Fix | Write DateOnly instances to sql_variant columns of table-valued parameters as date values

[edwardneal]

Description

This builds on #4294, and handles the only other issue I saw while investigating #3934.

If a user-defined table type exists with a column of type sql_variant, client applications can insert a DateOnly instance into this. It's supposed to be sent with a type of date, but is actually sent as a datetime.

Besides a point around correctness, it presents an issue when sending DateOnly instances which are valid values for date but not for datetime: these values overflow.

This PR fixes the issue, transporting all DateOnly instances with the date type on modern .NET. On .NET Framework, there's no DateOnly type - and thus there's no way for the client to encapsulate a date value within a sql_variant column.

@ErikEJ, this covers the only other way to write DateOnly instances to SQL Server and should hopefully completely close #3934. SqlClient will continue to read DateTime instances by default, but this is needed for backwards compatibility purposes.

NB: similar issues also exist with TimeOnly instances. TdsParser assumes that only TimeSpan instances will be written as times, so there are failures to cast in a few different places.

Issues

Builds on #4294. Possible resolution to #3934.

Testing

#4294 added the relevant tests, with an exemption carved out for this use case. I've removed the exemption and verified that it covers the test case.

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[ErikEJ]

LGTM

[cheenamalhotra]

/azp run

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[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.64%. Comparing base (fdebcd2) to head (226969c).
⚠️ Report is 66 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/Microsoft/Data/SqlClient/Server/ValueUtilsSmi.cs	9.09%	20 Missing ⚠️
...c/Microsoft/Data/SqlClient/Server/SqlDataRecord.cs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4439      +/-   ##
==========================================
- Coverage   65.83%   62.64%   -3.20%     
==========================================
  Files         287      283       -4     
  Lines       43763    66949   +23186     
==========================================
+ Hits        28812    41938   +13126     
- Misses      14951    25011   +10060     

Flag	Coverage Δ
CI-SqlClient	?
PR-SqlClient-Project	62.64% <11.11%> (?)

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[benrr101]

Small change but seems pretty important!

[Copilot]

Pull request overview

This PR addresses a correctness issue when sending DateOnly values into sql_variant columns in table-valued parameters (TVPs): the value was being transported as datetime rather than date, which can overflow for DateOnly min/max values and yields an incorrect base type.

Changes:

• Updates TVP/SMI value-setting logic so DateOnly written to sql_variant is transported with base type date (modern .NET only).
• Relaxes variant metadata assertions to allow SqlDbType.Date where variant-type metadata is tracked.
• Updates manual variant tests to remove the prior overflow/“datetime” exemptions now that the scenario should succeed.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/ParameterTest/DateTimeVariantTests.cs	Removes expected overflow exceptions / base-type overrides for DateOnly in sql_variant TVP scenarios.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Server/ValueUtilsSmi.cs	Routes DateOnly through date-specific variant metadata handling for TVP writes; also adjusts sql-value retrieval logic for SqlDbType.Date.
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Server/SqlRecordBuffer.cs	Allows SqlDbType.Date in the debug assertion for variant metadata.

[apoorvdeshmukh]

/azp run

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