Resolution errors (ResolveError class in Resolve.java) provide a method (getDiagnostic) to obtain a diagnostic describing the error. This method is very flexible, and allows for creating both a toplevel error diagnostic and a nested fragment diagnostic. The correct behavior depends on the fact that compiler.properties will define "overloaded" keys like:
```
compiler.err.prob.found.req
```
and
```
compiler.misc.prob.found.req
```
This programmatic behavior is hard to capture with the more inflexible diagnostic framework which allows creation of diagnostic keys by using static factories in a generated class, as a way to minimize errors when passing wrong type/number of diagnostic parameters.

For this reason, many instances of diagnostic creation in Resolve are still not using the more robust diagnostic key factories.