Fix precision of rescaled zero decimal parameters

[saurabh500]

Description

Fix the 7.1.0 regression where CLR 0m fails with ArgumentException when sent as a decimal(p,p) parameter, including decimal(3,3) and decimal(2,2).

PR #4443 removed the SqlDecimal -> decimal -> SqlDecimal round-trip to support large decimal values. That round-trip also recomputed precision: increasing the scale of scale-zero zero retains an unnecessary integer digit in SqlDecimal.AdjustScale metadata.

Following review, handle zero in the shared TDSExecuteRPCAddParameter precision check after scale adjustment, covering both CLR decimal and SqlDecimal inputs. Zero fits any valid decimal precision/scale even when its precision metadata is larger. Compare magnitudes to recognize negative zero, retain the existing precision validation for nonzero values, and preserve the large-decimal support from #4443 without restoring a CLR decimal round-trip. This also covers the pre-existing rejection of SqlDecimal zero with excess precision metadata.

No public API changes.

Suggested release note: Fixed an ArgumentException when sending zero-valued decimal parameters whose precision equals their scale.

Issues

Fixes #4715

Regression introduced by 45f4759 (#4443). Preserves support added for #1655.

Backport after merge: release/7.1, targeting 7.1.1. The Hotfix 7.1.1 label schedules the repository's automatic cherry-pick PR workflow after this main-branch PR merges. This PR retains milestone 8.0.0-preview1 to match its target branch.

Testing

• Added RPC-level unit coverage for CLR and SQL positive/negative zero, input scales 0-28, parameter scales 1-38, and both rounding modes. Added excess SQL precision, values rounded/truncated to zero, nonzero precision/rounding, and decimal.MinValue/MaxValue guards. Four SqlDecimal zero cases failed before moving the fix to shared validation.

• Added SQL insertion coverage for decimal(p,p), with p = 1, 2, 3, 28, 29, and 38. Inputs explicitly include 0m, 0.000m, their SqlDecimal equivalents, signed zero, and SQL zero with excess precision. Following review, the scale matrix runs synchronously, with one representative decimal(3,3) async round-trip. Retained sync/async insufficient-precision rejection for both input types and large-decimal round-trip coverage.

• Passed all 18 selected parser unit cases on both .NET 8 and .NET 9.

• Passed all 11 selected integration cases after the review changes on .NET 8 against an isolated SQL Server 2022 container, with no skipped cases.

• Used installed SDK 10.0.102 because the repository-pinned SDK 10.0.401 is unavailable. Integration builds used GenerateDocumentationFile=false to avoid the unrelated nested SDK invocation for XML documentation trimming.

• SQL Server 2025 integration could not run because the local image segfaulted during startup. Windows/.NET Framework, Always Encrypted, and the original macOS/EF Core sample were not run.

• Tests added or updated

• Public API changes documented (not applicable; no API changes)

• Verified against reduced customer repro at the driver serialization layer and direct SQL inserts

• Ensure no breaking changes introduced: existing nonzero validation and large-decimal support retained

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused fix preserves existing behavior and is supported by thorough unit and integration coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes decimal parameter serialization so rescaled CLR zero values fit decimal(p,p) while preserving large-decimal support.

Changes:

• Normalizes rescaled zero precision using SqlDecimal.ConvertToPrecScale.
• Adds comprehensive unit and sync/async integration coverage.
• Documents zero-valued decimal(3,3) parameters.

File	Description
TdsParser.cs	Corrects precision metadata for rescaled CLR zero.
TdsParserDecimalTests.cs	Tests zero, nonzero, rounding, and large values.
ParametersTest.cs	Adds database-level sync/async regression coverage.
SqlParameter.xml	Documents zero with equal precision and scale.
SqlParameter_Precision.cs	Adds the referenced zero-parameter sample.

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[Copilot]

Copilot review overview

🟢 Approval recommended

The focused fix preserves existing behavior and is backed by thorough regression coverage.

Review effort: Balanced
Findings: None

[edwardneal]

Thanks for this, and apologies for the regression. Just one comment about handling the SqlDecimal path - I'd been thinking about handling the 0M case in the check in TDSExecuteRPCAddParameter (line ~10436), after the values have been converted to their final value.

It might also be worth seeing if 0 and 0.000 behave differently in test cases (since one decimal will supply a scale and one won't.)

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused fix preserves nonzero validation and is supported by thorough boundary, regression, and integration tests.

Review effort: Balanced
Findings: None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.11%. Comparing base (671d010) to head (39242a4).

❗ There is a different number of reports uploaded between BASE (671d010) and HEAD (39242a4). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (671d010)	HEAD (39242a4)
CI-SqlClient	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4721      +/-   ##
==========================================
- Coverage   71.96%   64.11%   -7.85%     
==========================================
  Files         291      285       -6     
  Lines       45110    68082   +22972     
==========================================
+ Hits        32462    43654   +11192     
- Misses      12648    24428   +11780     

Flag	Coverage Δ
CI-SqlClient	?
PR-SqlClient-Project	64.11% <100.00%> (?)

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[mdaigle]

Looks good to me. Would be nice to factor out the logic into something that's more easily unit-testable, but I won't block on it.