Reviewing generated codes

Commit your error codes as a list, and make a divergence fail the build rather than a rename change a wire contract silently.

Reviewing your codes as a list

An error code is a wire contract, and the thing that makes one hard to hold onto is that a rename changes it silently. You can make the whole set reviewable by committing it.

Add an ErrorCodes.txt to the project and list it as an AdditionalFiles item:

<ItemGroup>
    <AdditionalFiles Include="ErrorCodes.txt"/>
</ItemGroup>

That is the whole opt-in — the same shape as PublicAPI.Shipped.txt for the public API analyzers. A project without the file never sees either rule.

The file is one code per line. Blank lines are ignored and a line starting with # is a comment:

# Every error code this project publishes. Reviewed on change.
order.already-shipped
order.not-found

Two rules then keep it honest:

ID	What it reports
WM2019	An enum member generates a code the file does not list
WM2020	The file lists a code no catalog generates

WM2019 has a code fix, Update ErrorCodes.txt, which rewrites the whole file from the compilation: it adds every missing code and removes every stale entry in one pass, sorted, keeping your leading comment block. So a rename shows up as one removed line and one added line, and you read it in the diff before you commit it.

WM2020 has no code fix of its own. It is reported against ErrorCodes.txt rather than against any of your source, and Roslyn does not offer fixes for a diagnostic reported at the end of a compilation. In practice this does not come up: the WM2019 fix removes stale entries too. A project whose only divergence is a stale entry deletes the line the message names.

Making a divergence fail the build

Both rules ship as suggestions, so by default they show in the IDE and not in CI. If you have committed the file you probably want the opposite. WM2019 responds to an ordinary .editorconfig:

[*.cs]
dotnet_diagnostic.WM2019.severity = warning

WM2020 does not. It is reported against ErrorCodes.txt, which has no syntax tree, and Roslyn resolves dotnet_diagnostic severities per syntax tree — so a path-matched section is never consulted for it, including [*]. Raising it takes a global analyzer config:

is_global = true
dotnet_diagnostic.WM2019.severity = warning
dotnet_diagnostic.WM2020.severity = warning

Put that in a .globalconfig next to the project. A global config covers both rules, so it is the simpler thing to write even though only one of them needs it.

Renaming is a breaking change

The code is built from two names: the enum's and the member's. Rename either (or edit the format) and every consumer reading the code sees a different string, with nothing in the compiler to tell you.

[ErrorCodeCatalog]
public enum OrderErrorCode   // rename this -> every code changes
{
    NotFound,                // rename this -> "OrderErrorCode.NotFound" changes
}

This is not new — ErrorCode.FromEnum worked the same way, and ErrorCode's own guidance is that a code should not change between occurrences of the same error. Treat an attributed enum as a published contract, the way you would treat a URL.