[Repo Assist] Add PreferDateTimeOffset parameter to CsvProvider, JsonProvider, and XmlProvider

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🤖 This is an automated pull request from Repo Assist, an AI assistant for this repository.

Adds a PreferDateTimeOffset static parameter (default: false) to CsvProvider, JsonProvider, and XmlProvider, addressing the long-standing requests in #1100 and #1072.

Closes #1100
Closes #1072

What this does

// Before: "2023-06-15T10:30:00" inferred as DateTime
type MyData = CsvProvider<"data.csv">

// After: "2023-06-15T10:30:00" inferred as DateTimeOffset (with local UTC offset)
type MyData = CsvProvider<"data.csv", PreferDateTimeOffset=true>

When PreferDateTimeOffset=true, all date-time columns/fields that would normally be inferred as DateTime are instead inferred as DateTimeOffset. Values already containing an explicit timezone offset (e.g., "2023-06-15T10:30:00+05:30") are already inferred as DateTimeOffset regardless of this flag.

Implementation

The change is a post-inference rewrite: after structural type inference, a tree-walking transform replaces DateTime → DateTimeOffset throughout the inferred type. No runtime changes are needed because TextRuntime.ConvertDateTimeOffset already has a fallback path that converts DateTime-like strings to DateTimeOffset using the local offset.

Files changed

• StructuralInference.fs: Two new internal helpers:
  • upgradeToDateTimeOffset — walks an InferedType tree, replacing DateTime → DateTimeOffset
  • upgradeToDateTimeOffsetPrimitiveProperty — CSV-specific version for PrimitiveInferedProperty
• CsvProvider.fs: New PreferDateTimeOffset static parameter (index 20); upgrade applied after the net6/DateOnly downgrade step
• JsonProvider.fs: New PreferDateTimeOffset static parameter (index 15); upgrade applied after the net6/DateOnly downgrade step
• XmlProvider.fs: New PreferDateTimeOffset static parameter (index 14); upgrade applied after the net6/DateOnly downgrade step
• TypeProviderInstantiation.fs: PreferDateTimeOffset field added to CsvProviderArgs, XmlProviderArgs, JsonProviderArgs
• RELEASE_NOTES.md: Updated

Test Status

• ✅ FSharp.Data.DesignTime builds (netstandard2.0 + net8.0)
• ✅ Core tests: 2846/2847 pass (1 pre-existing network test blocked by sandbox)
• ⚠️ DesignTime signature tests: 436/487 fail — this is a pre-existing failure on main unrelated to this PR (verified by running tests on unmodified main with same result)

Notes

• Only CsvProvider, JsonProvider, and XmlProvider are covered (HtmlProvider uses a different internal path that can be added in a follow-up)
• PreferDateTimeOffset and PreferDateOnly are orthogonal: DateOnly values stay as DateOnly even when PreferDateTimeOffset=true
• Default is false for full backward compatibility

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[dsyme]

I'm not a fan of this approach, we should really be plumbing these flags down into inference and making the conversions at the leaves rather than patching things up afterwards

[dsyme]

This way of doing PreferDateOnly needs some work. Since PreferDateOnly is not the default, we should not be introducing DateOnly only to remove them again

We should clean this up in main before taking this feature

[dsyme]

/repo-assist Update the docs

[github-actions]

Commit pushed: f311d7b

Generated by Repo Assist

[github-actions]

🤖 This is an automated response from Repo Assist.

I've added documentation for PreferDateTimeOffset to the following files:

• docs/library/CsvProvider.fsx — Added mention in the inline comment, the narrative text about date inference, the "Controlling the column types" section, and a new "### DateTimeOffset" subsection.
• docs/library/JsonProvider.fsx — Extended the "Inferring date types" section to describe PreferDateTimeOffset.
• docs/library/XmlProvider.fsx — Added a new "## Inferring date types" section covering DateTime, DateTimeOffset, PreferDateOnly, and PreferDateTimeOffset.
• docs/library/TypeInference.fsx — Updated the date/time table to include a PreferDateTimeOffset row, added explanatory text, and added it to the "Summary of Inference-Control Parameters" table.

Generated by Repo Assist for issue #1668

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