I understand what's happening, I just find this extremely confusing. Can byte-compilation not notice that there is a `defvar' form and thus count the variable as special also during compilation?
> Try this:
This cannot be done in the real cases where things break, because they (`iter-defun', for example) _need_ to know if the variable is special at the time macro gets expanded (they call internal helper functions that call `special-variable-p' in turn).
The only workaround I'm aware of is putting `defvar' into an `eval-and-compile' form (or into a different file, as `require' implicitly does that). I consider this a workaround rather than a proper solution since it is very confusing and not even apparent to many users (pretty much to most of those who never stumbled into this issue). Also, resulting errors are not self-explanatory and can be anything, including incomprehensible and seemingly unrelated failures at runtime . Additionally, you need to know if said variable is going to be used in a macro that uses `special-variable-p' in its expansion code; in particular, you need to know the list of such macros (I currently know two related real-word examples: `iter-defun' and friends from the standard feature `generator' and `iter2-defun' and friends from library `iter2'). Normally, you don't even think about putting `defvar' into an `eval-and-compile'.
As mentioned, I think that byte-compilation should be improved to mark variables as special during compilation time too, so that there is no need in `eval-and-compile'. I.e. even if this is not considered a bug, it should count as a feature request.
Paul