RelationalDiagnostics: Naming inconsistencies

[NickCraver]

I'm working on a DiagnosticListener approach in #7939 and noticed some inconsistencies in RelationalDiagnostics.cs:

1. ConnectionError is incorrect, nameof(ConnectionClosed) (repeated)should benameof(ConnectionError)`. I've submitted PR Fix diagnostic name for RelationalDiagnostics.ConnectionError #8000 to correct this.

public const string ConnectionClosed = NamePrefix + nameof(ConnectionClosed);
public const string ConnectionError = NamePrefix + nameof(ConnectionClosed);

2. "TransactionRolledBack" isn't title cased:

public const string TransactionRolledback = NamePrefix + nameof(TransactionRolledback);

^ this should have a capital B to be consistent with all other events. in the class, e.g.

public const string TransactionRolledBack = NamePrefix + nameof(TransactionRolledBack);

1 is an obvious bug (unless I'm nuts) and causing active harm re-firing the closed event on errors, not just closes. While there's a workaround of using the exception arg on the close listener and seeing if it's null, this is both a) not ensure to be reliable, and b) just plain wrong.

2 is minor, but a breaking change to listeners all the same. At the same time, I can't find anyone even using this yet (or someone would have noticed these things?) - should we fix it properly now?

See #7939 (comment) for additional concerns I have about the stability of these APIs. Since everyone is (as far as I know) copying these strings because they are internally restricted, there's no scenario fixed by a simple recompile. Issues like this would be better served in the event names were exposed and compilationally reliable.

[ajcvickers]

@NickCraver Thanks for the PR for 1. We would also take a PR for 2, since we can take reasonable breaking changes in the 2.0 release. Would you be willing to send a PR?

[anpete]

I think this has all been taken care of with @ajcvickers rework of this area.