[release/11.0] Validate unsupported SQL Server JSON index options

[Copilot]

Fixes #39065

Description
SQL Server JSON indexes cannot express several options supported by ordinary indexes. EF Core generated CREATE JSON INDEX while silently dropping options such as uniqueness and descending order, or emitted clauses that SQL Server does not support. This change validates JSON index configuration and reports an error identifying the index and unsupported option. It continues to allow supported options and harmless explicit defaults, including fill factor, non-clustered, no include properties, offline creation, and disabled tempdb sorting.

Customer impact
Applications could configure a JSON-member index as unique but receive a non-unique database index, allowing duplicate values despite the model constraint. Other unsupported options could produce SQL that fails when a migration is applied. There was no warning that the intended constraint had been discarded.

builder.HasIndex(e => e.Details.Slug)
    .IsUnique();

How found
User reported on EF Core 11.0.0-rc1 .

Regression
No, SQL Server JSON index support was introduced in EF Core 11.

Testing
Tests added.

Risk
Low. SQL generation is unchanged. The validation only rejects options that SQL Server JSON indexes cannot express.

[Copilot]

Copilot review overview

🟡 Changes recommended

Validation incorrectly rejects harmless explicit defaults such as nonclustered indexes and empty include lists.

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Review effort: Balanced
Findings: 1

Open (1)

• Reject only clustered indexes and non-empty include lists · New

What changed in this PR

Adds SQL Server model validation to prevent unsupported JSON index options from being silently ignored.

Changes:

• Validates JSON index options during model finalization.
• Adds provider-specific diagnostics.
• Adds supported and unsupported option tests.

File	Description
SqlServerModelValidator.cs	Validates JSON index options.
SqlServerStrings.resx	Adds validation error text.
SqlServerStrings.Designer.cs	Exposes the generated error resource.
SqlServerModelValidatorTest.cs	Tests option validation.

Files not reviewed (1)

• src/EFCore.SqlServer/Properties/SqlServerStrings.Designer.cs: Generated file

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[Copilot]

Copilot review overview

🟢 Approval recommended

The focused validation matches SQL Server JSON-index constraints and has comprehensive unit coverage.

Review effort: Balanced
Findings: None

Resolved since last review (1)

• Reject only clustered indexes and non-empty include lists

Files not reviewed (1)

• src/EFCore.SqlServer/Properties/SqlServerStrings.Designer.cs: Generated file

[artl93]

Approved. New area. Customer reported.