libsyntax: Accept use foo as bar; in lieu of use bar as foo;

The old syntax will be removed after a snapshot.

RFC #47.

Issue #16461.

Author: pcwalton

src/doc/rust.md

@@ -919,7 +919,7 @@ extern crate foo = "some/where/rust-foo#foo:1.0"; // a full crate ID for externa
 ##### Use declarations
 
 ~~~~ {.ebnf .gram}
-use_decl : "pub" ? "use" [ ident '=' path
+use_decl : "pub" ? "use" [ path "as" ident
                           | path_glob ] ;
 
 path_glob : ident [ "::" [ path_glob
@@ -939,7 +939,7 @@ module item. These declarations may appear at the top of [modules](#modules) and
 
 Use declarations support a number of convenient shortcuts:
 
-  * Rebinding the target name as a new local name, using the syntax `use x = p::q::r;`.
+  * Rebinding the target name as a new local name, using the syntax `use p::q::r as x;`.
   * Simultaneously binding a list of paths differing only in their final element,
     using the glob-like brace syntax `use a::b::{c,d,e,f};`
   * Binding all paths matching a given prefix, using the asterisk wildcard syntax `use a::b::*;`

src/libsyntax/ast.rs

@@ -1114,11 +1114,11 @@ pub type ViewPath = Spanned<ViewPath_>;
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)]
 pub enum ViewPath_ {
 
-    /// `quux = foo::bar::baz`
+    /// `foo::bar::baz as quux`
     ///
     /// or just
     ///
-    /// `foo::bar::baz ` (with 'baz =' implicitly on the left)
+    /// `foo::bar::baz` (with `as baz` implicitly on the right)
     ViewPathSimple(Ident, Path, NodeId),
 
     /// `foo::bar::*`

src/libsyntax/parse/parser.rs

@@ -5309,6 +5309,7 @@ impl<'a> Parser<'a> {
         match self.token {
           token::EQ => {
             // x = foo::bar
+            // NOTE(stage0, #16461, pcwalton): Deprecate after snapshot.
             self.bump();
             let path_lo = self.span.lo;
             path = vec!(self.parse_ident());
@@ -5391,7 +5392,7 @@ impl<'a> Parser<'a> {
           }
           _ => ()
         }
-        let last = *path.get(path.len() - 1u);
+        let mut rename_to = *path.get(path.len() - 1u);
         let path = ast::Path {
             span: mk_sp(lo, self.span.hi),
             global: false,
@@ -5403,9 +5404,12 @@ impl<'a> Parser<'a> {
                 }
             }).collect()
         };
+        if self.eat_keyword(keywords::As) {
+            rename_to = self.parse_ident()
+        }
         return box(GC) spanned(lo,
                         self.last_span.hi,
-                        ViewPathSimple(last, path, ast::DUMMY_NODE_ID));
+                        ViewPathSimple(rename_to, path, ast::DUMMY_NODE_ID));
     }
 
     /// Parses a sequence of items. Stops when it finds program

src/libsyntax/print/pprust.rs

@@ -2262,13 +2262,17 @@ impl<'a> State<'a> {
     pub fn print_view_path(&mut self, vp: &ast::ViewPath) -> IoResult<()> {
         match vp.node {
             ast::ViewPathSimple(ident, ref path, _) => {
+                try!(self.print_path(path, false));
+
                 // FIXME(#6993) can't compare identifiers directly here
-                if path.segments.last().unwrap().identifier.name != ident.name {
-                    try!(self.print_ident(ident));
+                if path.segments.last().unwrap().identifier.name !=
+                        ident.name {
                     try!(space(&mut self.s));
-                    try!(self.word_space("="));
+                    try!(self.word_space("as"));
+                    try!(self.print_ident(ident));
                 }
-                self.print_path(path, false)
+
+                Ok(())
             }
 
             ast::ViewPathGlob(ref path, _) => {

src/test/auxiliary/privacy_reexport.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-pub use bar = foo;
+pub use foo as bar;
 
 mod foo {
     pub fn frob() {}

src/test/auxiliary/reexported_static_methods.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 pub use sub_foo::Foo;
-pub use Baz = self::Bar;
+pub use self::Bar as Baz;
 pub use sub_foo::Boz;
 pub use sub_foo::Bort;
 

src/test/auxiliary/static_priv_by_default.rs

@@ -39,10 +39,10 @@ mod foo {
 }
 
 pub mod bar {
-    pub use e = foo::reexported_a;
-    pub use f = foo::reexported_b;
-    pub use g = foo::reexported_c;
-    pub use h = foo::reexported_d;
+    pub use foo::reexported_a as e;
+    pub use foo::reexported_b as f;
+    pub use foo::reexported_c as g;
+    pub use foo::reexported_d as h;
 }
 
 pub static a: int = 0;

src/test/compile-fail/borrowck-struct-update-with-dtor.rs

@@ -12,7 +12,7 @@
 // move, when the struct implements Drop.
 
 // NoCopy
-use NP = std::kinds::marker::NoCopy;
+use std::kinds::marker::NoCopy as NP;
 
 
 struct S { a: int, np: NP }

src/test/compile-fail/glob-resolve1.rs

@@ -15,7 +15,7 @@
 use bar::*;
 
 mod bar {
-    use import = self::fpriv;
+    use self::fpriv as import;
     fn fpriv() {}
     extern {
         fn epriv();

src/test/compile-fail/import-from-rename.rs

@@ -10,7 +10,7 @@
 
 // error-pattern:expected
 
-use baz = foo::{bar};
+use foo::{bar} as baz;
 
 mod foo {
     pub fn bar() {}