Auto merge of #29973 - petrochenkov:privinpub, r=nikomatsakis

Some notes:
This patch enforces the rules from [RFC 136](https://github.com/rust-lang/rfcs/blob/master/text/0136-no-privates-in-public.md) and makes "private in public" a module-level concept and not crate-level. Only `pub` annotations are used by the new algorithm, crate-level exported node set produced by `EmbargoVisitor` is not used. The error messages are tweaked accordingly and don't use the word "exported" to avoid confusing people (https://github.com/rust-lang/rust/issues/29668).

The old algorithm tried to be extra smart with impls, but it mostly led to unpredictable behavior and bugs like https://github.com/rust-lang/rust/issues/28325.
The new algorithm tries to be as simple as possible - an impl is considered public iff its type is public and its trait is public (if presents).
A type or trait is considered public if all its components are public, [complications](https://internals.rust-lang.org/t/limits-of-type-inference-smartness/2919) with private types leaking to other crates/modules through trait impls and type inference are deliberately ignored so far.

The new algorithm is not recursive and uses the nice new facility `Crate::visit_all_items`!

Obsolete pre-1.0 feature `visible_private_types` is removed.

This is a [breaking-change].
The two main vectors of breakage are type aliases (https://github.com/rust-lang/rust/issues/28450) and impls (https://github.com/rust-lang/rust/issues/28325).
I need some statistics from a crater run (cc @alexcrichton) to decide on the breakage mitigation strategy.
UPDATE: All the new errors are reported as warnings controlled by a lint `private_in_public` and lint group `future_incompatible`, but the intent is to make them hard errors eventually.

Closes https://github.com/rust-lang/rust/issues/28325
Closes https://github.com/rust-lang/rust/issues/28450
Closes https://github.com/rust-lang/rust/issues/29524
Closes https://github.com/rust-lang/rust/issues/29627
Closes https://github.com/rust-lang/rust/issues/29668
Closes https://github.com/rust-lang/rust/issues/30055

r? @nikomatsakis

1 files changed, 1 insertions, 1 deletions

diff --git a/src/test/debuginfo/type-names.rs b/src/test/debuginfo/type-names.rs
index 3db3e9d311d..a74369ed3c3 100644
--- a/src/test/debuginfo/type-names.rs
+++ b/src/test/debuginfo/type-names.rs
@@ -182,7 +182,7 @@ use self::Enum1::{Variant1, Variant2};
 use std::marker::PhantomData;
 use std::ptr;
 
-struct Struct1;
+pub struct Struct1;
 struct GenericStruct<T1, T2>(PhantomData<(T1,T2)>);
 
 enum Enum1 {