Auto merge of #21947 - bluss:full-range-syntax, r=brson

Implement step 1 of rust-lang/rfcs#702

Allows the expression `..` (without either endpoint) in general, can be
used in slicing syntax `&expr[..]` where we previously wrote `&expr[]`.

The old syntax &expr[] is not yet removed or warned for.

Author: bors

src/libsyntax/parse/parser.rs

@@ -2527,16 +2527,7 @@ impl<'a> Parser<'a> {
                 let bracket_pos = self.span.lo;
                 self.bump();
 
-                let mut found_dotdot = false;
-                if self.token == token::DotDot &&
-                   self.look_ahead(1, |t| t == &token::CloseDelim(token::Bracket)) {
-                    // Using expr[..], which is a mistake, should be expr[]
-                    self.bump();
-                    self.bump();
-                    found_dotdot = true;
-                }
-
-                if found_dotdot || self.eat(&token::CloseDelim(token::Bracket)) {
+                if self.eat(&token::CloseDelim(token::Bracket)) {
                     // No expression, expand to a RangeFull
                     // FIXME(#20516) It would be better to use a lang item or
                     // something for RangeFull.
@@ -2560,7 +2551,11 @@ impl<'a> Parser<'a> {
                     let range = ExprStruct(path, vec![], None);
                     let ix = self.mk_expr(bracket_pos, hi, range);
                     let index = self.mk_index(e, ix);
-                    e = self.mk_expr(lo, hi, index)
+                    e = self.mk_expr(lo, hi, index);
+                    // Enable after snapshot.
+                    // self.span_warn(e.span, "deprecated slicing syntax: `[]`");
+                    // self.span_note(e.span,
+                    //               "use `&expr[..]` to construct a slice of the whole of expr");
                 } else {
                     let ix = self.parse_expr();
                     hi = self.span.hi;
@@ -2569,11 +2564,6 @@ impl<'a> Parser<'a> {
                     e = self.mk_expr(lo, hi, index)
                 }
 
-                if found_dotdot {
-                    self.span_err(e.span, "incorrect slicing expression: `[..]`");
-                    self.span_note(e.span,
-                                   "use `&expr[]` to construct a slice of the whole of expr");
-                }
               }
               _ => return e
             }
@@ -2934,9 +2924,14 @@ impl<'a> Parser<'a> {
             // with the postfix-form 'expr..'
             let lo = self.span.lo;
             self.bump();
-            let rhs = self.parse_binops();
-            let hi = rhs.span.hi;
-            let ex = self.mk_range(None, Some(rhs));
+            let opt_end = if self.is_at_start_of_range_notation_rhs() {
+                let end = self.parse_binops();
+                Some(end)
+            } else {
+                None
+            };
+            let hi = self.span.hi;
+            let ex = self.mk_range(None, opt_end);
             self.mk_expr(lo, hi, ex)
           }
           _ => {

src/libsyntax/print/pprust.rs

@@ -1811,9 +1811,7 @@ impl<'a> State<'a> {
                 if let &Some(ref e) = start {
                     try!(self.print_expr(&**e));
                 }
-                if start.is_some() || end.is_some() {
-                    try!(word(&mut self.s, ".."));
-                }
+                try!(word(&mut self.s, ".."));
                 if let &Some(ref e) = end {
                     try!(self.print_expr(&**e));
                 }

src/test/bench/shootout-fasta-redux.rs

@@ -180,7 +180,7 @@ impl<'a, W: Writer> RandomFasta<'a, W> {
 
     fn nextc(&mut self) -> u8 {
         let r = self.rng(1.0);
-        for a in &self.lookup[] {
+        for a in &self.lookup[..] {
             if a.p >= r {
                 return a.c;
             }

src/test/compile-fail/packed-struct-generic-transmute.rs

@@ -32,6 +32,6 @@ fn main() {
     let foo = Foo { bar: [1u8, 2, 3, 4, 5], baz: 10i32 };
     unsafe {
         let oof: Oof<[u8; 5], i32> = mem::transmute(foo);
-        println!("{:?} {:?}", &oof.rab[], oof.zab);
+        println!("{:?} {:?}", &oof.rab[..], oof.zab);
     }
 }

src/test/compile-fail/slice-1.rs

@@ -8,12 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Test slicing expr[..] is an error and gives a helpful error message.
+// Test slicing &expr[] is deprecated and gives a helpful error message.
+//
+// ignore-test
 
 struct Foo;
 
 fn main() {
     let x = Foo;
-    &x[..]; //~ ERROR incorrect slicing expression: `[..]`
-    //~^ NOTE use `&expr[]` to construct a slice of the whole of expr
+    &x[]; //~ WARNING deprecated slicing syntax: `[]`
+          //~^ NOTE use `&expr[..]` to construct a slice of the whole of expr
+          //~^^ ERROR cannot index a value of type `Foo`
 }

src/test/compile-fail/slice-2.rs

@@ -14,7 +14,7 @@ struct Foo;
 
 fn main() {
     let x = Foo;
-    &x[]; //~ ERROR cannot index a value of type `Foo`
+    &x[..]; //~ ERROR cannot index a value of type `Foo`
     &x[Foo..]; //~ ERROR cannot index a value of type `Foo`
     &x[..Foo]; //~ ERROR cannot index a value of type `Foo`
     &x[Foo..Foo]; //~ ERROR cannot index a value of type `Foo`

src/test/run-pass/auto-encode.rs

@@ -35,7 +35,7 @@ fn test_rbml<'a, 'b, A:
     let mut rbml_w = EBwriter::Encoder::new(&mut wr);
     a1.encode(&mut rbml_w);
 
-    let d: serialize::rbml::Doc<'a> = EBDoc::new(&wr[]);
+    let d: serialize::rbml::Doc<'a> = EBDoc::new(&wr);
     let mut decoder: EBReader::Decoder<'a> = EBreader::Decoder::new(d);
     let a2: A = Decodable::decode(&mut decoder);
     assert!(*a1 == a2);

src/test/run-pass/coerce-overloaded-autoderef.rs

@@ -47,19 +47,19 @@ fn use_slice(_: &[u8]) {}
 fn use_slice_mut(_: &mut [u8]) {}
 
 fn use_vec(mut v: Vec<u8>) {
-    use_slice_mut(&mut v[]); // what you have to write today
-    use_slice_mut(&mut v);   // what you'd be able to write
+    use_slice_mut(&mut v[..]); // what you have to write today
+    use_slice_mut(&mut v);     // what you'd be able to write
     use_slice_mut(&mut &mut &mut v);
 
-    use_slice(&v[]);    // what you have to write today
+    use_slice(&v[..]);  // what you have to write today
     use_slice(&v);      // what you'd be able to write
     use_slice(&&&&&&v);
     use_slice(&mut &&&&&v);
     use_slice(&&&mut &&&v);
 }
 
 fn use_vec_ref(v: &Vec<u8>) {
-    use_slice(&v[]);    // what you have to write today
+    use_slice(&v[..]);  // what you have to write today
     use_slice(v);       // what you'd be able to write
     use_slice(&&&&&&v);
     use_slice(&mut &&&&&v);

src/test/run-pass/deriving-encodable-decodable.rs

@@ -59,7 +59,7 @@ fn roundtrip<'a, T: Rand + Eq + Encodable<Encoder<'a>> +
     let mut w = Vec::new();
     let mut e = Encoder::new(&mut w);
     obj.encode(&mut e);
-    let doc = rbml::Doc::new(&w[]);
+    let doc = rbml::Doc::new(&w);
     let mut dec = Decoder::new(doc);
     let obj2 = Decodable::decode(&mut dec);
     assert!(obj == obj2);

src/test/run-pass/foreach-external-iterators-break.rs

@@ -11,7 +11,7 @@
 pub fn main() {
     let x = [1; 100];
     let mut y = 0;
-    for i in &x[] {
+    for i in &x[..] {
         if y > 10 {
             break;
         }