[Laurianti]

Contributes to #123137

The [OptionsValidator] source generator replaces [Range] with a synthesized __SourceGen__RangeAttribute. Its FormatErrorMessage always used the built-in message, so ErrorMessage, ErrorMessageResourceName and ErrorMessageResourceType were ignored.

[Range(-20, 55, ErrorMessage = "Temperature must be between -20 and 55.")]
public int Temperature { get; set; }

Before: Temperature: The field MyOptions.Temperature must be between -20 and 55.
After: Temperature: Temperature must be between -20 and 55.

The generated attribute now uses the built-in message only when none of those properties is set. Otherwise it uses ErrorMessageString, like RangeAttribute. The other synthesized attributes (MaxLength, MinLength, Length, Compare) already do this.

The nested member name reported in the issue (SubWeather.Name reported as Name) is not part of this change.

The new TestGeneratedRangeAttributeUsesErrorMessage covers a literal message, a format string, a resource message and the default message. The emitter baselines are updated.

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🟢 Approval recommended

The narrow fix preserves default behavior, includes focused regression coverage, and has no identified blocking issues.

0 open findings

What changed in this PR

Fixes generated Options validators so [Range] honors custom and resource-based error messages while preserving default messages. Nested member naming remains out of scope.

Changes:

• Uses inherited message resolution when customization is configured.
• Adds regression coverage for literal, formatted, resource, and default messages.
• Updates generated-code baselines across target frameworks and language versions.

Builds and tests were not run during this review.

Paths below are relative to src/libraries/Microsoft.Extensions.Options/.

File	Description
tests/​SourceGenerationTests/​Baselines/​NetFX/​Validators.g.cs	Updates .NET Framework baseline.
tests/​SourceGenerationTests/​Baselines/​NetCoreApp/​Validators.g.cs	Updates .NET baseline.
tests/​SourceGeneration.Unit.Tests/​OptionsRuntimeTests.cs	Adds message-customization regression coverage.
tests/​SourceGeneration.Unit.Tests/​Baselines/​OptionsExtendingSystemClassTest.netfx.g.cs	Updates inheritance-test baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​OptionsExtendingSystemClassTest.netcore.g.cs	Updates inheritance-test baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​GeneratedAttributesTest.netfx.lang11.g.cs	Updates C# 11 Framework baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​GeneratedAttributesTest.netfx.lang10.g.cs	Updates C# 10 Framework baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​GeneratedAttributesTest.netcore.lang11.g.cs	Updates C# 11 .NET baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​GeneratedAttributesTest.netcore.lang10.g.cs	Updates C# 10 .NET baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​EmitterWithCustomValidator.netfx.g.cs	Updates custom-validator Framework baseline.
tests/​SourceGeneration.Unit.Tests/​Baselines/​EmitterWithCustomValidator.netcore.g.cs	Updates custom-validator .NET baseline.
gen/​Emitter.cs	Honors configured Range error messages.

🧠 Review effort: Balanced