Migration aids

The WM3xxx rules. They ship off, and you turn them on while you convert a codebase to the library.

These two rules ship off. They report on code that has not adopted the library yet, so in most codebases they fire everywhere. Turn them on while you convert, then turn them off again.

ID	What it reports
WM3001	A member that returns a nullable type, where Option<T> would make the absent case impossible to ignore
WM3002	A throw, where returning Result<TOk, Error> would state the failure in the signature

Enable one in your .editorconfig:

[*.cs]
dotnet_diagnostic.WM3001.severity = suggestion
dotnet_diagnostic.WM3002.severity = suggestion

WM3002 ignores the throws a Result would not improve: ArgumentException and its subtypes, NotImplementedException, NotSupportedException, ObjectDisposedException, a bare throw; rethrow, and any throw inside a lambda you pass to Option.Try or Result.Try.

WM3001

A nullable return leaves the absent case easy to ignore. Option<T> makes the caller acknowledge it. Off by default, because in a codebase that has not adopted the library this fires on nearly every member.

-User? FindUser(int id);
+Option<User> FindUser(int id);

WM2012 is the narrower, on-by-default version, for a type that already uses Option elsewhere.

WM3002

A throw states a failure nowhere in the signature. Returning Result<TOk, Error> puts it there, where a caller cannot miss it. Off by default, because it fires on every throw in a codebase that has not adopted Result.

-if (!found) throw new InvalidOperationException("no such user");
+if (!found) return new Error("NoSuchUser", "no such user");

It skips the throws listed above, which a Result would not improve. WM2003 is the on-by-default version, for a member that already returns Result.