LibUnicode: Begin implementing special Unicode case folding

This implements unconditional special case folding, and conditional
folding for non-locale cases. Worth noting that the only conditional,
non-locale special case is for converting an uppercase sigma to
lowercase.

Tests/LibUnicode/TestUnicodeCharacterTypes.cpp

@@ -6,6 +6,7 @@
 
 #include <LibTest/TestCase.h>
 
+#include <AK/StringView.h>
 #include <LibUnicode/CharacterTypes.h>
 #include <ctype.h>
 
@@ -48,3 +49,151 @@ TEST_CASE(to_unicode_uppercase)
     EXPECT_EQ(Unicode::to_unicode_uppercase(0x3402u), 0x3402u);
     EXPECT_EQ(Unicode::to_unicode_uppercase(0x4dbfu), 0x4dbfu);
 }
+
+TEST_CASE(to_unicode_lowercase_unconditional_special_casing)
+{
+    // LATIN SMALL LETTER SHARP S
+    auto result = Unicode::to_unicode_lowercase_full("\u00DF"sv);
+    EXPECT_EQ(result, "\u00DF");
+
+    // LATIN CAPITAL LETTER I WITH DOT ABOVE
+    result = Unicode::to_unicode_lowercase_full("\u0130"sv);
+    EXPECT_EQ(result, "\u0069\u0307");
+
+    // LATIN SMALL LIGATURE FF
+    result = Unicode::to_unicode_lowercase_full("\uFB00"sv);
+    EXPECT_EQ(result, "\uFB00");
+
+    // LATIN SMALL LIGATURE FI
+    result = Unicode::to_unicode_lowercase_full("\uFB01"sv);
+    EXPECT_EQ(result, "\uFB01");
+
+    // LATIN SMALL LIGATURE FL
+    result = Unicode::to_unicode_lowercase_full("\uFB02"sv);
+    EXPECT_EQ(result, "\uFB02");
+
+    // LATIN SMALL LIGATURE FFI
+    result = Unicode::to_unicode_lowercase_full("\uFB03"sv);
+    EXPECT_EQ(result, "\uFB03");
+
+    // LATIN SMALL LIGATURE FFL
+    result = Unicode::to_unicode_lowercase_full("\uFB04"sv);
+    EXPECT_EQ(result, "\uFB04");
+
+    // LATIN SMALL LIGATURE LONG S T
+    result = Unicode::to_unicode_lowercase_full("\uFB05"sv);
+    EXPECT_EQ(result, "\uFB05");
+
+    // LATIN SMALL LIGATURE ST
+    result = Unicode::to_unicode_lowercase_full("\uFB06"sv);
+    EXPECT_EQ(result, "\uFB06");
+
+    // GREEK SMALL LETTER ALPHA WITH PERISPOMENI AND YPOGEGRAMMENI
+    result = Unicode::to_unicode_lowercase_full("\u1FB7"sv);
+    EXPECT_EQ(result, "\u1FB7");
+
+    // GREEK SMALL LETTER ETA WITH PERISPOMENI AND YPOGEGRAMMENI
+    result = Unicode::to_unicode_lowercase_full("\u1FC7"sv);
+    EXPECT_EQ(result, "\u1FC7");
+
+    // GREEK SMALL LETTER OMEGA WITH PERISPOMENI AND YPOGEGRAMMENI
+    result = Unicode::to_unicode_lowercase_full("\u1FF7"sv);
+    EXPECT_EQ(result, "\u1FF7");
+}
+
+TEST_CASE(to_unicode_lowercase_special_casing_sigma)
+{
+    auto result = Unicode::to_unicode_lowercase_full("ABCI"sv);
+    EXPECT_EQ(result, "abci");
+
+    // Sigma preceded by A
+    result = Unicode::to_unicode_lowercase_full("A\u03A3"sv);
+    EXPECT_EQ(result, "a\u03C2");
+
+    // Sigma preceded by A and MONGOLIAN VOWEL SEPARATOR
+    result = Unicode::to_unicode_lowercase_full("A\u180E\u03A3"sv);
+    EXPECT_EQ(result, "a\u180E\u03C2");
+
+    // Sigma preceded by A and MONGOLIAN VOWEL SEPARATOR, followed by B
+    result = Unicode::to_unicode_lowercase_full("A\u180E\u03A3B"sv);
+    EXPECT_EQ(result, "a\u180E\u03C3b");
+
+    // Sigma followed by A
+    result = Unicode::to_unicode_lowercase_full("\u03A3A"sv);
+    EXPECT_EQ(result, "\u03C3a");
+
+    // Sigma preceded by A, followed by MONGOLIAN VOWEL SEPARATOR
+    result = Unicode::to_unicode_lowercase_full("A\u03A3\u180E"sv);
+    EXPECT_EQ(result, "a\u03C2\u180E");
+
+    // Sigma preceded by A, followed by MONGOLIAN VOWEL SEPARATOR and B
+    result = Unicode::to_unicode_lowercase_full("A\u03A3\u180EB"sv);
+    EXPECT_EQ(result, "a\u03C3\u180Eb");
+
+    // Sigma preceded by A and MONGOLIAN VOWEL SEPARATOR, followed by MONGOLIAN VOWEL SEPARATOR
+    result = Unicode::to_unicode_lowercase_full("A\u180E\u03A3\u180E"sv);
+    EXPECT_EQ(result, "a\u180E\u03C2\u180E");
+
+    // Sigma preceded by A and MONGOLIAN VOWEL SEPARATOR, followed by MONGOLIAN VOWEL SEPARATOR and B
+    result = Unicode::to_unicode_lowercase_full("A\u180E\u03A3\u180EB"sv);
+    EXPECT_EQ(result, "a\u180E\u03C3\u180Eb");
+}
+
+TEST_CASE(to_unicode_uppercase_unconditional_special_casing)
+{
+    // LATIN SMALL LETTER SHARP S
+    auto result = Unicode::to_unicode_uppercase_full("\u00DF"sv);
+    EXPECT_EQ(result, "\u0053\u0053");
+
+    // LATIN CAPITAL LETTER I WITH DOT ABOVE
+    result = Unicode::to_unicode_uppercase_full("\u0130"sv);
+    EXPECT_EQ(result, "\u0130");
+
+    // LATIN SMALL LIGATURE FF
+    result = Unicode::to_unicode_uppercase_full("\uFB00"sv);
+    EXPECT_EQ(result, "\u0046\u0046");
+
+    // LATIN SMALL LIGATURE FI
+    result = Unicode::to_unicode_uppercase_full("\uFB01"sv);
+    EXPECT_EQ(result, "\u0046\u0049");
+
+    // LATIN SMALL LIGATURE FL
+    result = Unicode::to_unicode_uppercase_full("\uFB02"sv);
+    EXPECT_EQ(result, "\u0046\u004C");
+
+    // LATIN SMALL LIGATURE FFI
+    result = Unicode::to_unicode_uppercase_full("\uFB03"sv);
+    EXPECT_EQ(result, "\u0046\u0046\u0049");
+
+    // LATIN SMALL LIGATURE FFL
+    result = Unicode::to_unicode_uppercase_full("\uFB04"sv);
+    EXPECT_EQ(result, "\u0046\u0046\u004C");
+
+    // LATIN SMALL LIGATURE LONG S T
+    result = Unicode::to_unicode_uppercase_full("\uFB05"sv);
+    EXPECT_EQ(result, "\u0053\u0054");
+
+    // LATIN SMALL LIGATURE ST
+    result = Unicode::to_unicode_uppercase_full("\uFB06"sv);
+    EXPECT_EQ(result, "\u0053\u0054");
+
+    // GREEK SMALL LETTER IOTA WITH DIALYTIKA AND TONOS
+    result = Unicode::to_unicode_uppercase_full("\u0390"sv);
+    EXPECT_EQ(result, "\u0399\u0308\u0301");
+
+    // GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND TONOS
+    result = Unicode::to_unicode_uppercase_full("\u03B0"sv);
+    EXPECT_EQ(result, "\u03A5\u0308\u0301");
+
+    // GREEK SMALL LETTER ALPHA WITH PERISPOMENI AND YPOGEGRAMMENI
+    result = Unicode::to_unicode_uppercase_full("\u1FB7"sv);
+    EXPECT_EQ(result, "\u0391\u0342\u0399");
+
+    // GREEK SMALL LETTER ETA WITH PERISPOMENI AND YPOGEGRAMMENI
+    result = Unicode::to_unicode_uppercase_full("\u1FC7"sv);
+    EXPECT_EQ(result, "\u0397\u0342\u0399");
+
+    // GREEK SMALL LETTER OMEGA WITH PERISPOMENI AND YPOGEGRAMMENI
+    result = Unicode::to_unicode_uppercase_full("\u1FF7"sv);
+    EXPECT_EQ(result, "\u03A9\u0342\u0399");
+}