Add GetUtcNow to ITimeSystem

[ejsmith]

Fixes #1700

[sebastienros]

Or since ITypeSystem currently doesn't provide the date/time, maybe it could expose TimeProvider (passed by ctor) so this would make mocking the time easier by reusing DefaultTimeSystem instead of creating a new class.

Let's see what @lahma thinks is best. Either way implementation is trivial.

[lahma]

I think the current implementation should suffice quite nicely. TimeProvider is a bit problematic as it's a NET 8 feature and would require separate NuGet dependency added to get the feature to older targets (https://www.nuget.org/packages/Microsoft.Bcl.TimeProvider). This is why I would implement the support on consumer code instead of the library (it's very limited set of features where Jint needs current time as you can see).

Maybe a test case would be a nice addition showcasing the new possibilities?

[lahma]

The TimeProvider uses DateTimeOffset as return value though: https://learn.microsoft.com/en-us/dotnet/api/system.timeprovider.getutcnow?view=net-8.0#system-timeprovider-getutcnow

The real use cases for Jint are for the timestamp I guess https://learn.microsoft.com/en-us/dotnet/api/system.timeprovider.gettimestamp?view=net-8.0#system-timeprovider-gettimestamp as we only need to subtract to get the different in milliseconds.

[sebastienros]

TimeProvider is a bit problematic as it's a NET 8 feature

No, it's been backported down to full framework. Will investigate why the doc says .NET 8 only.

[sebastienros]

Oh, different assemblies, yes, probably.

[ejsmith]

Yeah, might be nice to have the full TimeProvider available and could eventually be used to virtualize timers, timeouts and such as well as providing current time. I was just trying to keep this PR simple.

[ejsmith]

Added a test showing how to integrate TimeProvider

[lahma]

Jint is is using central package management so you need to add the new dependency to Directory.Packages.props in root folder and reference it without version number in csproj. Can you also change the return type in ITmeProvider to DateTimeOffset? I know it doesn't matter for UTC but if we would ever add the GetLocalNow() we would be interested in offset part to and the methods would have parity (also parity with TimeProvider)

[ejsmith]

@lahma I'm confused by the build error saying it can't target .NET 8. I didn't change any framework version. This test project was already targeting net8.0.

[lahma]

It's OK, macos runners are lagging behind with net8.0 support.

[lahma]

Looks good, thank you!

[ejsmith]

Thank you!