syntax: Tweak parsing lifetime bounds on closures

In summary these are some example transitions this change makes:

    'a ||       => ||: 'a
    proc:Send() => proc():Send

The intended syntax for closures is to put the lifetime bound not at the front
but rather in the list of bounds. Currently there is no official support in the
AST for bounds that are not 'static, so this case is currently specially handled
in the parser to desugar to what the AST is expecting. Additionally, this moves
the bounds on procedures to the correct position, which is after the argument
list.

The current grammar for closures and procedures is:

    procedure := 'proc' [ '<' lifetime-list '>' ] '(' arg-list ')'
                        [ ':' bound-list ] [ '->' type ]
    closure := [ 'unsafe' ] ['<' lifetime-list '>' ] '|' arg-list '|'
                        [ ':' bound-list ] [ '->' type ]
    lifetime-list := lifetime | lifetime ',' lifetime-list
    arg-list := ident ':' type | ident ':' type ',' arg-list
    bound-list := bound | bound '+' bound-list
    bound := path | lifetime

This does not currently handle the << ambiguity in `Option<<'a>||>`, I am
deferring that to a later patch. Additionally, this removes the support for the
obsolete syntaxes of ~fn and &fn.

Closes rust-lang#10553
Closes rust-lang#10767
Closes rust-lang#11209
Closes rust-lang#11210
Closes rust-lang#11211

Author: alexcrichton

src/doc/rust.md

@@ -3327,8 +3327,21 @@ x = bo(5,7);
 
 ### Closure types
 
-The type of a closure mapping an input of type `A` to an output of type `B` is `|A| -> B`. A closure with no arguments or return values has type `||`.
+~~~~ {.notrust .ebnf .notation}
+closure_type := [ 'unsafe' ] [ '<' lifetime-list '>' ] '|' arg-list '|'
+                [ ':' bound-list ] [ '->' type ]
+procedure_type := 'proc' [ '<' lifetime-list '>' ] '(' arg-list ')'
+                  [ ':' bound-list ] [ '->' type ]
+lifetime-list := lifetime | lifetime ',' lifetime-list
+arg-list := ident ':' type | ident ':' type ',' arg-list
+bound-list := bound | bound '+' bound-list
+bound := path | lifetime
+~~~~
 
+The type of a closure mapping an input of type `A` to an output of type `B` is
+`|A| -> B`. A closure with no arguments or return values has type `||`.
+Similarly, a procedure mapping `A` to `B` is `proc(A) -> B` and a no-argument
+and no-return value closure has type `proc()`.
 
 An example of creating and calling a closure:
 
@@ -3351,6 +3364,30 @@ call_closure(closure_no_args, closure_args);
 
 ```
 
+Unlike closures, procedures may only be invoked once, but own their
+environment, and are allowed to move out of their environment. Procedures are
+allocated on the heap (unlike closures). An example of creating and calling a
+procedure:
+
+```rust
+let string = ~"Hello";
+
+// Creates a new procedure, passing it to the `spawn` function.
+spawn(proc() {
+  println!("{} world!", string);
+})
+
+// the variable `string` has been moved into the previous procedure, so it is
+// no longer usable.
+
+
+// Create an invoke a procedure. Note that the procedure is *moved* when
+// invoked, so it cannot be invoked again.
+let f = proc(n) { n + 22 };
+println!("answer: {}", f(20));
+
+```
+
 ### Object types
 
 Every trait item (see [traits](#traits)) defines a type with the same name as the trait.

src/libsyntax/parse/obsolete.rs

@@ -36,8 +36,6 @@ pub enum ObsoleteSyntax {
     ObsoleteEnumWildcard,
     ObsoleteStructWildcard,
     ObsoleteVecDotDotWildcard,
-    ObsoleteBoxedClosure,
-    ObsoleteClosureType,
     ObsoleteMultipleImport,
     ObsoleteManagedPattern,
     ObsoleteManagedString,
@@ -111,16 +109,6 @@ impl<'a> ParserObsoleteMethods for Parser<'a> {
                 "vec slice wildcard",
                 "use `..` instead of `.._` for matching slices"
             ),
-            ObsoleteBoxedClosure => (
-                "managed or owned closure",
-                "managed closures have been removed and owned closures are \
-                 now written `proc()`"
-            ),
-            ObsoleteClosureType => (
-                "closure type",
-                "closures are now written `|A| -> B` rather than `&fn(A) -> \
-                 B`."
-            ),
             ObsoleteMultipleImport => (
                 "multiple imports",
                 "only one import is allowed per `use` statement"