Hi, all.

There is design discussion which is deferred blocker of 3.7.
https://bugs.python.org/issue32911

## Background

An year ago, I moved docstring in AST from statements list to field of
module, class and functions.
https://bugs.python.org/issue29463

Without this change, AST-level constant folding was complicated because
"foo" can be docstring but "fo" + "o" can't be docstring.

This simplified some other edge cases.  For example, future import must
be on top of the module, but docstring can be before it.
Docstring is very special than other expressions/statement.

Of course, this change was backward incompatible.
Tools reading/writing docstring via AST will be broken by this change.
For example, it broke PyFlakes, and PyFlakes solved it already.

https://github.com/PyCQA/pyflakes/pull/273

Since AST doesn't guarantee backward compatibility, we can change
AST if it's reasonable.

Last week, Mark Shannon reported issue about this backward incompatibility.
As he said, this change losted lineno and column of docstring from AST.

https://bugs.python.org/issue32911#msg312567


## Design discussion

And as he said, there are three options:

https://bugs.python.org/issue32911#msg312625

> It seems to be that there are three reasonable choices:
> 1. Revert to 3.6 behaviour, with the addition of `docstring` attribute.
> 2. Change the docstring attribute to an AST node, possibly by modifying the grammar.
> 3. Do nothing.