Avoid code generation if compiler is in error state

One of the things discovered with usage of our proxy generator was that when working in the code and adding things like another property on a class/record. While typing we could see the generator running and spitting out files as we type. For instance, lets say we have the following:

public record DebitAccount(AccountId Id, AccountName Name, PersonId Owner, double Balance);

If I were to now after a build start typing for a fifth property in this, it would start spitting out things. First a file without any name, then as I typed the type I would get a file for each letter I added - depending on how fast I typed. So if this was a string type, I could be seeing s.ts, st.ts, str.ts and so on.

Turns out this is by design. One of the optimizations done for the dotnet build command is that it keeps the compiler process around. It starts a build-server that will handle incremental builds as things is happening and therefor be prepared for when we actually do a dotnet build and be as fast as it can be.

When doing proxy generation, this is obviously less than optimal. To avoid this, we added a check if there are any diagnostics errors from the compiler - if so, do not generate anything.

In our source generator we added a line at the top to avoid this:

public void Execute(GeneratorExecutionContext context)
{
    if (context.Compilation.GetDiagnostics().Any(_ => _.Severity == DiagnosticSeverity.Error)) return;
}