Re: Strange change in backquote expansion

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

>> Since 19.29 was 12 years ago, I think it is time to delete the
>> documentation of that compatibility feature.  Does anyone object?

>     I believe the old syntax is still used in some of the bundled
>     packages, not to mention the unbundled ones.

> Can you arrange to issue a warning when reading code that uses the old
> syntax?  There could be a flag to control the warning, and for the moment
> we could make only the byte compiler turn on the flag.  That would make
> it convenient if the warnings come thru the compiler warning mechanism.

How 'bout the following:

- add a new variable no-old-style-backquotes, with 2 values:
  t   = treat all backquotes and commas as new style
  nil = behave like now (i.e. try to tell which is which)

- add a new variable new-old-style-backquotes.
  When no-old-style-backquotes is t and we encounter an old-style backquote,
  remember the fact in this variable (could be just a boolean flag or a list
  of the affected sexps).
  I.e. this keeps track of the backquotes that used to be treated as
  old-style but have been instead treated as new-style.

Then default no-old-style-backquotes to nil, but bind it to t in the
byte-compiler (and at the end of byte-compilation of a file, check
new-old-style-backquotes to see if there's been something fishy and warn
about it if so).


        Stefan