Make unaccent handle all diacritics known to Unicode, and expand ligatures correctly

Add Python script for buiding unaccent.rules from Unicode data. Don't
backpatch because unaccent changes may require tsvector/index
rebuild.

Thomas Munro <thomas.munro@enterprisedb.com>

Author: feodor

contrib/unaccent/generate_unaccent_rules.py

@@ -0,0 +1,123 @@
+#!/usr/bin/python
+#
+# This script builds unaccent.rules on standard output when given the
+# contents of UnicodeData.txt[1] on standard input.  Optionally includes
+# ligature expansion, if --expand-ligatures is given on the command line.
+#
+# The approach is to use the Unicode decomposition data to identify
+# precomposed codepoints that are equivalent to a ligature of several
+# letters, or a base letter with any number of diacritical marks.
+# There is also a small set of special cases for codepoints that we
+# traditionally support even though Unicode doesn't consider them to
+# be ligatures or letters with marks.
+#
+# [1] http://unicode.org/Public/7.0.0/ucd/UnicodeData.txt
+
+import re
+import sys
+
+def print_record(codepoint, letter):
+    print (unichr(codepoint) + "\t" + letter).encode("UTF-8")
+
+class Codepoint:
+    def __init__(self, id, general_category, combining_ids):
+        self.id = id
+        self.general_category = general_category
+        self.combining_ids = combining_ids
+
+def is_plain_letter(codepoint):
+    """Return true if codepoint represents a plain ASCII letter."""
+    return (codepoint.id >= ord('a') and codepoint.id <= ord('z')) or \
+           (codepoint.id >= ord('A') and codepoint.id <= ord('Z'))
+
+def is_mark(codepoint):
+    """Returns true for diacritical marks (combining codepoints)."""
+    return codepoint.general_category in ("Mn", "Me", "Mc")
+
+def is_letter_with_marks(codepoint, table):
+    """Returns true for plain letters combined with one or more marks."""
+    # See http://www.unicode.org/reports/tr44/tr44-14.html#General_Category_Values
+    return len(codepoint.combining_ids) > 1 and \
+           is_plain_letter(table[codepoint.combining_ids[0]]) and \
+           all(is_mark(table[i]) for i in codepoint.combining_ids[1:])
+
+def is_letter(codepoint, table):
+    """Return true for letter with or without diacritical marks."""
+    return is_plain_letter(codepoint) or is_letter_with_marks(codepoint, table)
+
+def get_plain_letter(codepoint, table):
+    """Return the base codepoint without marks."""
+    if is_letter_with_marks(codepoint, table):
+        return table[codepoint.combining_ids[0]]
+    elif is_plain_letter(codepoint):
+        return codepoint
+    else:
+        raise "mu"
+
+def is_ligature(codepoint, table):
+    """Return true for letters combined with letters."""
+    return all(is_letter(table[i], table) for i in codepoint.combining_ids)
+
+def get_plain_letters(codepoint, table):
+    """Return a list of plain letters from a ligature."""
+    assert(is_ligature(codepoint, table))
+    return [get_plain_letter(table[id], table) for id in codepoint.combining_ids]
+
+def main(expand_ligatures):
+    # http://www.unicode.org/reports/tr44/tr44-14.html#Character_Decomposition_Mappings
+    decomposition_type_pattern = re.compile(" *<[^>]*> *")
+
+    table = {}
+    all = []
+
+    # read everything we need into memory
+    for line in sys.stdin.readlines():
+        fields = line.split(";")
+        if len(fields) > 5:
+            # http://www.unicode.org/reports/tr44/tr44-14.html#UnicodeData.txt
+            general_category = fields[2]
+            decomposition = fields[5]
+            decomposition = re.sub(decomposition_type_pattern, ' ', decomposition)
+            id = int(fields[0], 16)
+            combining_ids = [int(s, 16) for s in decomposition.split(" ") if s != ""]
+            codepoint = Codepoint(id, general_category, combining_ids)
+            table[id] = codepoint
+            all.append(codepoint)
+
+    # walk through all the codepoints looking for interesting mappings
+    for codepoint in all:
+        if codepoint.general_category.startswith('L') and \
+           len(codepoint.combining_ids) > 1:
+            if is_letter_with_marks(codepoint, table):
+                print_record(codepoint.id,
+                             chr(get_plain_letter(codepoint, table).id))
+            elif expand_ligatures and is_ligature(codepoint, table):
+                print_record(codepoint.id,
+                             "".join(unichr(combining_codepoint.id)
+                                     for combining_codepoint \
+                                     in get_plain_letters(codepoint, table)))
+
+    # some special cases
+    print_record(0x00d8, "O") # LATIN CAPITAL LETTER O WITH STROKE
+    print_record(0x00f8, "o") # LATIN SMALL LETTER O WITH STROKE
+    print_record(0x0110, "D") # LATIN CAPITAL LETTER D WITH STROKE
+    print_record(0x0111, "d") # LATIN SMALL LETTER D WITH STROKE
+    print_record(0x0131, "i") # LATIN SMALL LETTER DOTLESS I
+    print_record(0x0126, "H") # LATIN CAPITAL LETTER H WITH STROKE
+    print_record(0x0127, "h") # LATIN SMALL LETTER H WITH STROKE
+    print_record(0x0141, "L") # LATIN CAPITAL LETTER L WITH STROKE
+    print_record(0x0142, "l") # LATIN SMALL LETTER L WITH STROKE
+    print_record(0x0149, "'n") # LATIN SMALL LETTER N PRECEDED BY APOSTROPHE
+    print_record(0x0166, "T") # LATIN CAPITAL LETTER T WITH STROKE
+    print_record(0x0167, "t") # LATIN SMALL LETTER t WITH STROKE
+    print_record(0x0401, u"\u0415") # CYRILLIC CAPITAL LETTER IO
+    print_record(0x0451, u"\u0435") # CYRILLIC SMALL LETTER IO
+    if expand_ligatures:
+        print_record(0x00c6, "AE") # LATIN CAPITAL LETTER AE
+        print_record(0x00df, "ss") # LATIN SMALL LETTER SHARP S
+        print_record(0x00e6, "ae") # LATIN SMALL LETTER AE
+        print_record(0x0152, "OE") # LATIN CAPITAL LIGATURE OE
+        print_record(0x0153, "oe") # LATIN SMALL LIGATURE OE
+
+if __name__ == "__main__":
+    main(len(sys.argv) == 2 and sys.argv[1] == "--expand-ligatures")