Auto merge of #30884 - durka:inclusive-ranges, r=aturon

This PR implements [RFC 1192](https://github.com/rust-lang/rfcs/blob/master/text/1192-inclusive-ranges.md), which is triple-dot syntax for inclusive range expressions. The new stuff is behind two feature gates (one for the syntax and one for the std::ops types). This replaces the deprecated functionality in std::iter. Along the way I simplified the desugaring for all ranges.

This is my first contribution to rust which changes more than one character outside of a test or comment, so please review carefully! Some of the individual commit messages have more of my notes. Also thanks for putting up with my dumb questions in #rust-internals.

- For implementing `std::ops::RangeInclusive`, I took @Stebalien's suggestion from rust-lang/rfcs#1192 (comment). It seemed to me to make the implementation easier and increase type safety. If that stands, the RFC should be amended to avoid confusion.
- I also kind of like @glaebhoerl's [idea](rust-lang/rfcs#1254 (comment)), which is unified inclusive/exclusive range syntax something like `x>..=y`. We can experiment with this while everything is behind a feature gate.
- There are a couple of FIXMEs left (see the last commit). I didn't know what to do about `RangeArgument` and I haven't added `Index` impls yet. Those should be discussed/finished before merging.

cc @gankro since you [complained](https://www.reddit.com/r/rust/comments/3xkfro/what_happened_to_inclusive_ranges/cy5j0yq)
cc #27777 #30877 #1192 rust-lang/rfcs#1254
relevant to #28237 (tracking issue)

Author: bors

Diff for: src/doc/book/iterators.md

@@ -14,6 +14,11 @@ Now that you know more Rust, we can talk in detail about how this works.
 Ranges (the `0..10`) are 'iterators'. An iterator is something that we can
 call the `.next()` method on repeatedly, and it gives us a sequence of things.
 
+(By the way, a range with two dots like `0..10` is inclusive on the left (so it
+starts at 0) and exclusive on the right (so it ends at 9). A mathematician
+would write "[0, 10)". To get a range that goes all the way up to 10 you can
+write `0...10`.)
+
 Like this:
 
 ```rust

Diff for: src/doc/book/syntax-index.md

@@ -66,7 +66,8 @@
 * `..` (`..`, `expr..`, `..expr`, `expr..expr`): right-exclusive range literal.
 * `..` (`..expr`): struct literal update syntax.  See [Structs (Update syntax)].
 * `..` (`variant(x, ..)`, `struct_type { x, .. }`): "and the rest" pattern binding.  See [Patterns (Ignoring bindings)].
-* `...` (`expr ... expr`): inclusive range pattern.  See [Patterns (Ranges)].
+* `...` (`...expr`, `expr...expr`) *in an expression*: inclusive range expression. See [Iterators].
+* `...` (`expr...expr`) *in a pattern*: inclusive range pattern.  See [Patterns (Ranges)].
 * `/` (`expr / expr`): arithmetic division.  Overloadable (`Div`).
 * `/=` (`var /= expr`): arithmetic division & assignment.
 * `:` (`pat: type`, `ident: type`): constraints.  See [Variable Bindings], [Functions], [Structs], [Traits].
@@ -205,6 +206,7 @@
 [Functions (Early Returns)]: functions.html#early-returns
 [Functions]: functions.html
 [Generics]: generics.html
+[Iterators]: iterators.html
 [Lifetimes]: lifetimes.html
 [Loops (`for`)]: loops.html#for
 [Loops (`loop`)]: loops.html#loop

Diff for: src/doc/reference.md

@@ -2277,6 +2277,10 @@ The currently implemented features of the reference compiler are:
                     `#[derive_Foo] #[derive_Bar]`, which can be user-defined syntax
                     extensions.
 
+* `inclusive_range_syntax` - Allows use of the `a...b` and `...b` syntax for inclusive ranges.
+
+* `inclusive_range` - Allows use of the types that represent desugared inclusive ranges.
+
 * `intrinsics` - Allows use of the "rust-intrinsics" ABI. Compiler intrinsics
                  are inherently unstable and no promise about them is made.
 
@@ -2747,6 +2751,25 @@ let y = 0..10;
 assert_eq!(x, y);
 ```
 
+Similarly, the `...` operator will construct an object of one of the
+`std::ops::RangeInclusive` variants.
+
+```
+# #![feature(inclusive_range_syntax)]
+1...2;   // std::ops::RangeInclusive
+...4;    // std::ops::RangeToInclusive
+```
+
+The following expressions are equivalent.
+
+```
+# #![feature(inclusive_range_syntax, inclusive_range)]
+let x = std::ops::RangeInclusive::NonEmpty {start: 0, end: 10};
+let y = 0...10;
+
+assert_eq!(x, y);
+```
+
 ### Unary operator expressions
 
 Rust defines the following unary operators. They are all written as prefix operators,

Diff for: src/libcollections/lib.rs

@@ -40,7 +40,7 @@
 #![feature(fmt_internals)]
 #![feature(fmt_radix)]
 #![feature(heap_api)]
-#![feature(iter_arith)]
+#![feature(inclusive_range)]
 #![feature(iter_arith)]
 #![feature(lang_items)]
 #![feature(nonzero)]

Diff for: src/libcollections/range.rs

@@ -35,6 +35,7 @@ pub trait RangeArgument<T> {
     }
 }
 
+// FIXME add inclusive ranges to RangeArgument
 
 impl<T> RangeArgument<T> for RangeFull {}
 

Diff for: src/libcollections/string.rs

@@ -59,7 +59,7 @@ use core::fmt;
 use core::hash;
 use core::iter::FromIterator;
 use core::mem;
-use core::ops::{self, Add};
+use core::ops::{self, Add, Index, IndexMut};
 use core::ptr;
 use core::slice;
 use core::str::pattern::Pattern;
@@ -1606,6 +1606,24 @@ impl ops::Index<ops::RangeFull> for String {
         unsafe { str::from_utf8_unchecked(&self.vec) }
     }
 }
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl ops::Index<ops::RangeInclusive<usize>> for String {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::RangeInclusive<usize>) -> &str {
+        Index::index(&**self, index)
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl ops::Index<ops::RangeToInclusive<usize>> for String {
+    type Output = str;
+
+    #[inline]
+    fn index(&self, index: ops::RangeToInclusive<usize>) -> &str {
+        Index::index(&**self, index)
+    }
+}
 
 #[stable(feature = "derefmut_for_string", since = "1.2.0")]
 impl ops::IndexMut<ops::Range<usize>> for String {
@@ -1635,6 +1653,20 @@ impl ops::IndexMut<ops::RangeFull> for String {
         unsafe { mem::transmute(&mut *self.vec) }
     }
 }
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl ops::IndexMut<ops::RangeInclusive<usize>> for String {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut str {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl ops::IndexMut<ops::RangeToInclusive<usize>> for String {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut str {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ops::Deref for String {

Diff for: src/libcollections/vec.rs

@@ -1226,6 +1226,24 @@ impl<T> ops::Index<ops::RangeFull> for Vec<T> {
         self
     }
 }
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::Index<ops::RangeInclusive<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::RangeInclusive<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::Index<ops::RangeToInclusive<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::RangeToInclusive<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> ops::IndexMut<ops::Range<usize>> for Vec<T> {
@@ -1255,6 +1273,20 @@ impl<T> ops::IndexMut<ops::RangeFull> for Vec<T> {
         self
     }
 }
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::IndexMut<ops::RangeInclusive<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::IndexMut<ops::RangeToInclusive<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> ops::Deref for Vec<T> {