Support DefaultValueAttribute in AIFunctionFactory parameter handling

[Copilot]

• Understand the issue: Parameters with [DefaultValue(null)] are treated as required instead of optional
• Identify the root cause: ParameterInfo.IsOptional and ParameterInfo.HasDefaultValue are false for [DefaultValue] attributes
• Locate code changes needed
• Implement helper methods to check for DefaultValueAttribute
• Update schema generation to treat DefaultValueAttribute as optional
• Update parameter marshaling to use DefaultValueAttribute values
• Add comprehensive tests including precedence test
• Build and test the changes
• Address PR feedback:
  • Revert .gitignore changes
  • Fix formatting issues in test file
  • Consolidate duplicate helper methods
  • Use longer parameter name in test
  • Unify into single TryGetEffectiveDefaultValue method

Summary

Successfully implemented support for the [DefaultValue] attribute in AIFunctionFactory. Parameters decorated with [DefaultValue] are now treated as optional in the JSON schema and function invocation, matching the behavior of C# default values.

Changes Made:

1. AIJsonUtilities.Schema.Create.cs: Added internal TryGetEffectiveDefaultValue helper method to check for and retrieve default values from both C# defaults and DefaultValueAttribute in a single call
2. AIFunctionFactory.cs: Updated parameter marshaling to use the unified helper method from AIJsonUtilities
3. Tests: Added comprehensive tests covering null, non-null, and int default values, plus precedence when both are present

Security Considerations:

• No security vulnerabilities introduced
• Default values from attributes are treated the same as C# defaults
• All validation remains in place

Original prompt

With AIFunctionFactory, when a parameter is optional (e.g. string? s = null), it gets listed in the schema as being non-required. However, when that default value is instead supplied with [DefaultValue(null)] (e.g. [DefaultValue(null)] string? s), the DefaultValue attribute isn't currently being factored in. Please fix that, such that DefaultValue is treated the same as if a default value were supplied using the C# syntax.

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Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR adds support for the [DefaultValue] attribute in AIFunctionFactory, ensuring parameters decorated with this attribute are treated as optional in the same way as parameters with C# default value syntax.

Key Changes:

• Added helper methods to detect and retrieve default values from both [DefaultValue] attribute and C# default syntax
• Updated schema generation to correctly mark parameters with [DefaultValue] as optional
• Updated parameter marshaling to use default values from [DefaultValue] attribute

Reviewed Changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 3 comments.

File	Description
AIJsonUtilities.Schema.Create.cs	Added HasEffectiveDefaultValue() and GetEffectiveDefaultValue() helpers to check for both C# defaults and [DefaultValue] attribute; updated schema generation logic to use these helpers
AIFunctionFactory.cs	Added duplicate helper methods and updated parameter marshaling to respect [DefaultValue] attribute
AIFunctionFactoryTest.cs	Added comprehensive test coverage for [DefaultValue] attribute functionality including null values, non-null values, and precedence scenarios

[stephentoub]

@copilot, please fix the formatting diagnostics:

Build FAILED.

/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(69,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(75,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(78,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(81,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(87,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(90,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(96,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(99,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(105,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net9.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(69,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(75,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(78,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(81,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(87,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(90,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(96,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(99,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Functions/AIFunctionFactoryTest.cs(105,1): error IDE0055: Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055) [/mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.AI.Tests/Microsoft.Extensions.AI.Tests.csproj::TargetFramework=net8.0]
    0 Warning(s)
    18 Error(s)

[Copilot]

@copilot, please fix the formatting diagnostics:

Build FAILED.

...

Fixed in c79b280. Removed extra blank lines that were causing IDE0055 formatting errors.