Add combining characters to unaccent.rules.

Strip certain classes of combining characters, so that accents encoded
this way are removed.

Author: Hugh Ranalli
Discussion: https://postgr.es/m/15548-cef1b3f8de190d4f%40postgresql.org

contrib/unaccent/expected/unaccent.out

@@ -31,6 +31,12 @@ SELECT unaccent('˃˖˗˜');
  >+-~
 (1 row)
 
+SELECT unaccent('À');  -- Remove combining diacritical 0x0300
+ unaccent 
+----------
+ A
+(1 row)
+
 SELECT unaccent('unaccent', 'foobar');
  unaccent 
 ----------
@@ -55,6 +61,12 @@ SELECT unaccent('unaccent', '˃˖˗˜');
  >+-~
 (1 row)
 
+SELECT unaccent('unaccent', 'À');
+ unaccent 
+----------
+ A
+(1 row)
+
 SELECT ts_lexize('unaccent', 'foobar');
  ts_lexize 
 -----------
@@ -79,3 +91,9 @@ SELECT ts_lexize('unaccent', '˃˖˗˜');
  {>+-~}
 (1 row)
 
+SELECT ts_lexize('unaccent', 'À');
+ ts_lexize 
+-----------
+ {A}
+(1 row)
+

contrib/unaccent/generate_unaccent_rules.py

@@ -61,8 +61,25 @@ PLAIN_LETTER_RANGES = ((ord('a'), ord('z')), # Latin lower case
                        (0x03b1, 0x03c9),     # GREEK SMALL LETTER ALPHA, GREEK SMALL LETTER OMEGA
                        (0x0391, 0x03a9))     # GREEK CAPITAL LETTER ALPHA, GREEK CAPITAL LETTER OMEGA
 
+# Combining marks follow a "base" character, and result in a composite
+# character. Example: "U&'A\0300'"produces "À".There are three types of
+# combining marks: enclosing (Me), non-spacing combining (Mn), spacing
+# combining (Mc). We identify the ranges of marks we feel safe removing.
+# References:
+#   https://en.wikipedia.org/wiki/Combining_character
+#   https://www.unicode.org/charts/PDF/U0300.pdf
+#   https://www.unicode.org/charts/PDF/U20D0.pdf
+COMBINING_MARK_RANGES = ((0x0300, 0x0362),  # Mn: Accents, IPA
+                         (0x20dd, 0x20E0),  # Me: Symbols
+                         (0x20e2, 0x20e4),) # Me: Screen, keycap, triangle
+
 def print_record(codepoint, letter):
-    print (chr(codepoint) + "\t" + letter)
+    if letter:
+        output = chr(codepoint) + "\t" + letter
+    else:
+        output = chr(codepoint)
+
+    print(output)
 
 class Codepoint:
     def __init__(self, id, general_category, combining_ids):
@@ -70,6 +87,16 @@ class Codepoint:
         self.general_category = general_category
         self.combining_ids = combining_ids
 
+def is_mark_to_remove(codepoint):
+    """Return true if this is a combining mark to remove."""
+    if not is_mark(codepoint):
+        return False
+
+    for begin, end in COMBINING_MARK_RANGES:
+        if codepoint.id >= begin and codepoint.id <= end:
+            return True
+    return False
+
 def is_plain_letter(codepoint):
     """Return true if codepoint represents a "plain letter"."""
     for begin, end in PLAIN_LETTER_RANGES:
@@ -234,6 +261,8 @@ def main(args):
                              "".join(chr(combining_codepoint.id)
                                      for combining_codepoint \
                                      in get_plain_letters(codepoint, table))))
+        elif is_mark_to_remove(codepoint):
+            charactersSet.add((codepoint.id, None))
 
     # add CLDR Latin-ASCII characters
     if not args.noLigaturesExpansion:

contrib/unaccent/sql/unaccent.sql

@@ -9,13 +9,16 @@ SELECT unaccent('foobar');
 SELECT unaccent('ёлка');
 SELECT unaccent('ЁЖИК');
 SELECT unaccent('˃˖˗˜');
+SELECT unaccent('À');  -- Remove combining diacritical 0x0300
 
 SELECT unaccent('unaccent', 'foobar');
 SELECT unaccent('unaccent', 'ёлка');
 SELECT unaccent('unaccent', 'ЁЖИК');
 SELECT unaccent('unaccent', '˃˖˗˜');
+SELECT unaccent('unaccent', 'À');
 
 SELECT ts_lexize('unaccent', 'foobar');
 SELECT ts_lexize('unaccent', 'ёлка');
 SELECT ts_lexize('unaccent', 'ЁЖИК');
 SELECT ts_lexize('unaccent', '˃˖˗˜');
+SELECT ts_lexize('unaccent', 'À');

contrib/unaccent/unaccent.rules

@@ -414,6 +414,105 @@
 ˖	+
 ˗	-
 ˜	~
+̀
+́
+̂
+̃
+̄
+̅
+̆
+̇
+̈
+̉
+̊
+̋
+̌
+̍
+̎
+̏
+̐
+̑
+̒
+̓
+̔
+̕
+̖
+̗
+̘
+̙
+̚
+̛
+̜
+̝
+̞
+̟
+̠
+̡
+̢
+̣
+̤
+̥
+̦
+̧
+̨
+̩
+̪
+̫
+̬
+̭
+̮
+̯
+̰
+̱
+̲
+̳
+̴
+̵
+̶
+̷
+̸
+̹
+̺
+̻
+̼
+̽
+̾
+̿
+̀
+́
+͂
+̓
+̈́
+ͅ
+͆
+͇
+͈
+͉
+͊
+͋
+͌
+͍
+͎
+͏
+͐
+͑
+͒
+͓
+͔
+͕
+͖
+͗
+͘
+͙
+͚
+͛
+͜
+͝
+͞
+͟
+͠
+͡
+͢
 Ά	Α
 Έ	Ε
 Ή	Η
@@ -982,6 +1081,13 @@
 ₧	Pts
 ₹	Rs
 ₺	TL
+⃝
+⃞
+⃟
+⃠
+⃢
+⃣
+⃤
 ℀	a/c
 ℁	a/s
 ℂ	C