bug#57397: cl-letf blindly macroexpands places

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>> > Maybe it's enough to expand only symbol macros?
>> Yes, that should still cover the original need in bug#26073 without
>> breaking your use case.
> Was it necessary to really expand symbol macros to fix that bug, or is
> the purpose only to handle the following `symbolp' test correctly?

No the problem shows up in the `gv-letplace` that follows immediately,
so by the time we get to the `symbolp` test it's too late.
But I suspect that the better fix is to skip the macroexpand call here
and to change `gv-get` so as to do a `macroexpand-1` call even if its
arg is a `symbolp`.

>> But regardless of this, we should probably turn `gv-synthetic-place`
>> into a function so it's more robust.
> Why is it a macro?

Beats me.
I tried to ask the original author but he was not available for comments.

> Seems to work quite as well (using the same body and
> gv-spec) when defined as a function.

The only downside is that the code is less efficient (the getter has to
construct the closure of the setter, then call `gv-synthetic-place`
which then just throws it away) but that should be easy to fix with
a compiler macro.


        Stefan