Remove char::to_titlecase. Fix #26555

I added it because it was easy (same a `char::to_lowercase`,
just a different table), but it doesn’t make sense to have this
in std but not str::to_titlecase, which would require
https://github.com/unicode-rs/unicode-segmentation

At some point in the future this feature will be available
(both on char and str) in a crates.io crate.

Author: SimonSapin

src/etc/unicode.py

@@ -372,13 +372,6 @@ def emit_conversions_module(f, to_upper, to_lower, to_title):
         }
     }
 
-    pub fn to_title(c: char) -> [char; 3] {
-        match bsearch_case_table(c, to_titlecase_table) {
-            None        => [c, '\\0', '\\0'],
-            Some(index) => to_titlecase_table[index].1
-        }
-    }
-
     fn bsearch_case_table(c: char, table: &'static [(char, [char; 3])]) -> Option<usize> {
         match table.binary_search_by(|&(key, _)| {
             if c == key { Equal }
@@ -400,9 +393,6 @@ def emit_conversions_module(f, to_upper, to_lower, to_title):
     emit_table(f, "to_uppercase_table",
         sorted(to_upper.iteritems(), key=operator.itemgetter(0)),
         is_pub=False, t_type = t_type, pfun=pfun)
-    emit_table(f, "to_titlecase_table",
-        sorted(to_title.iteritems(), key=operator.itemgetter(0)),
-        is_pub=False, t_type = t_type, pfun=pfun)
     f.write("}\n\n")
 
 def emit_grapheme_module(f, grapheme_table, grapheme_cats):

src/libcoretest/char.rs

@@ -102,29 +102,6 @@ fn test_to_uppercase() {
     assert_eq!(upper('ᾀ'), ['Ἀ', 'Ι']);
 }
 
-#[test]
-fn test_to_titlecase() {
-    fn title(c: char) -> Vec<char> {
-        c.to_titlecase().collect()
-    }
-    assert_eq!(title('a'), ['A']);
-    assert_eq!(title('ö'), ['Ö']);
-    assert_eq!(title('ß'), ['S', 's']); // not ẞ: Latin capital letter sharp s
-    assert_eq!(title('ü'), ['Ü']);
-    assert_eq!(title('💩'), ['💩']);
-
-    assert_eq!(title('σ'), ['Σ']);
-    assert_eq!(title('τ'), ['Τ']);
-    assert_eq!(title('ι'), ['Ι']);
-    assert_eq!(title('γ'), ['Γ']);
-    assert_eq!(title('μ'), ['Μ']);
-    assert_eq!(title('α'), ['Α']);
-    assert_eq!(title('ς'), ['Σ']);
-    assert_eq!(title('DŽ'), ['Dž']);
-    assert_eq!(title('fi'), ['F', 'i']);
-    assert_eq!(title('ᾀ'), ['ᾈ']);
-}
-
 #[test]
 fn test_is_control() {
     assert!('\u{0}'.is_control());

src/librustc_unicode/char.rs

@@ -67,18 +67,6 @@ impl Iterator for ToUppercase {
     fn next(&mut self) -> Option<char> { self.0.next() }
 }
 
-/// An iterator over the titlecase mapping of a given character, returned from
-/// the [`to_titlecase` method](../primitive.char.html#method.to_titlecase) on
-/// characters.
-#[unstable(feature = "unicode", reason = "recently added")]
-pub struct ToTitlecase(CaseMappingIter);
-
-#[stable(feature = "unicode_case_mapping", since = "1.2.0")]
-impl Iterator for ToTitlecase {
-    type Item = char;
-    fn next(&mut self) -> Option<char> { self.0.next() }
-}
-
 
 enum CaseMappingIter {
     Three(char, char, char),
@@ -477,27 +465,6 @@ impl char {
         ToLowercase(CaseMappingIter::new(conversions::to_lower(self)))
     }
 
-    /// Converts a character to its titlecase equivalent.
-    ///
-    /// This performs complex unconditional mappings with no tailoring.
-    /// See `to_uppercase()` for references and more information.
-    ///
-    /// This differs from `to_uppercase()` since Unicode contains
-    /// digraphs and ligature characters.
-    /// For example, U+01F3 “dz” and U+FB01 “fi”
-    /// map to U+01F1 “DZ” and U+0046 U+0069 “Fi”, respectively.
-    ///
-    /// # Return value
-    ///
-    /// Returns an iterator which yields the characters corresponding to the
-    /// titlecase equivalent of the character. If no conversion is possible then
-    /// an iterator with just the input character is returned.
-    #[unstable(feature = "unicode", reason = "recently added")]
-    #[inline]
-    pub fn to_titlecase(self) -> ToTitlecase {
-        ToTitlecase(CaseMappingIter::new(conversions::to_title(self)))
-    }
-
     /// Converts a character to its uppercase equivalent.
     ///
     /// This performs complex unconditional mappings with no tailoring: