crate shorthand visibility modifier

With regrets, this breaks rustfmt and rls.

This is in the matter of #45388.

Author: zackmdavis

src/doc/unstable-book/src/language-features/crate-visibility-modifier.md

@@ -0,0 +1,20 @@
+# `crate_visibility_modifier`
+
+The tracking issue for this feature is: [#45388]
+
+[#45388]: https://github.com/rust-lang/rust/issues/45388
+
+-----
+
+The `crate_visibility_modifier` feature allows the `crate` keyword to be used
+as a visibility modifier synonymous to `pub(crate)`, indicating that a type
+(function, _&c._) is to be visible to the entire enclosing crate, but not to
+other crates.
+
+```rust
+#![feature(crate_visibility_modifier)]
+
+crate struct Foo {
+    bar: usize,
+}
+```

src/librustc/hir/lowering.rs

@@ -2666,7 +2666,7 @@ impl<'a> LoweringContext<'a> {
                         -> hir::Visibility {
         match *v {
             Visibility::Public => hir::Public,
-            Visibility::Crate(_) => hir::Visibility::Crate,
+            Visibility::Crate(..) => hir::Visibility::Crate,
             Visibility::Restricted { ref path, id } => {
                 hir::Visibility::Restricted {
                     path: P(self.lower_path(id, path, ParamMode::Explicit, true)),

src/libsyntax/ast.rs

@@ -1787,10 +1787,19 @@ impl PolyTraitRef {
     }
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum CrateSugar {
+    /// Source is `pub(crate)`
+    PubCrate,
+
+    /// Source is (just) `crate`
+    JustCrate,
+}
+
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum Visibility {
     Public,
-    Crate(Span),
+    Crate(Span, CrateSugar),
     Restricted { path: P<Path>, id: NodeId },
     Inherited,
 }

src/libsyntax/feature_gate.rs

@@ -401,6 +401,9 @@ declare_features! (
 
     // Trait object syntax with `dyn` prefix
     (active, dyn_trait, "1.22.0", Some(44662)),
+
+    // `crate` as visibility modifier, synonymous to `pub(crate)`
+    (active, crate_visibility_modifier, "1.23.0", Some(45388)),
 );
 
 declare_features! (
@@ -1582,6 +1585,14 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_impl_item(self, ii);
     }
 
+    fn visit_vis(&mut self, vis: &'a ast::Visibility) {
+        if let ast::Visibility::Crate(span, ast::CrateSugar::JustCrate) = *vis {
+            gate_feature_post!(&self, crate_visibility_modifier, span,
+                               "`crate` visibility modifier is experimental");
+        }
+        visit::walk_vis(self, vis);
+    }
+
     fn visit_generics(&mut self, g: &'a ast::Generics) {
         for t in &g.ty_params {
             if !t.attrs.is_empty() {

src/libsyntax/parse/parser.rs

@@ -36,7 +36,7 @@ use ast::SelfKind;
 use ast::{TraitItem, TraitRef, TraitObjectSyntax};
 use ast::{Ty, TyKind, TypeBinding, TyParam, TyParamBounds};
 use ast::{ViewPath, ViewPathGlob, ViewPathList, ViewPathSimple};
-use ast::{Visibility, WhereClause};
+use ast::{Visibility, WhereClause, CrateSugar};
 use ast::{BinOpKind, UnOp};
 use ast::{RangeEnd, RangeSyntax};
 use {ast, attr};
@@ -5325,6 +5325,10 @@ impl<'a> Parser<'a> {
     pub fn parse_visibility(&mut self, can_take_tuple: bool) -> PResult<'a, Visibility> {
         maybe_whole!(self, NtVis, |x| x);
 
+        if self.eat_keyword(keywords::Crate) {
+            return Ok(Visibility::Crate(self.prev_span, CrateSugar::JustCrate));
+        }
+
         if !self.eat_keyword(keywords::Pub) {
             return Ok(Visibility::Inherited)
         }
@@ -5338,7 +5342,7 @@ impl<'a> Parser<'a> {
                 // `pub(crate)`
                 self.bump(); // `(`
                 self.bump(); // `crate`
-                let vis = Visibility::Crate(self.prev_span);
+                let vis = Visibility::Crate(self.prev_span, CrateSugar::PubCrate);
                 self.expect(&token::CloseDelim(token::Paren))?; // `)`
                 return Ok(vis)
             } else if self.look_ahead(1, |t| t.is_keyword(keywords::In)) {

src/libsyntax/print/pprust.rs

@@ -1440,7 +1440,10 @@ impl<'a> State<'a> {
     pub fn print_visibility(&mut self, vis: &ast::Visibility) -> io::Result<()> {
         match *vis {
             ast::Visibility::Public => self.word_nbsp("pub"),
-            ast::Visibility::Crate(_) => self.word_nbsp("pub(crate)"),
+            ast::Visibility::Crate(_, sugar) => match sugar {
+                ast::CrateSugar::PubCrate => self.word_nbsp("pub(crate)"),
+                ast::CrateSugar::JustCrate => self.word_nbsp("crate")
+            }
             ast::Visibility::Restricted { ref path, .. } => {
                 let path = to_string(|s| s.print_path(path, false, 0, true));
                 if path == "self" || path == "super" {

src/test/compile-fail/feature-gate-crate_visibility_modifier.rs

@@ -0,0 +1,18 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+crate struct Bender { //~ ERROR `crate` visibility modifier is experimental
+    earth: bool,
+    fire: bool,
+    air: bool,
+    water: bool,
+}
+
+fn main() {}

src/test/compile-fail/privacy/restricted/auxiliary/pub_restricted.rs

@@ -8,14 +8,19 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(crate_visibility_modifier)]
+
 pub(crate) struct Crate;
+
 #[derive(Default)]
 pub struct Universe {
     pub x: i32,
-    pub(crate) y: i32
+    pub(crate) y: i32,
+    crate z: i32,
 }
 
 impl Universe {
     pub fn f(&self) {}
     pub(crate) fn g(&self) {}
+    crate fn h(&self) {}
 }

src/test/compile-fail/privacy/restricted/private-in-public.rs

@@ -8,12 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(crate_visibility_modifier)]
+
 mod foo {
     struct Priv;
     mod bar {
         use foo::Priv;
         pub(super) fn f(_: Priv) {}
         pub(crate) fn g(_: Priv) {} //~ ERROR E0446
+        crate fn h(_: Priv) {} //~ ERROR E0446
     }
 }
 

src/test/compile-fail/privacy/restricted/test.rs

@@ -50,8 +50,10 @@ fn main() {
     let u = Universe::default();
     let _ = u.x;
     let _ = u.y; //~ ERROR private
+    let _ = u.z; //~ ERROR private
     u.f();
     u.g(); //~ ERROR private
+    u.h(); //~ ERROR private
 }
 
 mod pathological {