[erlang-patches] add compiler checked atoms

[Richard Carlsson]

Sorry, pressed send too soon in the last attempt. Here is the code:

   git fetch git@REDACTED:richcarl/otp.git warn-unknown-atom

Here is a suggested patch to the compiler, that I'm throwing out there 
as a request for comments. In any large code base, it can be hard to 
maintain atom hygiene - you may have hidden errors due to misspelled 
atoms, people may be adding atoms without much thought, and it can be 
hard to track which atoms are being used where and for what (e.g., atoms 
used for options, error indicators, message tags, callback module and 
function names, etc. This allows you to declare your atoms like so:

   -atoms([foo, bar]).

You can have any number of such declarations, and an atom may occur 
multiple times and/or in different declarations - it's the union of 
known atoms that matters. Note that this declaration is backwards 
compatible; the current compiler will accept it as a generic attribute 
with no particular meaning.

If you specify the compiler option `warn_unused_atom' when compiling a 
module (you can put `-compile([warn_unused_atom]).' in the module if you 
want to enable the checking in that module only), you will get a warning 
for each atom that has not been explicitly declared. The compiler knows 
about standard atoms such as `ok', `true', `false', `undefined' etc., 
and it does not check function and module names in calls, or record 
names and fields of records, since these are checked in other ways already.

I don't think this addition warrants an EEP, since it doesn't change the 
language as such; it only adds a backwards compatible feature to the 
compiler. However, I'd like to get some initial feedback before I bother 
to update the documentation and submit it as a full patch.

git@REDACTED:richcarl/otp.git

    /Richard