[Proposal]: Breaking change warnings

[MadsTorgersen]

Breaking change warnings

• Specification: https://github.com/dotnet/csharplang/blob/main/proposals/breaking-change-warnings.md
• Discussion: [Proposal]: Breaking change warnings #8864

Summary

Allow very limited breaking changes in C# when this enables significantly simpler feature designs that are easier to learn, understand and use.

Retroactively add warnings in previous language versions to help identify and fix user code that would be vulnerable to such breaks upon a language version upgrade.

Design meetings

https://github.com/dotnet/csharplang/blob/main/meetings/2023/LDM-2023-10-16.md#breaking-change-warnings
https://github.com/dotnet/csharplang/blob/main/meetings/2024/LDM-2024-02-07.md#breaking-change-warnings
https://github.com/dotnet/csharplang/blob/main/meetings/2024/LDM-2024-03-04.md#breaking-changes-making-field-and-value-contextual-keywords