[Proposal]: Interpolated string handler method names

[333fred]

Interpolated string handler method names

• Specification: https://github.com/dotnet/csharplang/blob/main/proposals/interpolated-string-handler-argument-value.md
• Discussion: Interpolated string handler method names #9047

Summary

In order to solve a pain point in the creation of handler types and make them more useful in logging scenarios, we add support for interpolated string handlers to receive a new piece of information, a custom value supplied at the call site.

public void LogDebug(
    this ILogger logger,
    [InterpolatedStringHandlerArgument(nameof(logger))]
    [InterpolatedStringHandlerArgumentValue(LogLevel.Debug)]
    LogInterpolatedStringHandler message);

Design meetings

• https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-01-15.md#interpolated-string-handler-method-names
• https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-02-24.md#interpolated-string-handler-method-names
• https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-04-07.md#interpolated-string-handler-argument-values