Declare &foo[] to be obsolete syntax. Modify the obsolete mechanism to

support warnings.

src/libsyntax/parse/obsolete.rs

@@ -28,6 +28,7 @@ pub enum ObsoleteSyntax {
     ProcExpr,
     ClosureType,
     ClosureKind,
+    EmptyIndex,
 }
 
 pub trait ParserObsoleteMethods {
@@ -48,35 +49,46 @@ pub trait ParserObsoleteMethods {
 impl<'a> ParserObsoleteMethods for parser::Parser<'a> {
     /// Reports an obsolete syntax non-fatal error.
     fn obsolete(&mut self, sp: Span, kind: ObsoleteSyntax) {
-        let (kind_str, desc) = match kind {
+        let (kind_str, desc, error) = match kind {
             ObsoleteSyntax::ForSized => (
                 "for Sized?",
                 "no longer required. Traits (and their `Self` type) do not have the `Sized` bound \
                  by default",
+                true,
             ),
             ObsoleteSyntax::ProcType => (
                 "the `proc` type",
                 "use unboxed closures instead",
+                true,
             ),
             ObsoleteSyntax::ProcExpr => (
                 "`proc` expression",
                 "use a `move ||` expression instead",
+                true,
             ),
             ObsoleteSyntax::ClosureType => (
                 "`|usize| -> bool` closure type",
                 "use unboxed closures instead, no type annotation needed"
+                true,
             ),
             ObsoleteSyntax::ClosureKind => (
                 "`:`, `&mut:`, or `&:`",
                 "rely on inference instead"
+                true,
             ),
             ObsoleteSyntax::Sized => (
                 "`Sized? T` for removing the `Sized` bound",
                 "write `T: ?Sized` instead"
+                true,
+            ),
+            ObsoleteSyntax::EmptyIndex => (
+                "[]",
+                "write `[..]` instead",
+                false, // warning for now
             ),
         };
 
-        self.report(sp, kind, kind_str, desc);
+        self.report(sp, kind, kind_str, desc, error);
     }
 
     /// Reports an obsolete syntax non-fatal error, and returns
@@ -90,9 +102,13 @@ impl<'a> ParserObsoleteMethods for parser::Parser<'a> {
               sp: Span,
               kind: ObsoleteSyntax,
               kind_str: &str,
-              desc: &str) {
-        self.span_err(sp,
-                      &format!("obsolete syntax: {}", kind_str)[]);
+              desc: &str,
+              error: bool) {
+        if error {
+            self.span_err(sp, &format!("obsolete syntax: {}", kind_str)[]);
+        } else {
+            self.span_warn(sp, &format!("obsolete syntax: {}", kind_str)[]);
+        }
 
         if !self.obsolete_set.contains(&kind) {
             self.sess

src/libsyntax/parse/parser.rs

@@ -2552,8 +2552,9 @@ impl<'a> Parser<'a> {
                             parameters: ast::PathParameters::none(),
                         }
                     }).collect();
+                    let span = mk_sp(lo, hi);
                     let path = ast::Path {
-                        span: mk_sp(lo, hi),
+                        span: span,
                         global: true,
                         segments: segments,
                     };
@@ -2562,10 +2563,8 @@ impl<'a> Parser<'a> {
                     let ix = self.mk_expr(bracket_pos, hi, range);
                     let index = self.mk_index(e, ix);
                     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");
+
+                    self.obsolete(span, ObsoleteSyntax::EmptyIndex);
                 } else {
                     let ix = self.parse_expr();
                     hi = self.span.hi;

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

@@ -9,14 +9,12 @@
 // except according to those terms.
 
 // Test slicing &expr[] is deprecated and gives a helpful error message.
-//
-// ignore-test
 
 struct Foo;
 
 fn main() {
     let x = Foo;
-    &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`
+    &x[];
+    //~^ WARN obsolete syntax
+    //~| ERROR cannot index
 }