ChangingFiles as we do not need
/// all the data categories tracked by it.
pub struct ChangedFiles<'a> {
nb_items: u32,
index: &'a [u8],
data: &'a [u8],
}
/// Represent active changes that affect the copy tracing.
enum Action<'a> {
/// The parent ? children edge is removing a file
///
/// (actually, this could be the edge from the other parent, but it does
/// not matters)
Removed(&'a HgPath),
/// The parent ? children edge introduce copy information between (dest,
/// source)
Copied(&'a HgPath, &'a HgPath),
}
/// This express the possible "special" case we can get in a merge
///
/// See mercurial/metadata.py for details on these values.
#[derive(PartialEq)]
enum MergeCase {
/// Merged: file had history on both side that needed to be merged
Merged,
/// Salvaged: file was candidate for deletion, but survived the merge
Salvaged,
/// Normal: Not one of the two cases above
Normal,
}
type FileChange<'a> = (u8, &'a HgPath, &'a HgPath);
const EMPTY: &[u8] = b"";
const COPY_MASK: u8 = 3;
const P1_COPY: u8 = 2;
const P2_COPY: u8 = 3;
const ACTION_MASK: u8 = 28;
const REMOVED: u8 = 12;
const MERGED: u8 = 8;
const SALVAGED: u8 = 16;
impl<'a> ChangedFiles<'a> {
const INDEX_START: usize = 4;
const ENTRY_SIZE: u32 = 9;
const FILENAME_START: u32 = 1;
const COPY_SOURCE_START: u32 = 5;
pub fn new(data: &'a [u8]) -> Self {
assert!(
data.len() >= 4,
"data size ({}) is too small to contain the header (4)",
data.len()
);
let nb_items_raw: [u8; 4] = (&data[0..=3])
.try_into()
.expect("failed to turn 4 bytes into 4 bytes");
let nb_items = u32::from_be_bytes(nb_items_raw);
let index_size = (nb_items * Self::ENTRY_SIZE) as usize;
let index_end = Self::INDEX_START + index_size;
assert!(
data.len() >= index_end,
"data size ({}) is too small to fit the index_data ({})",
data.len(),
index_end
);
let ret = ChangedFiles {
nb_items,
index: &data[Self::INDEX_START..index_end],
data: &data[index_end..],
};
let max_data = ret.filename_end(nb_items - 1) as usize;
assert!(
ret.data.len() >= max_data,
"data size ({}) is too small to fit all data ({})",
data.len(),
index_end + max_data
);
ret
}
pub fn new_empty() -> Self {
ChangedFiles {
nb_items: 0,
index: EMPTY,
data: EMPTY,
}
}
/// internal function to return an individual entry at a given index
fn entry(&'a self, idx: u32) -> FileChange<'a> {
if idx >= self.nb_items {
panic!(
"index for entry is higher that the number of file {} >= {}",
idx, self.nb_items
)
}
let flags = self.flags(idx);
let filename = self.filename(idx);
let copy_idx = self.copy_idx(idx);
let copy_source = self.filename(copy_idx);
(flags, filename, copy_source)
}
/// internal function to return the filename of the entry at a given index
fn filename(&self, idx: u32) -> &HgPath {
let filename_start;
if idx == 0 {
filename_start = 0;
} else {
filename_start = self.filename_end(idx - 1)
}
let filename_end = self.filename_end(idx);
let filename_start = filename_start as usize;
let filename_end = filename_end as usize;
HgPath::new(&self.data[filename_start..filename_end])
}
/// internal function to return the flag field of the entry at a given
/// index
fn flags(&self, idx: u32) -> u8 {
let idx = idx as usize;
self.index[idx * (Self::ENTRY_SIZE as usize)]
}
/// internal function to return the end of a filename part at a given index
fn filename_end(&self, idx: u32) -> u32 {
let start = (idx * Self::ENTRY_SIZE) + Self::FILENAME_START;
let end = (idx * Self::ENTRY_SIZE) + Self::COPY_SOURCE_START;
let start = start as usize;
let end = end as usize;
let raw = (&self.index[start..end])
.try_into()
.expect("failed to turn 4 bytes into 4 bytes");
u32::from_be_bytes(raw)
}
/// internal function to return index of the copy source of the entry at a
/// given index
fn copy_idx(&self, idx: u32) -> u32 {
let start = (idx * Self::ENTRY_SIZE) + Self::COPY_SOURCE_START;
let end = (idx + 1) * Self::ENTRY_SIZE;
let start = start as usize;
let end = end as usize;
let raw = (&self.index[start..end])
.try_into()
.expect("failed to turn 4 bytes into 4 bytes");
u32::from_be_bytes(raw)
}
/// Return an iterator over all the `Action` in this instance.
fn iter_actions(&self, parent: Parent) -> ActionsIterator {
ActionsIterator {
changes: &self,
parent: parent,
current: 0,
}
}
/// return the MergeCase value associated with a filename
fn get_merge_case(&self, path: &HgPath) -> MergeCase {
if self.nb_items == 0 {
return MergeCase::Normal;
}
let mut low_part = 0;
let mut high_part = self.nb_items;
while low_part < high_part {
let cursor = (low_part + high_part - 1) / 2;
let (flags, filename, _source) = self.entry(cursor);
match path.cmp(filename) {
Ordering::Less => low_part = cursor + 1,
Ordering::Greater => high_part = cursor,
Ordering::Equal => {
return match flags & ACTION_MASK {
MERGED => MergeCase::Merged,
SALVAGED => MergeCase::Salvaged,
_ => MergeCase::Normal,
};
}
}
}
MergeCase::Normal
}
}
/// A struct responsible for answering "is X ancestors of Y" quickly
///
/// The structure will delegate ancestors call to a callback, and cache the
/// result.
#[derive(Debug)]
struct AncestorOracle<'a, A: Fn(Revision, Revision) -> bool> {
inner: &'a A,
pairs: HashMap<(Revision, Revision), bool>,
}
impl<'a, A: Fn(Revision, Revision) -> bool> AncestorOracle<'a, A> {
fn new(func: &'a A) -> Self {
Self {
inner: func,
pairs: HashMap::default(),
}
}
/// returns `true` if `anc` is an ancestors of `desc`, `false` otherwise
fn is_ancestor(&mut self, anc: Revision, desc: Revision) -> bool {
if anc > desc {
false
} else if anc == desc {
true
} else {
if let Some(b) = self.pairs.get(&(anc, desc)) {
*b
} else {
let b = (self.inner)(anc, desc);
self.pairs.insert((anc, desc), b);
b
}
}
}
}
struct ActionsIterator<'a> {
changes: &'a ChangedFiles<'a>,
parent: Parent,
current: u32,
}
impl<'a> Iterator for ActionsIterator<'a> {
type Item = Action<'a>;
fn next(&mut self) -> Option<Action<'a>> {
let copy_flag = match self.parent {
Parent::FirstParent => P1_COPY,
Parent::SecondParent => P2_COPY,
};
while self.current < self.changes.nb_items {
let (flags, file, source) = self.changes.entry(self.current);
self.current += 1;
if (flags & ACTION_MASK) == REMOVED {
return Some(Action::Removed(file));
}
let copy = flags & COPY_MASK;
if copy == copy_flag {
return Some(Action::Copied(file, source));
}
}
return None;
}
}
/// A small struct whose purpose is to ensure lifetime of bytes referenced in
/// ChangedFiles
///
/// It is passed to the RevInfoMaker callback who can assign any necessary
/// content to the `data` attribute. The copy tracing code is responsible for
/// keeping the DataHolder alive at least as long as the ChangedFiles object.
pub struct DataHolder<D> {
/// RevInfoMaker callback should assign data referenced by the
/// ChangedFiles struct it return to this attribute. The DataHolder
/// lifetime will be at least as long as the ChangedFiles one.
pub data: Option<D>,
}
pub type RevInfoMaker<'a, D> =
Box<dyn for<'r> Fn(Revision, &'r mut DataHolder<D>) -> RevInfo<'r> + 'a>;
/// enum used to carry information about the parent → child currently processed
#[derive(Copy, Clone, Debug)]
enum Parent {
/// The `p1(x) → x` edge
FirstParent,
/// The `p2(x) → x` edge
SecondParent,
}
/// A small "tokenizer" responsible of turning full HgPath into lighter
/// PathToken
///
/// Dealing with small object, like integer is much faster, so HgPath input are
/// turned into integer "PathToken" and converted back in the end.
#[derive(Clone, Debug, Default)]
struct TwoWayPathMap {
token: HashMap<HgPathBuf, PathToken>,
path: Vec<HgPathBuf>,
}
impl TwoWayPathMap {
fn tokenize(&mut self, path: &HgPath) -> PathToken {
match self.token.get(path) {
Some(a) => *a,
None => {
let a = self.token.len();
let buf = path.to_owned();
self.path.push(buf.clone());
self.token.insert(buf, a);
a
}
}
}
fn untokenize(&self, token: PathToken) -> &HgPathBuf {
assert!(token < self.path.len(), format!("Unknown token: {}", token));
&self.path[token]
}
}
/// Same as mercurial.copies._combine_changeset_copies, but in Rust.
///
/// Arguments are:
///
/// revs: all revisions to be considered
/// children: a {parent ? [childrens]} mapping
/// target_rev: the final revision we are combining copies to
/// rev_info(rev): callback to get revision information:
/// * first parent
/// * second parent
/// * ChangedFiles
/// isancestors(low_rev, high_rev): callback to check if a revision is an
/// ancestor of another
pub fn combine_changeset_copies<A: Fn(Revision, Revision) -> bool, D>(
revs: Vec<Revision>,
mut children_count: HashMap<Revision, usize>,
target_rev: Revision,
rev_info: RevInfoMaker<D>,
is_ancestor: &A,
) -> PathCopies {
let mut all_copies = HashMap::new();
let mut oracle = AncestorOracle::new(is_ancestor);
let mut path_map = TwoWayPathMap::default();
for rev in revs {
let mut d: DataHolder<D> = DataHolder { data: None };
let (p1, p2, changes) = rev_info(rev, &mut d);
// We will chain the copies information accumulated for the parent with
// the individual copies information the curent revision. Creating a
// new TimeStampedPath for each `rev` → `children` vertex.
let mut copies: Option<TimeStampedPathCopies> = None;
if p1 != NULL_REVISION {
// Retrieve data computed in a previous iteration
let parent_copies = get_and_clean_parent_copies(
&mut all_copies,
&mut children_count,
p1,
);
if let Some(parent_copies) = parent_copies {
// combine it with data for that revision
let vertex_copies = add_from_changes(
&mut path_map,
&parent_copies,
&changes,
Parent::FirstParent,
rev,
);
// keep that data around for potential later combination
copies = Some(vertex_copies);
}
}
if p2 != NULL_REVISION {
// Retrieve data computed in a previous iteration
let parent_copies = get_and_clean_parent_copies(
&mut all_copies,
&mut children_count,
p2,
);
if let Some(parent_copies) = parent_copies {
// combine it with data for that revision
let vertex_copies = add_from_changes(
&mut path_map,
&parent_copies,
&changes,
Parent::SecondParent,
rev,
);
copies = match copies {
None => Some(vertex_copies),
// Merge has two parents needs to combines their copy
// information.
//
// If we got data from both parents, We need to combine
// them.
Some(copies) => Some(merge_copies_dict(
&path_map,
vertex_copies,
copies,
&changes,
&mut oracle,
)),
};
}
}
match copies {
Some(copies) => {
all_copies.insert(rev, copies);
}
_ => {}
}
}
// Drop internal information (like the timestamp) and return the final
// mapping.
let tt_result = all_copies
.remove(&target_rev)
.expect("target revision was not processed");
let mut result = PathCopies::default();
for (dest, tt_source) in tt_result {
if let Some(path) = tt_source.path {
let path_dest = path_map.untokenize(dest).to_owned();
let path_path = path_map.untokenize(path).to_owned();
result.insert(path_dest, path_path);
}
}
result
}
/// fetch previous computed information
///
/// If no other children are expected to need this information, we drop it from
/// the cache.
///
/// If parent is not part of the set we are expected to walk, return None.
fn get_and_clean_parent_copies(
all_copies: &mut HashMap<Revision, TimeStampedPathCopies>,
children_count: &mut HashMap<Revision, usize>,
parent_rev: Revision,
) -> Option<TimeStampedPathCopies> {
let count = children_count.get_mut(&parent_rev)?;
*count -= 1;
if *count == 0 {
match all_copies.remove(&parent_rev) {
Some(c) => Some(c),
None => Some(TimeStampedPathCopies::default()),
}
} else {
match all_copies.get(&parent_rev) {
Some(c) => Some(c.clone()),
None => Some(TimeStampedPathCopies::default()),
}
}
}
/// Combine ChangedFiles with some existing PathCopies information and return
/// the result
fn add_from_changes(
path_map: &mut TwoWayPathMap,
base_copies: &TimeStampedPathCopies,
changes: &ChangedFiles,
parent: Parent,
current_rev: Revision,
) -> TimeStampedPathCopies {
let mut copies = base_copies.clone();
for action in changes.iter_actions(parent) {
match action {
Action::Copied(path_dest, path_source) => {
let dest = path_map.tokenize(path_dest);
let source = path_map.tokenize(path_source);
let entry;
if let Some(v) = base_copies.get(&source) {
entry = match &v.path {
Some(path) => Some((*(path)).to_owned()),
None => Some(source.to_owned()),
}
} else {
entry = Some(source.to_owned());
}
// Each new entry is introduced by the children, we
// record this information as we will need it to take
// the right decision when merging conflicting copy
// information. See merge_copies_dict for details.
match copies.entry(dest) {
Entry::Vacant(slot) => {
let ttpc = TimeStampedPathCopy {
rev: current_rev,
path: entry,
};
slot.insert(ttpc);
}
Entry::Occupied(mut slot) => {
let mut ttpc = slot.get_mut();
ttpc.rev = current_rev;
ttpc.path = entry;
}
}
}
Action::Removed(deleted_path) => {
// We must drop copy information for removed file.
//
// We need to explicitly record them as dropped to
// propagate this information when merging two
// TimeStampedPathCopies object.
let deleted = path_map.tokenize(deleted_path);
copies.entry(deleted).and_modify(|old| {
old.rev = current_rev;
old.path = None;
});
}
}
}
copies
}
/// merge two copies-mapping together, minor and major
///
/// In case of conflict, value from "major" will be picked, unless in some
/// cases. See inline documentation for details.
fn merge_copies_dict<A: Fn(Revision, Revision) -> bool>(
path_map: &TwoWayPathMap,
mut minor: TimeStampedPathCopies,
mut major: TimeStampedPathCopies,
changes: &ChangedFiles,
oracle: &mut AncestorOracle<A>,
) -> TimeStampedPathCopies {
// This closure exist as temporary help while multiple developper are
// actively working on this code. Feel free to re-inline it once this
// code is more settled.
let mut cmp_value =
|dest: &PathToken,
src_minor: &TimeStampedPathCopy,
src_major: &TimeStampedPathCopy| {
compare_value(
path_map, changes, oracle, dest, src_minor, src_major,
)
};
if minor.is_empty() {
major
} else if major.is_empty() {
minor
} else if minor.len() * 2 < major.len() {
// Lets says we are merging two TimeStampedPathCopies instance A and B.
//
// If A contains N items, the merge result will never contains more
// than N values differents than the one in A
//
// If B contains M items, with M > N, the merge result will always
// result in a minimum of M - N value differents than the on in
// A
//
// As a result, if N < (M-N), we know that simply iterating over A will
// yield less difference than iterating over the difference
// between A and B.
//
// This help performance a lot in case were a tiny
// TimeStampedPathCopies is merged with a much larger one.
for (dest, src_minor) in minor {
let src_major = major.get(&dest);
match src_major {
None => major.insert(dest, src_minor),
Some(src_major) => {
match cmp_value(&dest, &src_minor, src_major) {
MergePick::Any | MergePick::Major => None,
MergePick::Minor => major.insert(dest, src_minor),
}
}
};
}
major
} else if major.len() * 2 < minor.len() {
// This use the same rational than the previous block.
// (Check previous block documentation for details.)
for (dest, src_major) in major {
let src_minor = minor.get(&dest);
match src_minor {
None => minor.insert(dest, src_major),
Some(src_minor) => {
match cmp_value(&dest, src_minor, &src_major) {
MergePick::Any | MergePick::Minor => None,
MergePick::Major => minor.insert(dest, src_major),
}
}
};
}
minor
} else {
let mut override_minor = Vec::new();
let mut override_major = Vec::new();
let mut to_major = |k: &PathToken, v: &TimeStampedPathCopy| {
override_major.push((k.clone(), v.clone()))
};
let mut to_minor = |k: &PathToken, v: &TimeStampedPathCopy| {
override_minor.push((k.clone(), v.clone()))
};
// The diff function leverage detection of the identical subpart if
// minor and major has some common ancestors. This make it very
// fast is most case.
//
// In case where the two map are vastly different in size, the current
// approach is still slowish because the iteration will iterate over
// all the "exclusive" content of the larger on. This situation can be
// frequent when the subgraph of revision we are processing has a lot
// of roots. Each roots adding they own fully new map to the mix (and
// likely a small map, if the path from the root to the "main path" is
// small.
//
// We could do better by detecting such situation and processing them
// differently.
for d in minor.diff(&major) {
match d {
DiffItem::Add(k, v) => to_minor(k, v),
DiffItem::Remove(k, v) => to_major(k, v),
DiffItem::Update { old, new } => {
let (dest, src_major) = new;
let (_, src_minor) = old;
match cmp_value(dest, src_minor, src_major) {
MergePick::Major => to_minor(dest, src_major),
MergePick::Minor => to_major(dest, src_minor),
// If the two entry are identical, no need to do
// anything (but diff should not have yield them)
MergePick::Any => unreachable!(),
}
}
};
}
let updates;
let mut result;
if override_major.is_empty() {
result = major
} else if override_minor.is_empty() {
result = minor
} else {
if override_minor.len() < override_major.len() {
updates = override_minor;
result = minor;
} else {
updates = override_major;
result = major;
}
for (k, v) in updates {
result.insert(k, v);
}
}
result
}
}
/// represent the side that should prevail when merging two
/// TimeStampedPathCopies
enum MergePick {
/// The "major" (p1) side prevails
Major,
/// The "minor" (p2) side prevails
Minor,
/// Any side could be used (because they are the same)
Any,
}
/// decide which side prevails in case of conflicting values
#[allow(clippy::if_same_then_else)]
fn compare_value<A: Fn(Revision, Revision) -> bool>(
path_map: &TwoWayPathMap,
changes: &ChangedFiles,
oracle: &mut AncestorOracle<A>,
dest: &PathToken,
src_minor: &TimeStampedPathCopy,
src_major: &TimeStampedPathCopy,
) -> MergePick {
if src_major.path == src_minor.path {
// we have the same value, but from other source;
if src_major.rev == src_minor.rev {
// If the two entry are identical, they are both valid
MergePick::Any
} else if oracle.is_ancestor(src_major.rev, src_minor.rev) {
MergePick::Minor
} else {
MergePick::Major
}
} else if src_major.rev == src_minor.rev {
// We cannot get copy information for both p1 and p2 in the
// same rev. So this is the same value.
unreachable!(
"conflict information from p1 and p2 in the same revision"
);
} else {
let dest_path = path_map.untokenize(*dest);
let action = changes.get_merge_case(dest_path);
if src_major.path.is_none() && action == MergeCase::Salvaged {
// If the file is "deleted" in the major side but was
// salvaged by the merge, we keep the minor side alive
MergePick::Minor
} else if src_minor.path.is_none() && action == MergeCase::Salvaged {
// If the file is "deleted" in the minor side but was
// salvaged by the merge, unconditionnaly preserve the
// major side.
MergePick::Major
} else if action == MergeCase::Merged {
// If the file was actively merged, copy information
// from each side might conflict. The major side will
// win such conflict.
MergePick::Major
} else if oracle.is_ancestor(src_major.rev, src_minor.rev) {
// If the minor side is strictly newer than the major
// side, it should be kept.
MergePick::Minor
} else if src_major.path.is_some() {
// without any special case, the "major" value win
// other the "minor" one.
MergePick::Major
} else if oracle.is_ancestor(src_minor.rev, src_major.rev) {
// the "major" rev is a direct ancestors of "minor",
// any different value should
// overwrite
MergePick::Major
} else {
// major version is None (so the file was deleted on
// that branch) and that branch is independant (neither
// minor nor major is an ancestors of the other one.)
// We preserve the new
// information about the new file.
MergePick::Minor
}
}
}