Generate DateOnly and TimeOnly: Gen functions, auto-generation and attributes by xperiandri · Pull Request #488 · hedgehogqa/fsharp-hedgehog

xperiandri · 2026-10-10T12:36:19Z

Gen.auto<DateOnly> and Gen.auto<TimeOnly> throw today, so a property with a parameter of one of these types fails in every adapter:

[<Property>]
let ``a date and a time`` (date: DateOnly) (time: TimeOnly) = true
// System.ArgumentOutOfRangeException: Year, Month, and Day parameters describe an un-representable DateTime.
// System.ArgumentOutOfRangeException: Ticks must be between 0 and and TimeOnly.MaxValue.Ticks. (Parameter 'ticks')

Hedgehog has no generator for the two types, so auto-generation goes through their constructors, DateOnly(year, month, day) and TimeOnly(ticks), and passes arbitrary integers.

What this adds

Gen.dateOnly and Gen.timeOnly (Gen.DateTime.fs), from a Range, like Gen.dateTime and Gen.timeSpan. They generate over the day number and the ticks of the value, and sit next to Gen.timeSpan, in the block that is not compiled for Fable.
Gen.DateOnly and Gen.TimeOnly in Hedgehog.Linq.
Default generators, so that Gen.auto and the adapters generate both types without any setup:
- DateOnly: an exponential range around 2000-01-01 over the whole type, as for DateTime;
- TimeOnly: a linear range over the day. An exponential one would keep the times of half of all sizes within the first tenth of a second after midnight, because a day has 864 billion ticks.
[<DateOnly>] and [<TimeOnly>] in Hedgehog.Xunit and Hedgehog.NUnit, next to [<DateTime>] and [<DateTimeOffset>]: a minimum and a maximum, both included. Without arguments DateOnly generates within the 3650 days from 2000-01-01, the dates of the default range of [<DateTime>], and TimeOnly any time of day.

An attribute argument has to be a constant, so it cannot be a DateOnly or a TimeOnly. Both attributes therefore also take their range as integers; the constructor that takes the two values serves attributes that derive from them.

[<Property>]
let ``dates of 2024`` ([<DateOnly(2024, 1, 1, 2024, 12, 31)>] date: DateOnly) =
    date.Year = 2024

[<Property>]
let ``office hours`` ([<TimeOnly(9, 0, 17, 0)>] time: TimeOnly) =
    time.Hour >= 9 && time <= TimeOnly(17, 0)

Testing

Hedgehog.Tests: both generators stay inside their range, reach every value of a range of three values, and shrink to the origin of their range.
Hedgehog.Autogen.Tests: Gen.auto<DateOnly> and Gen.auto<TimeOnly>. Both tests fail on master with the exceptions above.
Hedgehog.Xunit.Tests.FSharp, Hedgehog.Xunit.Tests.CSharp and Hedgehog.NUnit.Tests.FSharp: the attributes with and without a range. The two xUnit suites also run a property whose DateOnly and TimeOnly parameters have no attribute.
dotnet build and dotnet test of the whole solution pass locally with SDK 8.0.416.

Notes

docs/xunit/attributes.md describes the two attributes. Its DateTime section shows [<DateTime(DateTime(2020, 1, 1), TimeSpan.FromDays(365))>], which does not compile for the same reason: an attribute argument has to be a constant. I left that section alone.
The MSTest adapter of Add Hedgehog.MSTest: Property attributes for MSTest 4 #487 has the same two attributes. There they generate over the day number and the ticks themselves, so that Add Hedgehog.MSTest: Property attributes for MSTest 4 #487 does not depend on this pull request; whichever of the two is merged second can switch them to Gen.dateOnly and Gen.timeOnly.

🤖 Generated with Claude Code

Gen.auto fails for both types: it builds a DateOnly through its (year, month, day) constructor and a TimeOnly through its ticks constructor with arbitrary integers, which throw ArgumentOutOfRangeException ("Year, Month, and Day parameters describe an un-representable DateTime", "Ticks must be between 0 and TimeOnly.MaxValue.Ticks"). A property with a parameter of one of these types therefore fails in every test framework adapter. Gen.dateOnly and Gen.timeOnly generate from a range, like Gen.dateTime and Gen.timeSpan, over the day number and the ticks of the value. They sit next to Gen.timeSpan, in the part that is not compiled for Fable. Hedgehog.Linq gets Gen.DateOnly and Gen.TimeOnly. DefaultGenerators uses them, so Gen.auto and the adapters generate both types: a DateOnly from an exponential range around 2000-01-01, as for DateTime, and a TimeOnly from a linear range over the day. An exponential range would keep the times of half of all sizes within the first tenth of a second after midnight, because a day has 864 billion ticks. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…Unit DateOnlyAttribute and TimeOnlyAttribute set the generator of one parameter, like DateTimeAttribute and DateTimeOffsetAttribute, from a minimum to a maximum, both included. Without arguments DateOnly generates within the 3650 days from 2000-01-01, the dates of DateTimeAttribute's default range, and TimeOnly any time of day. An attribute argument must be a constant, so it cannot be a DateOnly or a TimeOnly. Both attributes therefore also take their range as integers, [<DateOnly(2024, 1, 1, 2024, 12, 31)>] and [<TimeOnly(9, 0, 17, 0)>]; the constructor that takes the two values serves attributes that derive from these. The tests cover both adapters in F# and Hedgehog.Xunit in C#, including a property whose DateOnly and TimeOnly parameters have no attribute. The attribute documentation of Hedgehog.Xunit describes both attributes. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Copilot

🟢 Approval recommended

The implementations correctly preserve range bounds and shrink origins, with appropriate adapter and autogeneration coverage.

0 open findings

What changed in this PR

Adds first-class DateOnly and TimeOnly generation across Hedgehog’s F#, C#, autogeneration, xUnit, and NUnit APIs.

Changes:

Adds range-aware generators and LINQ wrappers.
Registers safe default autogenerators.
Adds adapter attributes, documentation, and comprehensive tests.

File	Description
`src/Hedgehog/Gen.DateTime.fs`	Implements both generators.
`src/Hedgehog/Linq/Gen.fs`	Exposes C# generator APIs.
`src/Hedgehog/Autogen/DefaultGenerators.fs`	Registers default generators.
`src/Hedgehog.Xunit/GenAttribute.Prelude.fs`	Adds xUnit attributes.
`src/Hedgehog.NUnit/GenAttribute.Prelude.fs`	Adds NUnit attributes.
`tests/Hedgehog.Tests/GenTests.fs`	Tests ranges and shrinking.
`tests/Hedgehog.Autogen.Tests/GenTests.fs`	Tests automatic generation.
`tests/Hedgehog.Xunit.Tests.FSharp/PropertyTests.fs`	Tests F# xUnit integration.
`tests/Hedgehog.Xunit.Tests.CSharp/AttributesTests.cs`	Tests C# xUnit integration.
`tests/Hedgehog.NUnit.Tests.FSharp/GenAttributePreludeTests.fs`	Tests NUnit integration.
`docs/xunit/attributes.md`	Documents the new attributes.

🧠 Review effort: Balanced

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The maintainer's reviews of 2026-10-10 changed several things the record describes, and it now says so where each belongs. The Hedgehog MSTest adapter (#43): the in-repository copy follows the coding guidelines of this repository, while the upstream pull request keeps upstream's style in a copy of its own, so a change of behaviour goes into both; an invocation that MSTest could not run stops the run instead of being shrunk; Odd and Even stay inside their range; DateOnly and TimeOnly get generators, upstream through hedgehogqa/fsharp-hedgehog#488. The open question of the adapter's code style is answered, with formatting and nullness checking still open. Collections (section 4): the shared collection functions of #47 that return voption and struct tuples, tested with properties in #50, and the rule of one module per pipeline of #49. Build (section 5): why FAKE's DotNet.test cannot run the test applications, and fsprojects/FAKE#2903, which adds DotNet.testMTP. The spec model (sections 6 and 16): EquatableArray and the ImmutableArray patterns are #48 and the model itself #42; the validator returns an ImmutableArray of struct errors. Golden baselines (section 13): a literal type provider was evaluated on the question asked in #46 and rejected, with the reasons. Tests (section 22): test category attributes sorted by name, Pascal-case assertion functions and ImmutableArray for shared test data. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The maintainer's reviews of 2026-10-10 changed several things the record describes, and it now says so where each belongs. The Hedgehog MSTest adapter (#43): the in-repository copy follows the coding guidelines of this repository, while the upstream pull request keeps upstream's style in a copy of its own, so a change of behaviour goes into both; an invocation that MSTest could not run stops the run instead of being shrunk; the cancellation token is checked after every invocation, whatever its outcome, which the automatic review of #50 asked for; Odd and Even stay inside their range; DateOnly and TimeOnly get generators, upstream through hedgehogqa/fsharp-hedgehog#488. The open question of the adapter's code style is answered, with formatting and nullness checking still open. Collections (section 4): the shared collection functions of #47 that return voption and struct tuples, tested with properties in #50, and the rule of one module per pipeline of #49. Build (section 5): why FAKE's DotNet.test cannot run the test applications, and fsprojects/FAKE#2903, which adds DotNet.testMTP. The spec model (sections 6 and 16): EquatableArray and the ImmutableArray patterns are #48 and the model itself #42; the validator returns an ImmutableArray of struct errors. Golden baselines (section 13): a literal type provider was evaluated on the question asked in #46 and rejected, with the reasons. Tests (section 22): test category attributes sorted by name, Pascal-case assertion functions and ImmutableArray for shared test data. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The maintainer's reviews of 2026-10-10 changed several things the record describes, and it now says so where each belongs. The Hedgehog MSTest adapter (#43): the in-repository copy follows the coding guidelines of this repository, while the upstream pull request keeps upstream's style in a copy of its own, so a change of behaviour goes into both; an invocation that MSTest could not run stops the run instead of being shrunk; the cancellation token is checked after every invocation, whatever its outcome, which the automatic review of #50 asked for; Odd and Even stay inside their range; DateOnly and TimeOnly get generators, upstream through hedgehogqa/fsharp-hedgehog#488. The open question of the adapter's code style is answered, formatting and nullness checking included: the two projects are formatted with Fantomas and build with nullness checking on, and only the verbatim port keeps upstream's settings. Collections (section 4): the shared collection functions of #47 that return voption and struct tuples, tested with properties in #50, and the rule of one module per pipeline of #49. Build (section 5): why FAKE's DotNet.test cannot run the test applications, and fsprojects/FAKE#2903, which adds DotNet.testMTP. The spec model (sections 6 and 16): EquatableArray and the ImmutableArray patterns are #48 and the model itself #42; the validator returns an ImmutableArray of struct errors. Golden baselines (section 13): a literal type provider was evaluated on the question asked in #46 and rejected, with the reasons. Tests (section 22): test category attributes sorted by name, in #51 with an instruction scoped to those files, Pascal-case assertion functions and ImmutableArray for shared test data. Two more answers of the same day: the Windows emulator lane of #45 runs weekly instead of nightly (section 2), and the shared collection functions of #47 are in the namespace FSharp.Azure.Cosmos instead of the global one (section 4). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Copilot

🟢 Approval recommended

The generators, integrations, documentation, and tests are consistent and no unresolved correctness issues were found.

0 open findings

🧠 Review effort: Balanced

…tribute Hedgehog 2.0.4 has no generator of the two types: `Gen.auto` calls a constructor of the type with integers that it generates, and the constructor refuses them. So a parameter of such a type, or of a type that holds one, needed `[<DateOnly>]`, `[<TimeOnly>]` or a generator of the test. hedgehogqa/fsharp-hedgehog#488 adds the two default generators to Hedgehog itself. Until a release has them, the adapter registers the same two for the parameters of a property: the configuration that a property starts from is `AutoGenConfig.propertyDefaults`, the defaults of Hedgehog and these generators. The configuration that a test names is merged over it as before, so a generator of the test still wins, and so does an attribute on the parameter. A date lies around 2000-01-01, further away the larger a case is. A time of day lies anywhere in the day, later the larger a case is. The suite has a test that fails as soon as Hedgehog generates the two types by itself: `propertyDefaults` goes then. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…ADR 0001 Hedgehog 2.0.4 cannot generate the two types, and hedgehogqa/fsharp-hedgehog#488 adds the generators upstream. Until a release has them, the adapter of this repository registers the same two for the parameters of a property (#43). The record of the adapter says so, and when the stand-in goes. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…tribute Hedgehog 2.0.4 has no generator of the two types: `Gen.auto` calls a constructor of the type with integers that it generates, and the constructor refuses them. So a parameter of such a type, or of a type that holds one, needed `[<DateOnly>]`, `[<TimeOnly>]` or a generator of the test. hedgehogqa/fsharp-hedgehog#488 adds the two default generators to Hedgehog itself. Until a release has them, the adapter registers the same two for the parameters of a property: the configuration that a property starts from is `AutoGenConfig.propertyDefaults`, the defaults of Hedgehog and these generators. The configuration that a test names is merged over it as before, so a generator of the test still wins, and so does an attribute on the parameter. A date lies around 2000-01-01, further away the larger a case is. A time of day lies anywhere in the day, later the larger a case is. The suite has a test that fails as soon as Hedgehog generates the two types by itself: `propertyDefaults` goes then. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Hedgehog.MSTest 1.0.0, the MSTest adapter of Hedgehog (hedgehogqa/fsharp-hedgehog#487), is released, so a test project references the package. Hedgehog 2.0.4 is the version that it depends on. Both get a central version, and the coverage report leaves out their assemblies, which a property test loads. The agent instructions list the two packages and say how a property test is written: a method of a [<TestClass>] type marked [<Property>], with generated parameters, never Property.check inside a [<TestMethod>]; an instance method that returns unit, Task or ValueTask and fails by throwing, because MSTest 4 rejects static methods and other return types and one such method fails the discovery of the whole assembly, which --list-tests shows before a run; that MSTest runs the test class and its [<TestInitialize>] and [<TestCleanup>] for every generated case and every shrink step; and that a failure reports a [<Recheck>] that replays it. They also say that Hedgehog 2.0.4 cannot generate DateOnly and TimeOnly, which hedgehogqa/fsharp-hedgehog#488 has merged and not released, so a parameter of such a type needs a generator of its own. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>