Export of internal Abseil changes.
-- f4e870453d02106c2685e0461816469a4704ad25 by Abseil Team <absl-team@google.com>: Expose TimeZone::NextTransition() and PrevTransition() now that we have absl::CivilSecond support in time.h. Note that these are for informational purposes only. General time code should not care when offset changes occur. PiperOrigin-RevId: 217177292 -- cfadd275c7333f7c27c4d682b9d167010d874e69 by Abseil Team <absl-team@google.com>: Import of CCTZ from GitHub. PiperOrigin-RevId: 217153577 -- 6ff5b8c61a1239b9c0478a7c62bcd2844b310307 by Jon Cohen <cohenjon@google.com>: Fix code examples in hash_testing.h. Includes random clang-format changes. PiperOrigin-RevId: 216898995 -- de124129d27f4627dabe193a10bf106a11783fba by Shaindel Schwartz <shaindel@google.com>: Add contribution guidelines describing how we decide whether to include an API in Abseil. PiperOrigin-RevId: 216886943 GitOrigin-RevId: f4e870453d02106c2685e0461816469a4704ad25 Change-Id: Ib9c6706f5bf931b71c0357bf1342053a3bee8ff7
This commit is contained in:
Abseil Team
Xiaoyi Zhang
parent
a00bdd176d
commit
5b70a8910b
6 changed files with 193 additions and 19 deletions
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@ -18,6 +18,53 @@ You generally only need to submit a CLA once, so if you've already submitted one
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(even if it was for a different project), you probably don't need to do it
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again.
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## Contribution Guidelines
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Potential contributors sometimes ask us if the Abseil project is the appropriate
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home for their utility library code or for specific functions implementing
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missing portions of the standard. Often, the answer to this question is "no".
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We’d like to articulate our thinking on this issue so that our choices can be
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understood by everyone and so that contributors can have a better intuition
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about whether Abseil might be interested in adopting a new library.
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### Priorities
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Although our mission is to augment the C++ standard library, our goal is not to
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provide a full forward-compatible implementation of the latest standard. For us
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to consider a library for inclusion in Abseil, it is not enough that a library
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is useful. We generally choose to release a library when it meets at least one
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of the following criteria:
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* **Widespread usage** - Using our internal codebase to help gauge usage, most
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of the libraries we've released have tens of thousands of users.
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* **Anticipated widespread usage** - Pre-adoption of some standard-compliant
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APIs may not have broad adoption initially but can be expected to pick up
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usage when it replaces legacy APIs. `absl::from_chars`, for example,
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replaces existing code that converts strings to numbers and will therefore
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likely see usage growth.
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* **High impact** - APIs that provide a key solution to a specific problem,
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such as `absl::FixedArray`, have higher impact than usage numbers may signal
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and are released because of their importance.
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* **Direct support for a library that falls under one of the above** - When we
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want access to a smaller library as an implementation detail for a
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higher-priority library we plan to release, we may release it, as we did
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with portions of `absl/meta/type_traits.h`. One consequence of this is that
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the presence of a library in Abseil does not necessarily mean that other
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similar libraries would be a high priority.
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### API Freeze Consequences
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Via the
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[Abseil Compatibility Guidelines](https://abseil.io/about/compatibility), we
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have promised a large degree of API stability. In particular, we will not make
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backward-incompatible changes to released APIs without also shipping a tool or
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process that can upgrade our users' code. We are not yet at the point of easily
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releasing such tools. Therefore, at this time, shipping a library establishes an
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API contract which is borderline unchangeable. (We can add new functionality,
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but we cannot easily change existing behavior.) This constraint forces us to
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very carefully review all APIs that we ship.
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## Coding Style
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To keep the source consistent, readable, diffable and easy to merge, we use a
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@ -90,7 +90,7 @@ namespace absl {
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// template <typename H>
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// friend H AbslHashValue(H state, Bad2 x) {
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// // Uses a and b.
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// return H::combine(x.a, x.b);
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// return H::combine(std::move(state), x.a, x.b);
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// }
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// friend bool operator==(Bad2 x, Bad2 y) {
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// // Only uses a.
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@ -107,7 +107,7 @@ namespace absl {
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// template <typename H>
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// friend H AbslHashValue(H state, Bad3 x) {
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// // Only uses a.
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// return H::combine(x.a);
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// return H::combine(std::move(state), x.a);
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// }
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// friend bool operator==(Bad3 x, Bad3 y) {
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// // Uses a and b.
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@ -123,19 +123,21 @@ namespace absl {
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// int *p, size;
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// template <typename H>
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// friend H AbslHashValue(H state, Bad4 x) {
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// return H::combine_range(x.p, x.p + x.size);
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// return H::combine_contiguous(std::move(state), x.p, x.p + x.size);
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// }
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// friend bool operator==(Bad4 x, Bad4 y) {
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// return std::equal(x.p, x.p + x.size, y.p, y.p + y.size);
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// // Compare two ranges for equality. C++14 code can instead use std::equal.
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// return absl::equal(x.p, x.p + x.size, y.p, y.p + y.size);
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// }
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// };
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//
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// An easy solution to this is to combine the size after combining the range,
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// like so:
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// template <typename H>
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// friend H AbslHashValue(H state, Bad4 x) {
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// return H::combine(H::combine_range(x.p, x.p + x.size), x.size);
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// }
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// template <typename H>
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// friend H AbslHashValue(H state, Bad4 x) {
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// return H::combine(
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// H::combine_contiguous(std::move(state), x.p, x.p + x.size), x.size);
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// }
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//
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template <int&... ExplicitBarrier, typename Container>
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ABSL_MUST_USE_RESULT testing::AssertionResult
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@ -227,7 +229,8 @@ VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals) {
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// Now we verify that AbslHashValue is also correctly implemented.
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for (const auto& c : classes) {
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// All elements of the equivalence class must have the same hash expansion.
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// All elements of the equivalence class must have the same hash
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// expansion.
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const SpyHashState expected = c[0].expand();
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for (const Info& v : c) {
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if (v.expand() != v.expand()) {
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@ -285,7 +288,7 @@ struct TypeSet {
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};
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template <typename... T>
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struct MakeTypeSet : TypeSet<>{};
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struct MakeTypeSet : TypeSet<> {};
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template <typename T, typename... Ts>
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struct MakeTypeSet<T, Ts...> : MakeTypeSet<Ts...>::template Insert<T>::type {};
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@ -346,8 +349,7 @@ template <int&..., typename Container, typename Eq>
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ABSL_MUST_USE_RESULT testing::AssertionResult
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VerifyTypeImplementsAbslHashCorrectly(const Container& values, Eq equals) {
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return hash_internal::VerifyTypeImplementsAbslHashCorrectly(
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hash_internal::ContainerAsVector<Container>::Do(values),
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equals);
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hash_internal::ContainerAsVector<Container>::Do(values), equals);
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}
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template <int&..., typename T>
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@ -991,15 +991,17 @@ TEST(MakeTime, SysSecondsLimits) {
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tp = convert(civil_second::min(), west);
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EXPECT_EQ(time_point<absl::time_internal::cctz::seconds>::min(), tp);
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// Checks that "tm_year + 1900", as used by the "libc" implementation,
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// can produce year values beyond the range on an int without overflow.
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if (sizeof(std::time_t) >= 8) {
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// Checks that "tm_year + 1900", as used by the "libc" implementation,
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// can produce year values beyond the range on an int without overflow.
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#if defined(_WIN32) || defined(_WIN64)
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// localtime_s() and gmtime_s() don't believe in years past 3000.
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// localtime_s() and gmtime_s() don't believe in years past 3000.
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#else
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const time_zone libc_utc = LoadZone("libc:UTC");
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tp = convert(civil_year(year_t{2147483648}), libc_utc);
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EXPECT_EQ("2147483648-01-01T00:00:00+00:00", format(RFC3339, tp, libc_utc));
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const time_zone libc_utc = LoadZone("libc:UTC");
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tp = convert(civil_year(year_t{2147483648}), libc_utc);
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EXPECT_EQ("2147483648-01-01T00:00:00+00:00", format(RFC3339, tp, libc_utc));
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#endif
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}
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}
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TEST(NextTransition, UTC) {
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@ -176,6 +176,20 @@ inline int MapWeekday(const cctz::weekday& wd) {
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return 1;
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}
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bool FindTransition(const cctz::time_zone& tz,
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bool (cctz::time_zone::*find_transition)(
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const cctz::time_point<cctz::seconds>& tp,
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cctz::time_zone::civil_transition* trans) const,
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Time t, TimeZone::CivilTransition* trans) {
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// Transitions are second-aligned, so we can discard any fractional part.
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const auto tp = unix_epoch() + cctz::seconds(ToUnixSeconds(t));
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cctz::time_zone::civil_transition tr;
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if (!(tz.*find_transition)(tp, &tr)) return false;
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trans->from = CivilSecond(tr.from);
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trans->to = CivilSecond(tr.to);
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return true;
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}
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} // namespace
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//
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@ -366,6 +380,14 @@ absl::TimeZone::TimeInfo TimeZone::At(CivilSecond ct) const {
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return ti;
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}
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bool TimeZone::NextTransition(Time t, CivilTransition* trans) const {
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return FindTransition(cz_, &cctz::time_zone::next_transition, t, trans);
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}
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bool TimeZone::PrevTransition(Time t, CivilTransition* trans) const {
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return FindTransition(cz_, &cctz::time_zone::prev_transition, t, trans);
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}
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//
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// Conversions involving time zones.
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//
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@ -886,7 +886,7 @@ class TimeZone {
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struct TimeInfo {
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enum CivilKind {
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UNIQUE, // the civil time was singular (pre == trans == post)
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SKIPPED, // the civil time did not exist (pre => trans > post)
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SKIPPED, // the civil time did not exist (pre >= trans > post)
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REPEATED, // the civil time was ambiguous (pre < trans <= post)
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} kind;
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Time pre; // time calculated using the pre-transition offset
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@ -925,6 +925,44 @@ class TimeZone {
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// // nov06.post is 2011-11-06 01:15:00 -0800
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TimeInfo At(CivilSecond ct) const;
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// TimeZone::NextTransition()
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// TimeZone::PrevTransition()
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//
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// Finds the time of the next/previous offset change in this time zone.
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//
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// By definition, `NextTransition(t, &trans)` returns false when `t` is
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// `InfiniteFuture()`, and `PrevTransition(t, &trans)` returns false
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// when `t` is `InfinitePast()`. If the zone has no transitions, the
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// result will also be false no matter what the argument.
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//
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// Otherwise, when `t` is `InfinitePast()`, `NextTransition(t, &trans)`
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// returns true and sets `trans` to the first recorded transition. Chains
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// of calls to `NextTransition()/PrevTransition()` will eventually return
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// false, but it is unspecified exactly when `NextTransition(t, &trans)`
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// jumps to false, or what time is set by `PrevTransition(t, &trans)` for
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// a very distant `t`.
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//
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// Note: Enumeration of time-zone transitions is for informational purposes
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// only. Modern time-related code should not care about when offset changes
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// occur.
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//
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// Example:
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// absl::TimeZone nyc;
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// if (!absl::LoadTimeZone("America/New_York", &nyc)) { ... }
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// const auto now = absl::Now();
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// auto t = absl::InfinitePast();
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// absl::TimeZone::CivilTransition trans;
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// while (t <= now && nyc.NextTransition(t, &trans)) {
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// // transition: trans.from -> trans.to
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// t = nyc.At(trans.to).trans;
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// }
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struct CivilTransition {
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CivilSecond from; // the civil time we jump from
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CivilSecond to; // the civil time we jump to
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};
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bool NextTransition(Time t, CivilTransition* trans) const;
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bool PrevTransition(Time t, CivilTransition* trans) const;
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template <typename H>
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friend H AbslHashValue(H h, TimeZone tz) {
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return H::combine(std::move(h), tz.cz_);
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@ -1135,4 +1135,67 @@ TEST(Time, LegacyDateTime) {
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EXPECT_EQ("2014-10-29 22:58:59", absl::FormatTime(ymdhms, t, utc));
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}
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TEST(Time, NextTransitionUTC) {
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const auto tz = absl::UTCTimeZone();
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absl::TimeZone::CivilTransition trans;
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auto t = absl::InfinitePast();
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EXPECT_FALSE(tz.NextTransition(t, &trans));
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t = absl::InfiniteFuture();
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EXPECT_FALSE(tz.NextTransition(t, &trans));
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}
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TEST(Time, PrevTransitionUTC) {
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const auto tz = absl::UTCTimeZone();
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absl::TimeZone::CivilTransition trans;
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auto t = absl::InfiniteFuture();
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EXPECT_FALSE(tz.PrevTransition(t, &trans));
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t = absl::InfinitePast();
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EXPECT_FALSE(tz.PrevTransition(t, &trans));
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}
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TEST(Time, NextTransitionNYC) {
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const auto tz = absl::time_internal::LoadTimeZone("America/New_York");
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absl::TimeZone::CivilTransition trans;
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auto t = absl::FromCivil(absl::CivilSecond(2018, 6, 30, 0, 0, 0), tz);
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EXPECT_TRUE(tz.NextTransition(t, &trans));
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EXPECT_EQ(absl::CivilSecond(2018, 11, 4, 2, 0, 0), trans.from);
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EXPECT_EQ(absl::CivilSecond(2018, 11, 4, 1, 0, 0), trans.to);
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t = absl::InfiniteFuture();
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EXPECT_FALSE(tz.NextTransition(t, &trans));
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t = absl::InfinitePast();
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EXPECT_TRUE(tz.NextTransition(t, &trans));
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if (trans.from == absl::CivilSecond(1918, 03, 31, 2, 0, 0)) {
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// It looks like the tzdata is only 32 bit (probably macOS),
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// which bottoms out at 1901-12-13T20:45:52+00:00.
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EXPECT_EQ(absl::CivilSecond(1918, 3, 31, 3, 0, 0), trans.to);
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} else {
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EXPECT_EQ(absl::CivilSecond(1883, 11, 18, 12, 3, 58), trans.from);
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EXPECT_EQ(absl::CivilSecond(1883, 11, 18, 12, 0, 0), trans.to);
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}
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}
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TEST(Time, PrevTransitionNYC) {
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const auto tz = absl::time_internal::LoadTimeZone("America/New_York");
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absl::TimeZone::CivilTransition trans;
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auto t = absl::FromCivil(absl::CivilSecond(2018, 6, 30, 0, 0, 0), tz);
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EXPECT_TRUE(tz.PrevTransition(t, &trans));
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EXPECT_EQ(absl::CivilSecond(2018, 3, 11, 2, 0, 0), trans.from);
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EXPECT_EQ(absl::CivilSecond(2018, 3, 11, 3, 0, 0), trans.to);
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t = absl::InfinitePast();
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EXPECT_FALSE(tz.PrevTransition(t, &trans));
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t = absl::InfiniteFuture();
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EXPECT_TRUE(tz.PrevTransition(t, &trans));
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// We have a transition but we don't know which one.
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}
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} // namespace
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Reference in a new issue