auto merge of #18603 : brson/rust/stdchar, r=aturon

* Deprecate the free functions in favor of methods, except the two ctors `from_u32` and `from_digit`, whose methods are deprecated.
* Mark the `Char` and `UnicodeChar` traits experimental until we decide for sure that we won't have some sort of inherent methods for primitives.
* The `UnicodeChar` methods related to numerics are now called e.g. `is_numeric` to match the 'numeric' unicode character class, and the `*_digit_radix` methods on `Char` now just called `*_digit`.
* `len_utf8_bytes` -> `len_utf8`
* Converted methods to take self by-value
* Converted `escape_default` and `escape_unicode` to iterators over chars.
* Renamed `is_XID_start`, `is_XID_continue` to `is_xid_start`, `is_xid_continue` to match conventions

This also converts `encode_utf8` and `encode_utf16` to return iterators. I suspect this is not the final form of these methods. Perf is worse (numbers in the commit). Many of the uses ended up being awkward, copying into a buffer then writing that buffer to a `Writer`. It might be more appropriate for these to return `Reader`s instead, but that type is defined in `std`.

Note: although I *did* add the `from_u32` ctor to the `Char` trait, I deprecated it again later, preferring the free ctors.

I've been sitting on this for a while.

cc @aturon

Author: bors

src/compiletest/runtest.rs

@@ -1566,7 +1566,7 @@ fn _arm_exec_compiled_test(config: &Config,
 
     let mut exitcode: int = 0;
     for c in exitcode_out.as_slice().chars() {
-        if !c.is_digit() { break; }
+        if !c.is_numeric() { break; }
         exitcode = exitcode * 10 + match c {
             '0' ... '9' => c as int - ('0' as int),
             _ => 101,

src/libcollections/str.rs

@@ -630,7 +630,9 @@ pub trait StrAllocating: Str {
         let me = self.as_slice();
         let mut out = String::with_capacity(me.len());
         for c in me.chars() {
-            c.escape_default(|c| out.push(c));
+            for c in c.escape_default() {
+                out.push(c);
+            }
         }
         out
     }
@@ -640,7 +642,9 @@ pub trait StrAllocating: Str {
         let me = self.as_slice();
         let mut out = String::with_capacity(me.len());
         for c in me.chars() {
-            c.escape_unicode(|c| out.push(c));
+            for c in c.escape_unicode() {
+                out.push(c);
+            }
         }
         out
     }
@@ -1189,7 +1193,7 @@ mod tests {
         assert_eq!("11foo1bar11".trim_left_chars('1'), "foo1bar11");
         let chars: &[char] = &['1', '2'];
         assert_eq!("12foo1bar12".trim_left_chars(chars), "foo1bar12");
-        assert_eq!("123foo1bar123".trim_left_chars(|c: char| c.is_digit()), "foo1bar123");
+        assert_eq!("123foo1bar123".trim_left_chars(|c: char| c.is_numeric()), "foo1bar123");
     }
 
     #[test]
@@ -1204,7 +1208,7 @@ mod tests {
         assert_eq!("11foo1bar11".trim_right_chars('1'), "11foo1bar");
         let chars: &[char] = &['1', '2'];
         assert_eq!("12foo1bar12".trim_right_chars(chars), "12foo1bar");
-        assert_eq!("123foo1bar123".trim_right_chars(|c: char| c.is_digit()), "123foo1bar");
+        assert_eq!("123foo1bar123".trim_right_chars(|c: char| c.is_numeric()), "123foo1bar");
     }
 
     #[test]
@@ -1219,7 +1223,7 @@ mod tests {
         assert_eq!("11foo1bar11".trim_chars('1'), "foo1bar");
         let chars: &[char] = &['1', '2'];
         assert_eq!("12foo1bar12".trim_chars(chars), "foo1bar");
-        assert_eq!("123foo1bar123".trim_chars(|c: char| c.is_digit()), "foo1bar");
+        assert_eq!("123foo1bar123".trim_chars(|c: char| c.is_numeric()), "foo1bar");
     }
 
     #[test]