save-restriction seems to fail in certain circumstances

[telotortium]

When running code that uses save-restriction under ert, in certain circumstances an error is encountered. I don't have it at hand right now, but essentially, save-restriction attempts to restore point-max in the *ert* buffer, not the buffer I created for the test and in which I originally ran save-restriction, and that fails because my buffer is larger than the *ert* buffer.

In general, it seems like internally save-restriction, save-excursion, save-current-buffer are implemented essentially using unwind-protect (example). Basically, it seems like save-current-buffer just saves the current buffer, save-excursion saves instead a marker to the current point in the current buffer (as well as the current window), and save-restriction saves markers to the min and max points in the current buffer. iter2's save-restriction, however, does not restore the current buffer from the markers before calling narrow-to-region, which I believe causes the bug.

In general, it may be a better idea to manually convert these 3 macros to equivalent unwind-protect forms, following the Emacs source code, and then convert those.

[doublep]

I need to see the failing code. If you are using only save-restriction without saving the buffer in the generator function, you implicitly require that the caller doesn't switch the buffer when control is yielded back to it. If the caller (or ERT in "its name") does, it is expected that the generator function will fail as unprepared for that.

In general, it may be a better idea to manually convert these 3 macros to equivalent unwind-protect forms, following the Emacs source code, and then convert those.

I'm pretty sure this won't work. iter2 has special support for several save-* special forms and macros, because they involve storing of additional global state (current buffer, match data, etc.). This additional global state is never handled in processing of any other special forms and so wouldn't be handled when processing equivalent code.

As a hint, these forms are not handled by Emacs built-in generator at all, and for a reason: this is not trivial.