librustc: Make unqualified identifier searches terminate at the nearest ...

[pcwalton]

...module scope

r? @catamorphism

[Dretch]

Does this mean that every single module needs to include use core::prelude::*; in its imports?

[catamorphism]

r+ but a commit message explaining the change -- and the reasons for it -- in a little more detail, for posterity, would be nice. Also, do either the reference manual or the tutorial need to be updated as a result of the new name resolution rules?

[pcwalton]

@Dretch No, it's only a pain for us in rustc. User code doesn't have to write that import.

The reason why rustc bears this pain is that, due to obscure reasons related to the way core injection works and the multistage bootstrapping process, the build will break due to multiple versions of libcore right after we bump the version of core if we let rustc include core automatically.

[catamorphism]

I think my comment may have been off-base, then, but a more descriptive commit message would still help.

[catamorphism]

Merged in 57c5999