rust-dirstate: make the reliable timestamp comparison more usable from outside

This is going to be used with pre-computed times unlike in status.

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

@@ -1,722 +1,727
 use crate::dirstate_tree::on_disk::DirstateV2ParseError;
 use crate::errors::HgError;
 use bitflags::bitflags;
 use std::fs;
 use std::io;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum EntryState {
     Normal,
     Added,
     Removed,
     Merged,
 }
 
 /// `size` and `mtime.seconds` are truncated to 31 bits.
 ///
 /// TODO: double-check status algorithm correctness for files
 /// larger than 2 GiB or modified after 2038.
 #[derive(Debug, Copy, Clone)]
 pub struct DirstateEntry {
     pub(crate) flags: Flags,
     mode_size: Option<(u32, u32)>,
     mtime: Option<TruncatedTimestamp>,
 }
 
 bitflags! {
     pub(crate) struct Flags: u8 {
         const WDIR_TRACKED = 1 << 0;
         const P1_TRACKED = 1 << 1;
         const P2_INFO = 1 << 2;
         const HAS_FALLBACK_EXEC = 1 << 3;
         const FALLBACK_EXEC = 1 << 4;
         const HAS_FALLBACK_SYMLINK = 1 << 5;
         const FALLBACK_SYMLINK = 1 << 6;
     }
 }
 
 /// A Unix timestamp with nanoseconds precision
 #[derive(Debug, Copy, Clone)]
 pub struct TruncatedTimestamp {
     truncated_seconds: u32,
     /// Always in the `0 .. 1_000_000_000` range.
     nanoseconds: u32,
     /// TODO this should be in DirstateEntry, but the current code needs
     /// refactoring to use DirstateEntry instead of TruncatedTimestamp for
     /// comparison.
     pub second_ambiguous: bool,
 }
 
 impl TruncatedTimestamp {
     /// Constructs from a timestamp potentially outside of the supported range,
     /// and truncate the seconds components to its lower 31 bits.
     ///
     /// Panics if the nanoseconds components is not in the expected range.
     pub fn new_truncate(
         seconds: i64,
         nanoseconds: u32,
         second_ambiguous: bool,
     ) -> Self {
         assert!(nanoseconds < NSEC_PER_SEC);
         Self {
             truncated_seconds: seconds as u32 & RANGE_MASK_31BIT,
             nanoseconds,
             second_ambiguous,
         }
     }
 
     /// Construct from components. Returns an error if they are not in the
     /// expcted range.
     pub fn from_already_truncated(
         truncated_seconds: u32,
         nanoseconds: u32,
         second_ambiguous: bool,
     ) -> Result<Self, DirstateV2ParseError> {
         if truncated_seconds & !RANGE_MASK_31BIT == 0
             && nanoseconds < NSEC_PER_SEC
         {
             Ok(Self {
                 truncated_seconds,
                 nanoseconds,
                 second_ambiguous,
             })
         } else {
             Err(DirstateV2ParseError::new("when reading datetime"))
         }
     }
 
     /// Returns a `TruncatedTimestamp` for the modification time of `metadata`.
     ///
     /// Propagates errors from `std` on platforms where modification time
     /// is not available at all.
     pub fn for_mtime_of(metadata: &fs::Metadata) -> io::Result<Self> {
         #[cfg(unix)]
         {
             use std::os::unix::fs::MetadataExt;
             let seconds = metadata.mtime();
             // i64 -> u32 with value always in the `0 .. NSEC_PER_SEC` range
             let nanoseconds = metadata.mtime_nsec().try_into().unwrap();
             Ok(Self::new_truncate(seconds, nanoseconds, false))
         }
         #[cfg(not(unix))]
         {
             metadata.modified().map(Self::from)
         }
     }
 
     /// Like `for_mtime_of`, but may return `None` or a value with
     /// `second_ambiguous` set if the mtime is not "reliable".
     ///
     /// A modification time is reliable if it is older than `boundary` (or
     /// sufficiently in the future).
     ///
     /// Otherwise a concurrent modification might happens with the same mtime.
     pub fn for_reliable_mtime_of(
         metadata: &fs::Metadata,
         boundary: &Self,
     ) -> io::Result<Option<Self>> {
-        let mut mtime = Self::for_mtime_of(metadata)?;
+        Ok(Self::for_mtime_of(metadata)?.for_reliable_mtime_of_self(boundary))
+    }
+
+    /// See [`Self::for_reliable_mtime_of`]
+    pub fn for_reliable_mtime_of_self(&self, boundary: &Self) -> Option<Self> {
+        let mut new = *self;
         // If the mtime of the ambiguous file is younger (or equal) to the
         // starting point of the `status` walk, we cannot garantee that
         // another, racy, write will not happen right after with the same mtime
         // and we cannot cache the information.
         //
         // However if the mtime is far away in the future, this is likely some
         // mismatch between the current clock and previous file system
         // operation. So mtime more than one days in the future are considered
         // fine.
-        let reliable = if mtime.truncated_seconds == boundary.truncated_seconds
+        let reliable = if self.truncated_seconds == boundary.truncated_seconds
         {
-            mtime.second_ambiguous = true;
-            mtime.nanoseconds != 0
+            new.second_ambiguous = true;
+            self.nanoseconds != 0
                 && boundary.nanoseconds != 0
-                && mtime.nanoseconds < boundary.nanoseconds
+                && self.nanoseconds < boundary.nanoseconds
         } else {
             // `truncated_seconds` is less than 2**31,
             // so this does not overflow `u32`:
             let one_day_later = boundary.truncated_seconds + 24 * 3600;
-            mtime.truncated_seconds < boundary.truncated_seconds
-                || mtime.truncated_seconds > one_day_later
+            self.truncated_seconds < boundary.truncated_seconds
+                || self.truncated_seconds > one_day_later
         };
         if reliable {
-            Ok(Some(mtime))
+            Some(new)
         } else {
-            Ok(None)
+            None
         }
     }
 
     /// The lower 31 bits of the number of seconds since the epoch.
     pub fn truncated_seconds(&self) -> u32 {
         self.truncated_seconds
     }
 
     /// The sub-second component of this timestamp, in nanoseconds.
     /// Always in the `0 .. 1_000_000_000` range.
     ///
     /// This timestamp is after `(seconds, 0)` by this many nanoseconds.
     pub fn nanoseconds(&self) -> u32 {
         self.nanoseconds
     }
 
     /// Returns whether two timestamps are equal modulo 2**31 seconds.
     ///
     /// If this returns `true`, the original values converted from `SystemTime`
     /// or given to `new_truncate` were very likely equal. A false positive is
     /// possible if they were exactly a multiple of 2**31 seconds apart (around
     /// 68 years). This is deemed very unlikely to happen by chance, especially
     /// on filesystems that support sub-second precision.
     ///
     /// If someone is manipulating the modification times of some files to
     /// intentionally make `hg status` return incorrect results, not truncating
     /// wouldn’t help much since they can set exactly the expected timestamp.
     ///
     /// Sub-second precision is ignored if it is zero in either value.
     /// Some APIs simply return zero when more precision is not available.
     /// When comparing values from different sources, if only one is truncated
     /// in that way, doing a simple comparison would cause many false
     /// negatives.
     pub fn likely_equal(self, other: Self) -> bool {
         if self.truncated_seconds != other.truncated_seconds {
             false
         } else if self.nanoseconds == 0 || other.nanoseconds == 0 {
             !self.second_ambiguous
         } else {
             self.nanoseconds == other.nanoseconds
         }
     }
 
     pub fn likely_equal_to_mtime_of(
         self,
         metadata: &fs::Metadata,
     ) -> io::Result<bool> {
         Ok(self.likely_equal(Self::for_mtime_of(metadata)?))
     }
 }
 
 impl From<SystemTime> for TruncatedTimestamp {
     fn from(system_time: SystemTime) -> Self {
         // On Unix, `SystemTime` is a wrapper for the `timespec` C struct:
         // https://www.gnu.org/software/libc/manual/html_node/Time-Types.html#index-struct-timespec
         // We want to effectively access its fields, but the Rust standard
         // library does not expose them. The best we can do is:
         let seconds;
         let nanoseconds;
         match system_time.duration_since(UNIX_EPOCH) {
             Ok(duration) => {
                 seconds = duration.as_secs() as i64;
                 nanoseconds = duration.subsec_nanos();
             }
             Err(error) => {
                 // `system_time` is before `UNIX_EPOCH`.
                 // We need to undo this algorithm:
                 // https://github.com/rust-lang/rust/blob/6bed1f0bc3cc50c10aab26d5f94b16a00776b8a5/library/std/src/sys/unix/time.rs#L40-L41
                 let negative = error.duration();
                 let negative_secs = negative.as_secs() as i64;
                 let negative_nanos = negative.subsec_nanos();
                 if negative_nanos == 0 {
                     seconds = -negative_secs;
                     nanoseconds = 0;
                 } else {
                     // For example if `system_time` was 4.3 seconds before
                     // the Unix epoch we get a Duration that represents
                     // `(-4, -0.3)` but we want `(-5, +0.7)`:
                     seconds = -1 - negative_secs;
                     nanoseconds = NSEC_PER_SEC - negative_nanos;
                 }
             }
         };
         Self::new_truncate(seconds, nanoseconds, false)
     }
 }
 
 const NSEC_PER_SEC: u32 = 1_000_000_000;
 pub const RANGE_MASK_31BIT: u32 = 0x7FFF_FFFF;
 
 pub const MTIME_UNSET: i32 = -1;
 
 /// A `DirstateEntry` with a size of `-2` means that it was merged from the
 /// other parent. This allows revert to pick the right status back during a
 /// merge.
 pub const SIZE_FROM_OTHER_PARENT: i32 = -2;
 /// A special value used for internal representation of special case in
 /// dirstate v1 format.
 pub const SIZE_NON_NORMAL: i32 = -1;
 
 #[derive(Debug, Default, Copy, Clone)]
 pub struct DirstateV2Data {
     pub wc_tracked: bool,
     pub p1_tracked: bool,
     pub p2_info: bool,
     pub mode_size: Option<(u32, u32)>,
     pub mtime: Option<TruncatedTimestamp>,
     pub fallback_exec: Option<bool>,
     pub fallback_symlink: Option<bool>,
 }
 
 #[derive(Debug, Default, Copy, Clone)]
 pub struct ParentFileData {
     pub mode_size: Option<(u32, u32)>,
     pub mtime: Option<TruncatedTimestamp>,
 }
 
 impl DirstateEntry {
     pub fn from_v2_data(v2_data: DirstateV2Data) -> Self {
         let DirstateV2Data {
             wc_tracked,
             p1_tracked,
             p2_info,
             mode_size,
             mtime,
             fallback_exec,
             fallback_symlink,
         } = v2_data;
         if let Some((mode, size)) = mode_size {
             // TODO: return an error for out of range values?
             assert!(mode & !RANGE_MASK_31BIT == 0);
             assert!(size & !RANGE_MASK_31BIT == 0);
         }
         let mut flags = Flags::empty();
         flags.set(Flags::WDIR_TRACKED, wc_tracked);
         flags.set(Flags::P1_TRACKED, p1_tracked);
         flags.set(Flags::P2_INFO, p2_info);
         if let Some(exec) = fallback_exec {
             flags.insert(Flags::HAS_FALLBACK_EXEC);
             if exec {
                 flags.insert(Flags::FALLBACK_EXEC);
             }
         }
         if let Some(exec) = fallback_symlink {
             flags.insert(Flags::HAS_FALLBACK_SYMLINK);
             if exec {
                 flags.insert(Flags::FALLBACK_SYMLINK);
             }
         }
         Self {
             flags,
             mode_size,
             mtime,
         }
     }
 
     pub fn from_v1_data(
         state: EntryState,
         mode: i32,
         size: i32,
         mtime: i32,
     ) -> Self {
         match state {
             EntryState::Normal => {
                 if size == SIZE_FROM_OTHER_PARENT {
                     Self {
                         // might be missing P1_TRACKED
                         flags: Flags::WDIR_TRACKED | Flags::P2_INFO,
                         mode_size: None,
                         mtime: None,
                     }
                 } else if size == SIZE_NON_NORMAL {
                     Self {
                         flags: Flags::WDIR_TRACKED | Flags::P1_TRACKED,
                         mode_size: None,
                         mtime: None,
                     }
                 } else if mtime == MTIME_UNSET {
                     // TODO: return an error for negative values?
                     let mode = u32::try_from(mode).unwrap();
                     let size = u32::try_from(size).unwrap();
                     Self {
                         flags: Flags::WDIR_TRACKED | Flags::P1_TRACKED,
                         mode_size: Some((mode, size)),
                         mtime: None,
                     }
                 } else {
                     // TODO: return an error for negative values?
                     let mode = u32::try_from(mode).unwrap();
                     let size = u32::try_from(size).unwrap();
                     let mtime = u32::try_from(mtime).unwrap();
                     let mtime = TruncatedTimestamp::from_already_truncated(
                         mtime, 0, false,
                     )
                     .unwrap();
                     Self {
                         flags: Flags::WDIR_TRACKED | Flags::P1_TRACKED,
                         mode_size: Some((mode, size)),
                         mtime: Some(mtime),
                     }
                 }
             }
             EntryState::Added => Self {
                 flags: Flags::WDIR_TRACKED,
                 mode_size: None,
                 mtime: None,
             },
             EntryState::Removed => Self {
                 flags: if size == SIZE_NON_NORMAL {
                     Flags::P1_TRACKED | Flags::P2_INFO
                 } else if size == SIZE_FROM_OTHER_PARENT {
                     // We don’t know if P1_TRACKED should be set (file history)
                     Flags::P2_INFO
                 } else {
                     Flags::P1_TRACKED
                 },
                 mode_size: None,
                 mtime: None,
             },
             EntryState::Merged => Self {
                 flags: Flags::WDIR_TRACKED
                     | Flags::P1_TRACKED // might not be true because of rename ?
                     | Flags::P2_INFO, // might not be true because of rename ?
                 mode_size: None,
                 mtime: None,
             },
         }
     }
 
     /// Creates a new entry in "removed" state.
     ///
     /// `size` is expected to be zero, `SIZE_NON_NORMAL`, or
     /// `SIZE_FROM_OTHER_PARENT`
     pub fn new_removed(size: i32) -> Self {
         Self::from_v1_data(EntryState::Removed, 0, size, 0)
     }
 
     pub fn new_tracked() -> Self {
         let data = DirstateV2Data {
             wc_tracked: true,
             ..Default::default()
         };
         Self::from_v2_data(data)
     }
 
     pub fn tracked(&self) -> bool {
         self.flags.contains(Flags::WDIR_TRACKED)
     }
 
     pub fn p1_tracked(&self) -> bool {
         self.flags.contains(Flags::P1_TRACKED)
     }
 
     fn in_either_parent(&self) -> bool {
         self.flags.intersects(Flags::P1_TRACKED | Flags::P2_INFO)
     }
 
     pub fn removed(&self) -> bool {
         self.in_either_parent() && !self.flags.contains(Flags::WDIR_TRACKED)
     }
 
     pub fn p2_info(&self) -> bool {
         self.flags.contains(Flags::WDIR_TRACKED | Flags::P2_INFO)
     }
 
     pub fn added(&self) -> bool {
         self.flags.contains(Flags::WDIR_TRACKED) && !self.in_either_parent()
     }
 
     pub fn modified(&self) -> bool {
         self.flags
             .contains(Flags::WDIR_TRACKED | Flags::P1_TRACKED | Flags::P2_INFO)
     }
 
     pub fn maybe_clean(&self) -> bool {
         #[allow(clippy::if_same_then_else)]
         #[allow(clippy::needless_bool)]
         if !self.flags.contains(Flags::WDIR_TRACKED) {
             false
         } else if !self.flags.contains(Flags::P1_TRACKED) {
             false
         } else if self.flags.contains(Flags::P2_INFO) {
             false
         } else {
             true
         }
     }
 
     pub fn any_tracked(&self) -> bool {
         self.flags.intersects(
             Flags::WDIR_TRACKED | Flags::P1_TRACKED | Flags::P2_INFO,
         )
     }
 
     pub(crate) fn v2_data(&self) -> DirstateV2Data {
         if !self.any_tracked() {
             // TODO: return an Option instead?
             panic!("Accessing v2_data of an untracked DirstateEntry")
         }
         let wc_tracked = self.flags.contains(Flags::WDIR_TRACKED);
         let p1_tracked = self.flags.contains(Flags::P1_TRACKED);
         let p2_info = self.flags.contains(Flags::P2_INFO);
         let mode_size = self.mode_size;
         let mtime = self.mtime;
         DirstateV2Data {
             wc_tracked,
             p1_tracked,
             p2_info,
             mode_size,
             mtime,
             fallback_exec: self.get_fallback_exec(),
             fallback_symlink: self.get_fallback_symlink(),
         }
     }
 
     fn v1_state(&self) -> EntryState {
         if !self.any_tracked() {
             // TODO: return an Option instead?
             panic!("Accessing v1_state of an untracked DirstateEntry")
         }
         if self.removed() {
             EntryState::Removed
         } else if self.modified() {
             EntryState::Merged
         } else if self.added() {
             EntryState::Added
         } else {
             EntryState::Normal
         }
     }
 
     fn v1_mode(&self) -> i32 {
         if let Some((mode, _size)) = self.mode_size {
             i32::try_from(mode).unwrap()
         } else {
             0
         }
     }
 
     fn v1_size(&self) -> i32 {
         if !self.any_tracked() {
             // TODO: return an Option instead?
             panic!("Accessing v1_size of an untracked DirstateEntry")
         }
         if self.removed()
             && self.flags.contains(Flags::P1_TRACKED | Flags::P2_INFO)
         {
             SIZE_NON_NORMAL
         } else if self.flags.contains(Flags::P2_INFO) {
             SIZE_FROM_OTHER_PARENT
         } else if self.removed() {
             0
         } else if self.added() {
             SIZE_NON_NORMAL
         } else if let Some((_mode, size)) = self.mode_size {
             i32::try_from(size).unwrap()
         } else {
             SIZE_NON_NORMAL
         }
     }
 
     fn v1_mtime(&self) -> i32 {
         if !self.any_tracked() {
             // TODO: return an Option instead?
             panic!("Accessing v1_mtime of an untracked DirstateEntry")
         }
 
         #[allow(clippy::if_same_then_else)]
         if self.removed() {
             0
         } else if self.flags.contains(Flags::P2_INFO) {
             MTIME_UNSET
         } else if !self.flags.contains(Flags::P1_TRACKED) {
             MTIME_UNSET
         } else if let Some(mtime) = self.mtime {
             if mtime.second_ambiguous {
                 MTIME_UNSET
             } else {
                 i32::try_from(mtime.truncated_seconds()).unwrap()
             }
         } else {
             MTIME_UNSET
         }
     }
 
     // TODO: return `Option<EntryState>`? None when `!self.any_tracked`
     pub fn state(&self) -> EntryState {
         self.v1_state()
     }
 
     // TODO: return Option?
     pub fn mode(&self) -> i32 {
         self.v1_mode()
     }
 
     // TODO: return Option?
     pub fn size(&self) -> i32 {
         self.v1_size()
     }
 
     // TODO: return Option?
     pub fn mtime(&self) -> i32 {
         self.v1_mtime()
     }
 
     pub fn get_fallback_exec(&self) -> Option<bool> {
         if self.flags.contains(Flags::HAS_FALLBACK_EXEC) {
             Some(self.flags.contains(Flags::FALLBACK_EXEC))
         } else {
             None
         }
     }
 
     pub fn set_fallback_exec(&mut self, value: Option<bool>) {
         match value {
             None => {
                 self.flags.remove(Flags::HAS_FALLBACK_EXEC);
                 self.flags.remove(Flags::FALLBACK_EXEC);
             }
             Some(exec) => {
                 self.flags.insert(Flags::HAS_FALLBACK_EXEC);
                 if exec {
                     self.flags.insert(Flags::FALLBACK_EXEC);
                 }
             }
         }
     }
 
     pub fn get_fallback_symlink(&self) -> Option<bool> {
         if self.flags.contains(Flags::HAS_FALLBACK_SYMLINK) {
             Some(self.flags.contains(Flags::FALLBACK_SYMLINK))
         } else {
             None
         }
     }
 
     pub fn set_fallback_symlink(&mut self, value: Option<bool>) {
         match value {
             None => {
                 self.flags.remove(Flags::HAS_FALLBACK_SYMLINK);
                 self.flags.remove(Flags::FALLBACK_SYMLINK);
             }
             Some(symlink) => {
                 self.flags.insert(Flags::HAS_FALLBACK_SYMLINK);
                 if symlink {
                     self.flags.insert(Flags::FALLBACK_SYMLINK);
                 }
             }
         }
     }
 
     pub fn truncated_mtime(&self) -> Option<TruncatedTimestamp> {
         self.mtime
     }
 
     pub fn drop_merge_data(&mut self) {
         if self.flags.contains(Flags::P2_INFO) {
             self.flags.remove(Flags::P2_INFO);
             self.mode_size = None;
             self.mtime = None;
         }
     }
 
     pub fn set_possibly_dirty(&mut self) {
         self.mtime = None
     }
 
     pub fn set_clean(
         &mut self,
         mode: u32,
         size: u32,
         mtime: TruncatedTimestamp,
     ) {
         let size = size & RANGE_MASK_31BIT;
         self.flags.insert(Flags::WDIR_TRACKED | Flags::P1_TRACKED);
         self.mode_size = Some((mode, size));
         self.mtime = Some(mtime);
     }
 
     pub fn set_tracked(&mut self) {
         self.flags.insert(Flags::WDIR_TRACKED);
         // `set_tracked` is replacing various `normallookup` call. So we mark
         // the files as needing lookup
         //
         // Consider dropping this in the future in favor of something less
         // broad.
         self.mtime = None;
     }
 
     pub fn set_untracked(&mut self) {
         self.flags.remove(Flags::WDIR_TRACKED);
         self.mode_size = None;
         self.mtime = None;
     }
 
     /// Returns `(state, mode, size, mtime)` for the puprose of serialization
     /// in the dirstate-v1 format.
     ///
     /// This includes marker values such as `mtime == -1`. In the future we may
     /// want to not represent these cases that way in memory, but serialization
     /// will need to keep the same format.
     pub fn v1_data(&self) -> (u8, i32, i32, i32) {
         (
             self.v1_state().into(),
             self.v1_mode(),
             self.v1_size(),
             self.v1_mtime(),
         )
     }
 
     pub(crate) fn is_from_other_parent(&self) -> bool {
         self.flags.contains(Flags::WDIR_TRACKED | Flags::P2_INFO)
     }
 
     // TODO: other platforms
     #[cfg(unix)]
     pub fn mode_changed(
         &self,
         filesystem_metadata: &std::fs::Metadata,
     ) -> bool {
         let dirstate_exec_bit = (self.mode() as u32 & EXEC_BIT_MASK) != 0;
         let fs_exec_bit = has_exec_bit(filesystem_metadata);
         dirstate_exec_bit != fs_exec_bit
     }
 
     /// Returns a `(state, mode, size, mtime)` tuple as for
     /// `DirstateMapMethods::debug_iter`.
     pub fn debug_tuple(&self) -> (u8, i32, i32, i32) {
         (self.state().into(), self.mode(), self.size(), self.mtime())
     }
 }
 
 impl EntryState {
     pub fn is_tracked(self) -> bool {
         use EntryState::*;
         match self {
             Normal | Added | Merged => true,
             Removed => false,
         }
     }
 }
 
 impl TryFrom<u8> for EntryState {
     type Error = HgError;
 
     fn try_from(value: u8) -> Result<Self, Self::Error> {
         match value {
             b'n' => Ok(EntryState::Normal),
             b'a' => Ok(EntryState::Added),
             b'r' => Ok(EntryState::Removed),
             b'm' => Ok(EntryState::Merged),
             _ => Err(HgError::CorruptedRepository(format!(
                 "Incorrect dirstate entry state {}",
                 value
             ))),
         }
     }
 }
 
 impl From<EntryState> for u8 {
     fn from(val: EntryState) -> Self {
         match val {
             EntryState::Normal => b'n',
             EntryState::Added => b'a',
             EntryState::Removed => b'r',
             EntryState::Merged => b'm',
         }
     }
 }
 
 const EXEC_BIT_MASK: u32 = 0o100;
 
 pub fn has_exec_bit(metadata: &std::fs::Metadata) -> bool {
     // TODO: How to handle executable permissions on Windows?
     use std::os::unix::fs::MetadataExt;
     (metadata.mode() & EXEC_BIT_MASK) != 0
 }