Macro reform

[glaebhoerl]

At some point, possibly after 1.0, we may want to reform the macro system.

Wishlist items which come up frequently include:

• Having macros be namespaced and scoped under modules the same way as other items are, e.g. one could write std::io::println!("hello world").
• Full hygiene for all items mentioned in macro bodies. (Currently one must write the fully qualified path for items in macros.)
• The ability for macros to refer to private items visible at their definition site, allowing them to be a tool for abstraction, not just convenience.

(The latter two might potentially be accomplished by having all name resolution in macro_rules! bodies happen at the definition site. This article may also be of interest.)

[brendanzab]

Having macros be namespaced and scoped under modules the same way as other items are

I have spoken to @jbclements about this before, and he believes that this is possible. Not sure the specifics though.

[kmcallister]

I wrote up some of my reform ideas, focusing on things we could plausibly do before 1.0. I'm turning this into a proper RFC.

[glaebhoerl]

Closing in favor of #440.