Source Generator for project itself

[aka-nse]

In today's C#, metaprogramming using Source Generators is widely utilized.
There are various use cases for Source Generators, including those intended for broad use as a library by end users, as well as those meant to be used solely within specific projects.

Currently, even for the latter use case, Roslyn requires the creation of a dedicated project for the generator and appropriate configuration on the project side utilizing it.

To alleviate this complexity, could we not allow for the unified management of generator source code within a single project?

• Differentiate between build asset source code (.cs) and generator source code (e.g. .csgen) using file extensions.

• Apply different target frameworks to build assets and generators.

• Generators created from *.csgen are only effective within the same project's *.cs or files specified as AdditionalFiles.

• Generator binaries are updated after the build. They remain effective in *.cs files until the next rebuild of *.csgen.

• It might be more convenient if nameof expressions in *.csgen could reference namespaces, types, and members defined in *.cs.
  (I think these would be achieved by simply embedding them as string constants; it is probably not able to enable typeof.)

Thank you.