Auto merge of #20179 - eddyb:blind-items, r=alexcrichton

This implements an important part of RFC PR 385 (see #18219).

src/doc/reference.md

@@ -803,8 +803,9 @@ Crates contain [items](#items), each of which may have some number of
 ## Items
 
 ```{.ebnf .gram}
-item : mod_item | fn_item | type_item | struct_item | enum_item
-     | static_item | trait_item | impl_item | extern_block ;
+item : extern_crate_decl | use_decl | mod_item | fn_item | type_item
+     | struct_item | enum_item | static_item | trait_item | impl_item
+     | extern_block ;
 ```
 
 An _item_ is a component of a crate; some module items can be defined in crate
@@ -818,6 +819,8 @@ execution, and may reside in read-only memory.
 
 There are several kinds of item:
 
+* [`extern crate` declarations](#extern-crate-declarations)
+* [`use` declarations](#use-declarations)
 * [modules](#modules)
 * [functions](#functions)
 * [type definitions](#type-definitions)
@@ -854,13 +857,10 @@ no notion of type abstraction: there are no first-class "forall" types.
 
 ```{.ebnf .gram}
 mod_item : "mod" ident ( ';' | '{' mod '}' );
-mod : [ view_item | item ] * ;
+mod : item * ;
 ```
 
-A module is a container for zero or more [view items](#view-items) and zero or
-more [items](#items). The view items manage the visibility of the items defined
-within the module, as well as the visibility of names from outside the module
-when referenced from inside the module.
+A module is a container for zero or more [items](#items).
 
 A _module item_ is a module, surrounded in braces, named, and prefixed with the
 keyword `mod`. A module item introduces a new, named module into the tree of
@@ -918,19 +918,6 @@ mod thread {
 }
 ```
 
-#### View items
-
-```{.ebnf .gram}
-view_item : extern_crate_decl | use_decl ;
-```
-
-A view item manages the namespace of a module. View items do not define new
-items, but rather, simply change other items' visibility. There are two
-kinds of view items:
-
-* [`extern crate` declarations](#extern-crate-declarations)
-* [`use` declarations](#use-declarations)
-
 ##### Extern crate declarations
 
 ```{.ebnf .gram}
@@ -2891,13 +2878,12 @@ Point3d {y: 0, z: 10, .. base};
 ### Block expressions
 
 ```{.ebnf .gram}
-block_expr : '{' [ view_item ] *
-                 [ stmt ';' | item ] *
+block_expr : '{' [ stmt ';' | item ] *
                  [ expr ] '}' ;
 ```
 
 A _block expression_ is similar to a module in terms of the declarations that
-are possible. Each block conceptually introduces a new namespace scope. View
+are possible. Each block conceptually introduces a new namespace scope. Use
 items can bring new names into scopes and declared items are in scope for only
 the block itself.
 

src/librustc/diagnostics.rs

@@ -52,6 +52,7 @@ register_diagnostics! {
     E0140,
     E0152,
     E0153,
+    E0154,
     E0157,
     E0158,
     E0161,

src/librustc/lint/builtin.rs

@@ -1202,17 +1202,17 @@ impl LintPass for UnusedImportBraces {
         lint_array!(UNUSED_IMPORT_BRACES)
     }
 
-    fn check_view_item(&mut self, cx: &Context, view_item: &ast::ViewItem) {
-        match view_item.node {
-            ast::ViewItemUse(ref view_path) => {
+    fn check_item(&mut self, cx: &Context, item: &ast::Item) {
+        match item.node {
+            ast::ItemUse(ref view_path) => {
                 match view_path.node {
-                    ast::ViewPathList(_, ref items, _) => {
+                    ast::ViewPathList(_, ref items) => {
                         if items.len() == 1 {
                             match items[0].node {
                                 ast::PathListIdent {ref name, ..} => {
                                     let m = format!("braces around {} is unnecessary",
                                                     token::get_ident(*name).get());
-                                    cx.span_lint(UNUSED_IMPORT_BRACES, view_item.span,
+                                    cx.span_lint(UNUSED_IMPORT_BRACES, item.span,
                                                  &m[]);
                                 },
                                 _ => ()
@@ -1709,22 +1709,6 @@ impl LintPass for Stability {
         }
     }
 
-    fn check_view_item(&mut self, cx: &Context, item: &ast::ViewItem) {
-        // compiler-generated `extern crate` statements have a dummy span.
-        if item.span == DUMMY_SP { return }
-
-        let id = match item.node {
-            ast::ViewItemExternCrate(_, _, id) => id,
-            ast::ViewItemUse(..) => return,
-        };
-        let cnum = match cx.tcx.sess.cstore.find_extern_mod_stmt_cnum(id) {
-            Some(cnum) => cnum,
-            None => return,
-        };
-        let id = ast::DefId { krate: cnum, node: ast::CRATE_NODE_ID };
-        self.lint(cx, id, item.span);
-    }
-
     fn check_expr(&mut self, cx: &Context, e: &ast::Expr) {
         if self.is_internal(cx, e.span) { return; }
 
@@ -1776,6 +1760,17 @@ impl LintPass for Stability {
         if self.is_internal(cx, item.span) { return }
 
         match item.node {
+            ast::ItemExternCrate(_) => {
+                // compiler-generated `extern crate` items have a dummy span.
+                if item.span == DUMMY_SP { return }
+
+                let cnum = match cx.tcx.sess.cstore.find_extern_mod_stmt_cnum(item.id) {
+                    Some(cnum) => cnum,
+                    None => return,
+                };
+                let id = ast::DefId { krate: cnum, node: ast::CRATE_NODE_ID };
+                self.lint(cx, id, item.span);
+            }
             ast::ItemTrait(_, _, ref supertraits, _) => {
                 for t in supertraits.iter() {
                     if let ast::TraitTyParamBound(ref t, _) = *t {

src/librustc/lint/context.rs

@@ -603,14 +603,6 @@ impl<'a, 'tcx, 'v> Visitor<'v> for Context<'a, 'tcx> {
         })
     }
 
-    fn visit_view_item(&mut self, i: &ast::ViewItem) {
-        self.with_lint_attrs(&i.attrs[], |cx| {
-            run_lints!(cx, check_view_item, i);
-            cx.visit_ids(|v| v.visit_view_item(i));
-            visit::walk_view_item(cx, i);
-        })
-    }
-
     fn visit_pat(&mut self, p: &ast::Pat) {
         run_lints!(self, check_pat, p);
         visit::walk_pat(self, p);

src/librustc/lint/mod.rs

@@ -128,7 +128,6 @@ pub trait LintPass {
     fn check_crate(&mut self, _: &Context, _: &ast::Crate) { }
     fn check_ident(&mut self, _: &Context, _: Span, _: ast::Ident) { }
     fn check_mod(&mut self, _: &Context, _: &ast::Mod, _: Span, _: ast::NodeId) { }
-    fn check_view_item(&mut self, _: &Context, _: &ast::ViewItem) { }
     fn check_foreign_item(&mut self, _: &Context, _: &ast::ForeignItem) { }
     fn check_item(&mut self, _: &Context, _: &ast::Item) { }
     fn check_local(&mut self, _: &Context, _: &ast::Local) { }

src/librustc/metadata/creader.rs

@@ -40,10 +40,6 @@ pub struct CrateReader<'a> {
 }
 
 impl<'a, 'v> visit::Visitor<'v> for CrateReader<'a> {
-    fn visit_view_item(&mut self, a: &ast::ViewItem) {
-        self.process_view_item(a);
-        visit::walk_view_item(self, a);
-    }
     fn visit_item(&mut self, a: &ast::Item) {
         self.process_item(a);
         visit::walk_item(self, a);
@@ -64,9 +60,8 @@ fn dump_crates(cstore: &CStore) {
     })
 }
 
-fn should_link(i: &ast::ViewItem) -> bool {
+fn should_link(i: &ast::Item) -> bool {
     !attr::contains_name(&i.attrs[], "no_link")
-
 }
 
 struct CrateInfo {
@@ -181,29 +176,10 @@ impl<'a> CrateReader<'a> {
         }
     }
 
-    fn process_view_item(&mut self, i: &ast::ViewItem) {
-        if !should_link(i) {
-            return;
-        }
-
-        match self.extract_crate_info(i) {
-            Some(info) => {
-                let (cnum, _, _) = self.resolve_crate(&None,
-                                                      &info.ident[],
-                                                      &info.name[],
-                                                      None,
-                                                      i.span,
-                                                      PathKind::Crate);
-                self.sess.cstore.add_extern_mod_stmt_cnum(info.id, cnum);
-            }
-            None => ()
-        }
-    }
-
-    fn extract_crate_info(&self, i: &ast::ViewItem) -> Option<CrateInfo> {
+    fn extract_crate_info(&self, i: &ast::Item) -> Option<CrateInfo> {
         match i.node {
-            ast::ViewItemExternCrate(ident, ref path_opt, id) => {
-                let ident = token::get_ident(ident);
+            ast::ItemExternCrate(ref path_opt) => {
+                let ident = token::get_ident(i.ident);
                 debug!("resolving extern crate stmt. ident: {} path_opt: {:?}",
                        ident, path_opt);
                 let name = match *path_opt {
@@ -218,16 +194,34 @@ impl<'a> CrateReader<'a> {
                 Some(CrateInfo {
                     ident: ident.get().to_string(),
                     name: name,
-                    id: id,
+                    id: i.id,
                     should_link: should_link(i),
                 })
             }
             _ => None
         }
     }
 
-    fn process_item(&self, i: &ast::Item) {
+    fn process_item(&mut self, i: &ast::Item) {
         match i.node {
+            ast::ItemExternCrate(_) => {
+                if !should_link(i) {
+                    return;
+                }
+
+                match self.extract_crate_info(i) {
+                    Some(info) => {
+                        let (cnum, _, _) = self.resolve_crate(&None,
+                                                              &info.ident[],
+                                                              &info.name[],
+                                                              None,
+                                                              i.span,
+                                                              PathKind::Crate);
+                        self.sess.cstore.add_extern_mod_stmt_cnum(info.id, cnum);
+                    }
+                    None => ()
+                }
+            }
             ast::ItemForeignMod(ref fm) => {
                 if fm.abi == abi::Rust || fm.abi == abi::RustIntrinsic {
                     return;
@@ -533,7 +527,7 @@ impl<'a> CrateReader<'a> {
 
 #[derive(Copy)]
 pub enum CrateOrString<'a> {
-    Krate(&'a ast::ViewItem),
+    Krate(&'a ast::Item),
     Str(&'a str)
 }
 

src/librustc/metadata/encoder.rs

@@ -1456,8 +1456,8 @@ fn encode_info_for_item(ecx: &EncodeContext,
             rbml_w.end_tag();
         }
       }
-      ast::ItemMac(..) => {
-        // macros are encoded separately
+      ast::ItemExternCrate(_) | ast::ItemUse(_) |ast::ItemMac(..) => {
+        // these are encoded separately
       }
     }
 }

src/librustc/middle/astencode.rs

@@ -332,8 +332,6 @@ impl Folder for NestedItemsDropper {
                 }
             }).collect();
             let blk_sans_items = P(ast::Block {
-                view_items: Vec::new(), // I don't know if we need the view_items
-                                        // here, but it doesn't break tests!
                 stmts: stmts_sans_items,
                 expr: expr,
                 id: id,

src/librustc/middle/reachable.rs

@@ -297,6 +297,7 @@ impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
                     // These are normal, nothing reachable about these
                     // inherently and their children are already in the
                     // worklist, as determined by the privacy pass
+                    ast::ItemExternCrate(_) | ast::ItemUse(_) |
                     ast::ItemTy(..) | ast::ItemStatic(_, _, _) |
                     ast::ItemMod(..) | ast::ItemForeignMod(..) |
                     ast::ItemImpl(..) | ast::ItemTrait(..) |

src/librustc/middle/resolve_lifetime.rs

@@ -94,6 +94,8 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
                     // Fn lifetimes get added in visit_fn below:
                     visit::walk_item(this, item);
                 }
+                ast::ItemExternCrate(_) |
+                ast::ItemUse(_) |
                 ast::ItemMod(..) |
                 ast::ItemMac(..) |
                 ast::ItemForeignMod(..) |

src/librustc/plugin/load.rs

@@ -73,8 +73,10 @@ pub fn load_plugins(sess: &Session, krate: &ast::Crate,
     // We need to error on `#[macro_use] extern crate` when it isn't at the
     // crate root, because `$crate` won't work properly. Identify these by
     // spans, because the crate map isn't set up yet.
-    for vi in krate.module.view_items.iter() {
-        loader.span_whitelist.insert(vi.span);
+    for item in krate.module.items.iter() {
+        if let ast::ItemExternCrate(_) = item.node {
+            loader.span_whitelist.insert(item.span);
+        }
     }
 
     visit::walk_crate(&mut loader, krate);
@@ -91,18 +93,21 @@ pub fn load_plugins(sess: &Session, krate: &ast::Crate,
 
 // note that macros aren't expanded yet, and therefore macros can't add plugins.
 impl<'a, 'v> Visitor<'v> for PluginLoader<'a> {
-    fn visit_view_item(&mut self, vi: &ast::ViewItem) {
+    fn visit_item(&mut self, item: &ast::Item) {
         // We're only interested in `extern crate`.
-        match vi.node {
-            ast::ViewItemExternCrate(..) => (),
-            _ => return,
+        match item.node {
+            ast::ItemExternCrate(_) => {}
+            _ => {
+                visit::walk_item(self, item);
+                return;
+            }
         }
 
         // Parse the attributes relating to macro / plugin loading.
         let mut plugin_attr = None;
         let mut macro_selection = Some(HashSet::new());  // None => load all
         let mut reexport = HashSet::new();
-        for attr in vi.attrs.iter() {
+        for attr in item.attrs.iter() {
             let mut used = true;
             match attr.name().get() {
                 "phase" => {
@@ -155,7 +160,10 @@ impl<'a, 'v> Visitor<'v> for PluginLoader<'a> {
             }
         }
 
-        self.load_plugin(CrateOrString::Krate(vi), plugin_attr, macro_selection, Some(reexport))
+        self.load_plugin(CrateOrString::Krate(item),
+                         plugin_attr,
+                         macro_selection,
+                         Some(reexport))
     }
 
     fn visit_mac(&mut self, _: &ast::Mac) {

src/librustc_back/svh.rs

@@ -188,7 +188,6 @@ mod svh_visitor {
         SawLifetimeDef(token::InternedString),
 
         SawMod,
-        SawViewItem,
         SawForeignItem,
         SawItem,
         SawDecl,
@@ -436,19 +435,6 @@ mod svh_visitor {
             SawStmt(saw_stmt(&s.node)).hash(self.st); visit::walk_stmt(self, s)
         }
 
-        fn visit_view_item(&mut self, i: &ViewItem) {
-            // Two kinds of view items can affect the ABI for a crate:
-            // exported `pub use` view items (since that may expose
-            // items that downstream crates can call), and `use
-            // foo::Trait`, since changing that may affect method
-            // resolution.
-            //
-            // The simplest approach to handling both of the above is
-            // just to adopt the same simple-minded (fine-grained)
-            // hash that I am deploying elsewhere here.
-            SawViewItem.hash(self.st); visit::walk_view_item(self, i)
-        }
-
         fn visit_foreign_item(&mut self, i: &ForeignItem) {
             // FIXME (#14132) ideally we would incorporate privacy (or
             // perhaps reachability) somewhere here, so foreign items

src/librustc_driver/pretty.rs

@@ -477,7 +477,7 @@ impl fold::Folder for ReplaceBodyWithLoop {
                          e: Option<P<ast::Expr>>) -> P<ast::Block> {
             P(ast::Block {
                 expr: e,
-                view_items: vec![], stmts: vec![], rules: rules,
+                stmts: vec![], rules: rules,
                 id: ast::DUMMY_NODE_ID, span: codemap::DUMMY_SP,
             })
         }