[Request] [+- ] D11624: dirstate-v2: Change the representation of negative directory mtime
SimonSapin
phabricator at mercurial-scm.org
Mon Oct 11 20:32:01 UTC 2021
SimonSapin created this revision.
Herald added a reviewer: hg-reviewers.
Herald added a subscriber: mercurial-patches.
REVISION SUMMARY
Change it from how I previously thought Câs `timespec` works
to how it actually works. See code comments.
REPOSITORY
rHG Mercurial
BRANCH
default
REVISION DETAIL
https://phab.mercurial-scm.org/D11624
AFFECTED FILES
rust/hg-core/src/dirstate_tree/on_disk.rs
CHANGE DETAILS
diff --git a/rust/hg-core/src/dirstate_tree/on_disk.rs b/rust/hg-core/src/dirstate_tree/on_disk.rs
--- a/rust/hg-core/src/dirstate_tree/on_disk.rs
+++ b/rust/hg-core/src/dirstate_tree/on_disk.rs
@@ -185,8 +185,7 @@
/// In `0 .. 1_000_000_000`.
///
- /// This timestamp is later or earlier than `(seconds, 0)` by this many
- /// nanoseconds, if `seconds` is non-negative or negative, respectively.
+ /// This timestamp is after `(seconds, 0)` by this many nanoseconds.
nanoseconds: U32Be,
}
@@ -503,15 +502,33 @@
}
}
+const NSEC_PER_SEC: u32 = 1_000_000_000;
+
impl From<SystemTime> for Timestamp {
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 (secs, nanos) = match system_time.duration_since(UNIX_EPOCH) {
Ok(duration) => {
(duration.as_secs() as i64, 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();
- (-(negative.as_secs() as i64), negative.subsec_nanos())
+ let negative_secs = negative.as_secs() as i64;
+ let negative_nanos = negative.subsec_nanos();
+ if negative_nanos == 0 {
+ (-negative_secs, 0)
+ } else {
+ // For example if `system_time` was 4.3Â seconds before
+ // the Unix epoch we get a Duration that represents
+ // `(-4, -0.3)` but we want `(-5, +0.7)`:
+ (-1 - negative_secs, NSEC_PER_SEC - negative_nanos)
+ }
}
};
Timestamp {
@@ -525,10 +542,17 @@
fn from(timestamp: &'_ Timestamp) -> Self {
let secs = timestamp.seconds.get();
let nanos = timestamp.nanoseconds.get();
- if secs >= 0 {
+ if secs < 0 {
+ let (s_to_subtract, ns_to_subtract) = if nanos == 0 {
+ (-secs, 0)
+ } else {
+ // Example: `(-5, +0.7)` â `(-4, -0.3)`
+ // See `impl From<SystemTime> for Timestamp` above
+ (1 - secs, NSEC_PER_SEC - nanos)
+ };
+ UNIX_EPOCH - Duration::new(s_to_subtract as u64, ns_to_subtract)
+ } else {
UNIX_EPOCH + Duration::new(secs as u64, nanos)
- } else {
- UNIX_EPOCH - Duration::new((-secs) as u64, nanos)
}
}
}
To: SimonSapin, #hg-reviewers
Cc: mercurial-patches, mercurial-devel
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