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, 4 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 89f318d0945..0d38411ac93 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -82,7 +82,7 @@ const KNOWN_FEATURES: &'static [(&'static str, &'static str, Option<u32>, Status
     ("advanced_slice_patterns", "1.0.0", Some(23121), Active),
     ("tuple_indexing", "1.0.0", None, Accepted),
     ("associated_types", "1.0.0", None, Accepted),
-    ("visible_private_types", "1.0.0", Some(29627), Active),
+    ("visible_private_types", "1.0.0", None, Removed),
     ("slicing_syntax", "1.0.0", None, Accepted),
     ("box_syntax", "1.0.0", Some(27779), Active),
     ("placement_in_syntax", "1.0.0", Some(27779), Active),
@@ -514,7 +514,6 @@ pub enum AttributeGate {
 pub struct Features {
     pub unboxed_closures: bool,
     pub rustc_diagnostic_macros: bool,
-    pub visible_private_types: bool,
     pub allow_quote: bool,
     pub allow_asm: bool,
     pub allow_log_syntax: bool,
@@ -551,7 +550,6 @@ impl Features {
         Features {
             unboxed_closures: false,
             rustc_diagnostic_macros: false,
-            visible_private_types: false,
             allow_quote: false,
             allow_asm: false,
             allow_log_syntax: false,
@@ -1130,7 +1128,6 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &Handler,
     Features {
         unboxed_closures: cx.has_feature("unboxed_closures"),
         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
-        visible_private_types: cx.has_feature("visible_private_types"),
         allow_quote: cx.has_feature("quote"),
         allow_asm: cx.has_feature("asm"),
         allow_log_syntax: cx.has_feature("log_syntax"),