release-notes.md

Release notes

A listing of what each Nuget package version represents.

v5

5.2.1 - (2026-02-09)

Fix: Stop todo evaluation at given datetime.
(If a TODO had an RRULE without COUNT or UNTIL, IsCompleted() threw with ArgumentOutOfRangeException.)

5.2.0 - (2025-12-24)

Implemented BYDAY with offset and limiting behavior

The following RRULE cases are now implemented

1. YEARLY + BYMONTH + numeric BYDAY offsets. Pattern: FREQ=YEARLY;BYMONTH=6,9;BYDAY=2MO
2. YEARLY + numeric BYDAY without BYMONTH. Pattern: FREQ=YEARLY;BYDAY=20MO
3. YEARLY + BYMONTH + negative numeric BYDAY. Pattern: FREQ=YEARLY;BYMONTH=6,9;BYDAY=-1SU

5.1.4 - (2025-12-13)

Fix: Regression introduced in v5.1.3 affecting RRULE:FREQ=YEARLY when negative BYMONTHDAY or BYYEARDAY values are used. In certain combinations the evaluator could normalize negative positions incorrectly and skip valid occurrences (e.g., end‑of‑month or end‑of‑year instances). This has been fixed — please upgrade to v5.1.4.

Example of an affected rule (prior behavior could skip results):

DTSTART:20250101
RRULE:FREQ=YEARLY;BYYEARDAY=-1,1;BYMONTHDAY=-1,1

5.1.3 - (2025-12-01)

Fix: Correct handling RRULE:FREQ=YEARLY combined with BYMONTH and BYWEEKNO. The previous implementation could skip occurrences in some scenarios. Fix: Correct handling RRULE:FREQ=YEARLY when BYMONTH ist missing, e.g. RRULE:FREQ=YEARLY;INTERVAL=2;BYDAY=MO,TU. Now takes the month of DTSTART as a limiter.

5.1.2 - (2025-11-13)

• Chore: Mark classes and interfaces using EXRULE as obsolete. Reasoning: EXRULE is marked as deprecated in RFC 5545. Neither Google Calendar nor Microsoft Outlook/Exchange support it.
• Feat: CalDateTime.Add(Duration) for empty Durations. The methods gets called frequently during recurrence evaluation. Here it brings a performance improvement of about 10%.
• Fix: FREQ=WEEKLY rules that include BYMONTH were only including weeks that start inside the given months. This fix checks the end of the week also to see if any part of the week is inside the given months.

5.1.1 - (2025-10-06)

• Fix: CalendarEvents with RecurrenceId were not properly evaluated in some scenarios.
• Feat: RecurringComponents like CalendarEvent support RECURRENCE-ID with optional RANGE parameter for serialization and deserialization.
• Wiki: Updated articles about recurrence evaluation

5.1.0 - (2025-07-16)

• Fix: Exception for Blazor WebAssembly and Self-Contained Assemblies using FileVersionInfo
• Fix: GetOccurrences() NPE when returning a ToDo's occurrences that don't have a duration
• Fix: Evaluation of EXDATE when date-only while DTSTART is date-time
• Feat: Use UTF-8 Encoding without BOM by default in all serializers when writing to a stream. This is expected by most iCalendar consumers, including Outlook and Google Calendar.
• Fix: CalDateTime CTOR using ISO 8601 UTC string resolves to UTC
• Fix: GetOccurrences(periodStart) to also include ongoing occurrences (beginning before periodStart)
• Fix: GetOccurrences() not properly dealing with periodStart's timezone ID

5.0.0 GA - (2025-06-17)

• Breaking: Remove redundant Equals and GetHashCode implementations in #810
• Breaking: Occurrence.Period is determined by StartTime and Duration only in #808
• Update package versions in #813 which includes NodaTime version 3.2.2
• Fix: Period.CollidesWith calculation in #812
• Added a Migration Guide for v4 to v5 to the wiki
• Update the list of API Changes from v4 to v5 in the wiki
• Publish v5.0.0 GA

5.0.0-pre.43 - (2025-05-21)

• Breaking: Enable NRT project wide in #769, #771, #772, #778, #786. NuGet Packages are now published with NRT enabled.
• Update license.md in #773
• EvaluationOptions: Fix off-by-one issue of MaxUnmatchedIncrementsLimit #775
• RecurrencePatternEvaluator: Modernize some evaluation code in #783
• Breaking: Evaluation: Remove periodEnd param from GetOccurrences et al in #781. To limit the elements, it's recommended to used CollectionExtensions.TakeWhileBefore (see below), or simple TakeWhile.
• Implement CollectionExtensions.TakeWhileBefore extensions in #796. This can e.g. be used on enumerations from GetOccurrences methods
• Evaluation: Raise EvaluationOutOfRangeException if year 10k is hit during evaluation in #785
• Remove unnecessary null checks in #790
• Breaking: Refactor handling of FREQ in recurrence pattern in #789. Removed FrequencyType.None from enum FrequencyType
• Breaking: Remove GroupedListEnumerator in #793 (Different solution made it redundant).
• Enable CA1305 warnings and fix them in #794
• Fix for serialization of property parameters: CalendarComponent.AddProperty adds the CalendarProperty in #801
• Breaking: Feature: Serialize multiple categories and resources to one line in #803 and #804

5.0.0-pre.42 - (2025-04-12)

• Fix incorrect handling of UNTIL if falling into DST change and some related improvements in #738
• Fix: Minor NRT warnings with Recurrence in #743
• Fix: Benchmarks in #746
• Replace DateTime with CalDateTime in RecurrencePatternEvaluator and related code in #742
• Evaluation: Make MaxIncrementCount configurable in #750
• Fix issue with BYWEEKNO=1 where UNTIL lies in the year prior to the year of the week of the last occurrence. in #752
• Remove IServiceProvider in #753
• Update PRODID and VERSION property handling in #748
• Enhance RecurrencePatternSerializer in #758
• Evaluation: Avoid dependency on local culture settings. in #759
• Change DateTime method args to CalDateTime in #761
• Enable NRT in #762, #763, #764, #765. Note: The current packages are created with NRT disabled, The v5 final release will be fully NRT compliant.
• Fix positive/nagative args in Duration CTOR in #767

5.0.0-pre.41 - (2025-02-20)

• Make the time zone resolver plugable
• Make CalendarEvent.EffectiveDuration and some conversion functions public.
• Fix: Incorrect expansion behaviour after BYWEEKNO

5.0.0-pre.40 - (2025-02-15)

• Fix: Derive correct file and assembly version from package version in #726
• Fix inverted limiting behavior of BYMONTHDAY by @minichma in #730

5.0.0-pre.39 - (2025-02-12)

• This is the first public pre-release of the next major version of Ical.Net. It's an extensive rewrite of the library, with a focus on performance, correctness and usability. All issues reported in prior versions have been addressed, and the library has been thoroughly tested, also using the libical test suite.
• We strongly recommend using the pre-release packages, as they are more stable and feature-complete than the v4.x versions.
• Feedback is highly appreciated.
• Breaking changes from v4 are currently listed here.

v4

• 4.3.1 - (2024-10-14)
  • Update Ical.Net.csproj to use NodaTime 3.2.0 instead of 3.1.12. NodaTime v3.2.0 which brings some welcome changes
  • Replace Ical.Net.nuspec with Directory.Build.props
  • Remove unnecessary nuget dependencies, so NodaTime is again the only one
• 4.3.0 - (2024-10-13)
  • Update the repository from fork laget.se/ical net
  • • Remove net5.0 as target framework from all projects
  • Merged a few pull requests that fixes a few bugs
    • #584, #579, #571, #528, #525, #471, #470, #443
  • Update CI workflows publish.yml and tests.yml
  • Update ProdId constant and NodaTime package version
  • Add back assembly signing to projects and include strong name key
  • Add class RegexDefaults and update all Regex with RegexDefaults.Timeout which is set to 200 milliseconds
• 4.2.0 - (2021-04-10) - Many bugbixes from the community
  • Fix infinite loop with MaxDate for GetOccurrences #364
  • Deserializes STANDARD and DAYLIGHT timezone infos #420
  • BYWEEKNO & BYMONTHNO fix for ISO-8601 formatting #463
  • Fixed bug where changing a property value appended the value instead of clearing it. #450
  • Fixed IsActive regression #449
  • Fixed bug where ordering of week numbers mattered for equality #513
  • Target netstandard20 and net50, unified build targets
  • Updated to NodaTime 3 and netcoreapp3.1 for unit tests (later changed to net50) #449
• 4.1.11 - (2019-03-21) - Add some conditional debug symbols so VSTS doesn't choke on strong-named assemblies. Thanks, eriknuds #442
• 4.1.10 - (2019-01-31) - Strong-named assemblies. Thanks, josteink #159
• 4.1.9 - (2018-07-18) - Associate attachments with their events when VALUE is BINARY. Without the association, parameters such as FMTTYPE would be lost. PR 411
• 4.1.8 - (2018-06-12) - PRODID and VERSION are unconditionally set when serializing a calendar so as not to mislead consumers about where the serialized output came from. Previous behavior would use the values that came from deserialization. #403
• 4.1.6 - (2018-06-01) - Target net46 instead of net45. It seems that System.Reflection.TypeExtensions, doesn't support framework versions below 4.6. Bummer.
• 4.1.5 - (2018-05-28)
  • Target net45 instead of net46 which opens up the applications that can consume the latest version! #392
  • NodaTime doesn't specify an end times for time zones which don't observe DST (such as America/Phoenix). We need to handle unbounded end times. #378
  • Better null handling for CalDateTimes. #372
• 4.1.4 - (2018-05-24) - #392. .NET Standard (still) doesn't play nicely with .NET Framework applications, so I have also targeted .NET 4.6 (net46). As a consequence of that, I had to downgrade System.Reflection.TypeExtensions to 4.1.0, because the original targeted version (4.3.0) was retargeted as netstandard2.0, rendering it incompatible with a netstandard1.3 library.
• 4.1.2 - (2018-05-21) - #388. Bugfix: Specifying a time zone identifier in the CalDateTime constructor should override the backing DateTime's Kind property. If no time zone identifier is specified, then the Kind property shouldn't be changed.
• 4.1.1 - (2018-05-21) - #387. Bugfix: Calling CalDateTime.AsUtc caches the UTC time, but the cache was not being reset if the TzId property changed.
• 4.1.0/4.0.7 - (2018-05-15) - #383. Add a read-only AsDateTimeOffset property to IDateTime. Add a few docs to RecurrencePattern.
• 4.0.6 - (2017-11-28) - #344. Fix the VERSION property so it's 2.0 as RFC-5545 requires.
• 4.0.4 PR 341. Cache the UTC representation for CalDateTimes. This results in a 12-16% reduction in unit test runtime.
• 4.0.3 #337. Fixed a bug in SimpleDeserializer where tab characters (\t) were excluded from regex match.
• 4.0.1 #335. Technically this should be 5.0, but given 4.0.0 only has 24 downloads, I've just done a minor version bump.
  • Moved everything from Ical.Net.Collections into the Ical.Net assembly.
  • Updated the PRODID stamp to say 4.0.
  • Fixed a bug with a missing nuget dependency
• 4.0.0:
  • DateTimeKind is preserved during serialization round trips. Z suffixed (i.e. UTC) DATE-TIMEs produce a DateTimeKind.Utc, and everything else produces a DateTimeKind.Local. Similarly, when creating CalDateTimes with ambiguous timezones, the DateTimeKind is examined in an attempt to infer whether it's a UTC time or not. In order of importance, the way of determining DateTimeKind is: time zone id, DateTimeKind on the incoming DateTime, and then a fallback. This should improve interop with other ical libraries like Telerik. #331
  • RRULE's UNTIL property is now inclusive, and doesn't rely on UTC time comparisons. #320
  • CalDateTime.ToTimeZone produces the correct local time #330
  • VEVENT status should be uppercase during serialization. A subtle (but breaking) change, necessitating a major version bump. #318
  • VTIMEZONEs are once again serialized, this time pulling historic time zone data from NodaTime -- thanks beriniwlew! PR 304
  • Entry points are now consolidated into the right places, and make sense:
    • CalendarCollection.Load() loads a CalendarCollection
    • Calendar.Load loads a Calendar.
    • CalendarComponent.Load() loads whatever type you're looking for.
  • The ANTLR-based parser is gone. chescock's SimpleDeserializer is used everywhere.

v3

• 3.0.15: .NET Standard version (aka v3 aka net-core) is missing System.Reflection.TypeExtensions dependency. #326
• 3.0.14: .NET Standard version (aka v3 aka net-core) is missing System.Runtime.Serialization.Primitives dependency. #324
• 3.0.13: DTSTART is not required for VTODO components. PR 322
• 3.0.12: Several improvements rolled up:
  • CalendarEvent now considers Summary and Description for equality and hashing. PR 309.
  • Protection against InvalidOperationExceptions in some collections usage scenarios PR 312
  • Normalized Journal implementation. PR 310
• 3.0.11-net-core-beta: Targeting netstandard1.3 and net46
• 3.0.10-net-core-beta: Reverts a change made in 3.0.3 which allowed UTC timestamps to specify TZID=UTC instead of being suffixed with Z. The spec requires Z suffixes, and broke many applications, including Outlook. #263
• 3.0.9-net-core-beta: Bugfixes: PeriodList now fully implements IList<Period>. Keep data structures in sync in GroupedList.Remove() #253. Fix for StackOverflow exception #257. UnitTests can now be run in VS test runner!
• 3.0.8-net-core-alpha: Bugfix: Better CalDateTime equality and hashing, because time zones matter. #275
• 3.0.7-net-core-alpha: Bugfix: Fixed a small ordering bug when evaluating EXDATEs and RDATEs #275
• 3.0.6-net-core-alpha: Bugfix: CalendarEvent's Equals() and GetHashCode() were buggy in that they did not consider RecurrenceDates and ExceptionDates properly. Both methods treated these properties as if they were a single collection. Now they are normalized by time zone when before determining whether complete set of RDATEs or EXDATEs are the same. #275
• 3.0.4-net-core-alpha: CalendarEvent's Equals() and GetHashCode() methods were asymmetric. Both now consider Attachments. In addition, several calendar components did not implement Equals() and GetHashCode(), namely Journal and Todo. They both delegate to RecurringComponent for the properties owned by that parent object, and extend the methods for the child properties that they respectively own. #271
• 3.0.3-net-core-alpha: Bringing in 2.2.34's changes: serializing EXDATEs and RDATEs now includes time zone information when specified. UTC timestamps are now allowed to be specified either in Z-suffixed form (which was mandatory before), OR explicitly with a time zone id (TZID=UTC). This allows greater interop with third-party libraries like Telerik's RadSchedule. #259 PeriodList now implements IList<Period>.
• 3.0.2-net-core-alpha: Fix nuspec file to declare NodaTime as dependency
• 3.0.1-alpha: Initial publishing of .NET Core release

v2

• 2.3.6 - (2019-01-30) - Strong-named assemblies. Thanks, josteink #159
• 2.3.5: VTIMEZONEs are once again serialized, this time pulling historic time zone data from NodaTime -- thanks beriniwlew! PR 304
• 2.3.4: DTSTART is not required for VTODO components. PR 322
• 2.3.3: Several improvements rolled up:
  • Event now considers Summary and Description for equality and hashing. PR 309.
  • Protection against InvalidOperationExceptions in some collections usage scenarios PR 312
  • Normalized Journal implementation. PR 310
• 2.3.2: Reverts a change made in 2.2.34 which allowed UTC timestamps to specify TZID=UTC instead of being suffixed with Z. The spec requires Z suffixes, and broke many applications, including Outlook. #263
• 2.3.0: PeriodList now implements IList #280
• 2.2.39: Bugfix: Better CalDateTime equality and hashing, because time zones matter. #275
• 2.2.38: Bugfix: Fixed a small ordering bug when evaluating EXDATEs and RDATEs #275
• 2.2.37: Bugfix: Event's Equals() and GetHashCode() were buggy in that they did not consider RecurrenceDates and ExceptionDates properly. Both methods treated these properties as if they were a single collection. Now they are normalized by time zone when before determining whether complete set of RDATEs or EXDATEs are the same. #275
• 2.2.35: Bugfix: Event's Equals() and GetHashCode() methods were asymmetric. Both now consider Attachments. In addition, several calendar components did not implement Equals() and GetHashCode(), namely Journal and Todo. They both delegate to RecurringComponent for the properties owned by that parent object, and extend the methods for the child properties that they respectively own. #271
• 2.2.34: Serializing EXDATEs and RDATEs now includes time zone information when specified. UTC timestamps are now allowed to be specified either in Z-suffixed form (which was mandatory before), OR explicitly with a time zone id (TZID=UTC). This allows greater interop with third-party libraries like Telerik's RadSchedule. #259
• 2.2.33: Bugfix for #235 when years have 53 weeks. Contains a new deserializer that's twice as fast as the default ANTLR implementation, and several other (smaller) performance enhancements. This will become the default deserializer in a future release. PR 246, PR 247
• 2.2.31: .NET's UTC offset parsing semantics don't match the RFC (which allows for hhmmss UTC offsets), so I extended the offset serializer to account for these differences. (#102, #236)
• 2.2.30: Event.Resources is an IList again. Event.Resources wasn't being deserialized, so I have reverted back to an IList to fix this. Sorry everyone. I'm intentionally violating my own semver rules. In the future, I'll call version n+1 "vNext" so I can more freely rev the major version number.
• 2.2.29: Calling GetOccurrences() on a recurrable component should recompute the recurrence set. Specifying EXDATE values that don't have a TimeOfDay component should "black out" that day from a recurring component's StartTime.#223
• 2.2.25: Fix for Collection was modified exception, and better handling of recurrence ids when calling Calendar.GetOccurrences (#188) (#148)
• 2.2.24: Performance enhancement for solidus-prefixed time zones (#204).
• 2.2.23: Bugfix for culture for geographic location serialization. RFC-5545 requires coordinates to use decimal points, not commas, regardless of culture. Correct: 1.2345. Incorrect: 1,2345. (#202)
• 2.2.22: Bugfix for Event serialization that always changed the Duration to 0. Serialization shouldn't have side effects. (#199)

Changes weren't systematically tracked before 2.2.22.