You can absolutely do global knowledge in proc macros via the filesystem and commit their output to version control: https://github.com/trevyn/turbosql
You can introduce side effects to a proc macro (but please avoid if at all possible), but you cannot control the order in which proc macros are run. If you need to reason about the global schema while generating code, that won’t work.
In this case, for example, it looks like the generated code needs global knowledge of related ORM types in the data model, and that just isn't supported by proc-macros. You could push some of that into the trait system, but it would be complex to the point where a custom DSL starts to look appealing.
Proc-macros also cannot be run "offline", i.e. you can't commit their output to version control. They run every time the compiler runs, slowing down `cargo check` and rust-analyzer.