R/ncname.R

In selectr: Translate CSS Selectors to XPath Expressions

# Whether a namespace prefix can be written into an XPath expression.
#
# A prefix is passed through into a node test ('svg|rect' becomes
# 'svg:rect') because XPath 1.0 has no way to resolve one without the
# namespace URI, which the translator never sees. So a prefix that
# cannot be written as an XPath name has nowhere to go and is rejected
# (see stop_unsafe_prefix()). Local names need no such test: one that
# cannot be a name test folds into a name() or local-name() comparison
# instead, so they stay on the deliberately conservative ASCII-only
# is_safe_name().
#
# Which NCName: an XPath 1.0 NCName is an XML 1.0 Name without a colon,
# and XML 1.0 defined Name by the character tables in its Appendix B:
# Letter (BaseChar | Ideographic), Digit, CombiningChar and Extender.
# XML 1.0 Fifth Edition later replaced those tables with a much broader
# set of ranges - but that revision is of XML, not of XPath 1.0, and
# engines split on it. The tables below are the original ones, which is
# both the definition XPath 1.0 cites and a subset of the Fifth Edition
# set, so a prefix accepted here parses under either reading. libxml2 -
# the engine behind both the XML and the xml2 package - parses XPath
# names with the original tables and rejects, say, 'nsɂ' (U+0242).
#
# Erring narrow is safe in a way erring broad is not: a prefix rejected
# here is reported as an unsupported construct, which is what every
# non-ASCII prefix used to get, whereas one accepted here and refused by
# the evaluator is a parse failure the caller cannot attribute.

# 'BaseChar | Ideographic', minus the ASCII letters is_name_start_char()
# tests directly. Pairs of (first, last) code points, sorted and
# disjoint, so membership is a findInterval() lookup
xml_letters <- matrix(c(
    0x00C0, 0x00D6, 0x00D8, 0x00F6, 0x00F8, 0x0131, 0x0134, 0x013E, 0x0141, 0x0148,
    0x014A, 0x017E, 0x0180, 0x01C3, 0x01CD, 0x01F0, 0x01F4, 0x01F5, 0x01FA, 0x0217,
    0x0250, 0x02A8, 0x02BB, 0x02C1, 0x0386, 0x0386, 0x0388, 0x038A, 0x038C, 0x038C,
    0x038E, 0x03A1, 0x03A3, 0x03CE, 0x03D0, 0x03D6, 0x03DA, 0x03DA, 0x03DC, 0x03DC,
    0x03DE, 0x03DE, 0x03E0, 0x03E0, 0x03E2, 0x03F3, 0x0401, 0x040C, 0x040E, 0x044F,
    0x0451, 0x045C, 0x045E, 0x0481, 0x0490, 0x04C4, 0x04C7, 0x04C8, 0x04CB, 0x04CC,
    0x04D0, 0x04EB, 0x04EE, 0x04F5, 0x04F8, 0x04F9, 0x0531, 0x0556, 0x0559, 0x0559,
    0x0561, 0x0586, 0x05D0, 0x05EA, 0x05F0, 0x05F2, 0x0621, 0x063A, 0x0641, 0x064A,
    0x0671, 0x06B7, 0x06BA, 0x06BE, 0x06C0, 0x06CE, 0x06D0, 0x06D3, 0x06D5, 0x06D5,
    0x06E5, 0x06E6, 0x0905, 0x0939, 0x093D, 0x093D, 0x0958, 0x0961, 0x0985, 0x098C,
    0x098F, 0x0990, 0x0993, 0x09A8, 0x09AA, 0x09B0, 0x09B2, 0x09B2, 0x09B6, 0x09B9,
    0x09DC, 0x09DD, 0x09DF, 0x09E1, 0x09F0, 0x09F1, 0x0A05, 0x0A0A, 0x0A0F, 0x0A10,
    0x0A13, 0x0A28, 0x0A2A, 0x0A30, 0x0A32, 0x0A33, 0x0A35, 0x0A36, 0x0A38, 0x0A39,
    0x0A59, 0x0A5C, 0x0A5E, 0x0A5E, 0x0A72, 0x0A74, 0x0A85, 0x0A8B, 0x0A8D, 0x0A8D,
    0x0A8F, 0x0A91, 0x0A93, 0x0AA8, 0x0AAA, 0x0AB0, 0x0AB2, 0x0AB3, 0x0AB5, 0x0AB9,
    0x0ABD, 0x0ABD, 0x0AE0, 0x0AE0, 0x0B05, 0x0B0C, 0x0B0F, 0x0B10, 0x0B13, 0x0B28,
    0x0B2A, 0x0B30, 0x0B32, 0x0B33, 0x0B36, 0x0B39, 0x0B3D, 0x0B3D, 0x0B5C, 0x0B5D,
    0x0B5F, 0x0B61, 0x0B85, 0x0B8A, 0x0B8E, 0x0B90, 0x0B92, 0x0B95, 0x0B99, 0x0B9A,
    0x0B9C, 0x0B9C, 0x0B9E, 0x0B9F, 0x0BA3, 0x0BA4, 0x0BA8, 0x0BAA, 0x0BAE, 0x0BB5,
    0x0BB7, 0x0BB9, 0x0C05, 0x0C0C, 0x0C0E, 0x0C10, 0x0C12, 0x0C28, 0x0C2A, 0x0C33,
    0x0C35, 0x0C39, 0x0C60, 0x0C61, 0x0C85, 0x0C8C, 0x0C8E, 0x0C90, 0x0C92, 0x0CA8,
    0x0CAA, 0x0CB3, 0x0CB5, 0x0CB9, 0x0CDE, 0x0CDE, 0x0CE0, 0x0CE1, 0x0D05, 0x0D0C,
    0x0D0E, 0x0D10, 0x0D12, 0x0D28, 0x0D2A, 0x0D39, 0x0D60, 0x0D61, 0x0E01, 0x0E2E,
    0x0E30, 0x0E30, 0x0E32, 0x0E33, 0x0E40, 0x0E45, 0x0E81, 0x0E82, 0x0E84, 0x0E84,
    0x0E87, 0x0E88, 0x0E8A, 0x0E8A, 0x0E8D, 0x0E8D, 0x0E94, 0x0E97, 0x0E99, 0x0E9F,
    0x0EA1, 0x0EA3, 0x0EA5, 0x0EA5, 0x0EA7, 0x0EA7, 0x0EAA, 0x0EAB, 0x0EAD, 0x0EAE,
    0x0EB0, 0x0EB0, 0x0EB2, 0x0EB3, 0x0EBD, 0x0EBD, 0x0EC0, 0x0EC4, 0x0F40, 0x0F47,
    0x0F49, 0x0F69, 0x10A0, 0x10C5, 0x10D0, 0x10F6, 0x1100, 0x1100, 0x1102, 0x1103,
    0x1105, 0x1107, 0x1109, 0x1109, 0x110B, 0x110C, 0x110E, 0x1112, 0x113C, 0x113C,
    0x113E, 0x113E, 0x1140, 0x1140, 0x114C, 0x114C, 0x114E, 0x114E, 0x1150, 0x1150,
    0x1154, 0x1155, 0x1159, 0x1159, 0x115F, 0x1161, 0x1163, 0x1163, 0x1165, 0x1165,
    0x1167, 0x1167, 0x1169, 0x1169, 0x116D, 0x116E, 0x1172, 0x1173, 0x1175, 0x1175,
    0x119E, 0x119E, 0x11A8, 0x11A8, 0x11AB, 0x11AB, 0x11AE, 0x11AF, 0x11B7, 0x11B8,
    0x11BA, 0x11BA, 0x11BC, 0x11C2, 0x11EB, 0x11EB, 0x11F0, 0x11F0, 0x11F9, 0x11F9,
    0x1E00, 0x1E9B, 0x1EA0, 0x1EF9, 0x1F00, 0x1F15, 0x1F18, 0x1F1D, 0x1F20, 0x1F45,
    0x1F48, 0x1F4D, 0x1F50, 0x1F57, 0x1F59, 0x1F59, 0x1F5B, 0x1F5B, 0x1F5D, 0x1F5D,
    0x1F5F, 0x1F7D, 0x1F80, 0x1FB4, 0x1FB6, 0x1FBC, 0x1FBE, 0x1FBE, 0x1FC2, 0x1FC4,
    0x1FC6, 0x1FCC, 0x1FD0, 0x1FD3, 0x1FD6, 0x1FDB, 0x1FE0, 0x1FEC, 0x1FF2, 0x1FF4,
    0x1FF6, 0x1FFC, 0x2126, 0x2126, 0x212A, 0x212B, 0x212E, 0x212E, 0x2180, 0x2182,
    0x3007, 0x3007, 0x3021, 0x3029, 0x3041, 0x3094, 0x30A1, 0x30FA, 0x3105, 0x312C,
    0x4E00, 0x9FA5, 0xAC00, 0xD7A3), ncol = 2, byrow = TRUE)

# 'Digit | CombiningChar | Extender', minus the ASCII digits
# is_name_char() tests directly. Same shape as xml_letters
xml_other_name_chars <- matrix(c(
    0x00B7, 0x00B7, 0x02D0, 0x02D1, 0x0300, 0x0345, 0x0360, 0x0361, 0x0387, 0x0387,
    0x0483, 0x0486, 0x0591, 0x05A1, 0x05A3, 0x05B9, 0x05BB, 0x05BD, 0x05BF, 0x05BF,
    0x05C1, 0x05C2, 0x05C4, 0x05C4, 0x0640, 0x0640, 0x064B, 0x0652, 0x0660, 0x0669,
    0x0670, 0x0670, 0x06D6, 0x06E4, 0x06E7, 0x06E8, 0x06EA, 0x06ED, 0x06F0, 0x06F9,
    0x0901, 0x0903, 0x093C, 0x093C, 0x093E, 0x094D, 0x0951, 0x0954, 0x0962, 0x0963,
    0x0966, 0x096F, 0x0981, 0x0983, 0x09BC, 0x09BC, 0x09BE, 0x09C4, 0x09C7, 0x09C8,
    0x09CB, 0x09CD, 0x09D7, 0x09D7, 0x09E2, 0x09E3, 0x09E6, 0x09EF, 0x0A02, 0x0A02,
    0x0A3C, 0x0A3C, 0x0A3E, 0x0A42, 0x0A47, 0x0A48, 0x0A4B, 0x0A4D, 0x0A66, 0x0A71,
    0x0A81, 0x0A83, 0x0ABC, 0x0ABC, 0x0ABE, 0x0AC5, 0x0AC7, 0x0AC9, 0x0ACB, 0x0ACD,
    0x0AE6, 0x0AEF, 0x0B01, 0x0B03, 0x0B3C, 0x0B3C, 0x0B3E, 0x0B43, 0x0B47, 0x0B48,
    0x0B4B, 0x0B4D, 0x0B56, 0x0B57, 0x0B66, 0x0B6F, 0x0B82, 0x0B83, 0x0BBE, 0x0BC2,
    0x0BC6, 0x0BC8, 0x0BCA, 0x0BCD, 0x0BD7, 0x0BD7, 0x0BE7, 0x0BEF, 0x0C01, 0x0C03,
    0x0C3E, 0x0C44, 0x0C46, 0x0C48, 0x0C4A, 0x0C4D, 0x0C55, 0x0C56, 0x0C66, 0x0C6F,
    0x0C82, 0x0C83, 0x0CBE, 0x0CC4, 0x0CC6, 0x0CC8, 0x0CCA, 0x0CCD, 0x0CD5, 0x0CD6,
    0x0CE6, 0x0CEF, 0x0D02, 0x0D03, 0x0D3E, 0x0D43, 0x0D46, 0x0D48, 0x0D4A, 0x0D4D,
    0x0D57, 0x0D57, 0x0D66, 0x0D6F, 0x0E31, 0x0E31, 0x0E34, 0x0E3A, 0x0E46, 0x0E4E,
    0x0E50, 0x0E59, 0x0EB1, 0x0EB1, 0x0EB4, 0x0EB9, 0x0EBB, 0x0EBC, 0x0EC6, 0x0EC6,
    0x0EC8, 0x0ECD, 0x0ED0, 0x0ED9, 0x0F18, 0x0F19, 0x0F20, 0x0F29, 0x0F35, 0x0F35,
    0x0F37, 0x0F37, 0x0F39, 0x0F39, 0x0F3E, 0x0F3F, 0x0F71, 0x0F84, 0x0F86, 0x0F8B,
    0x0F90, 0x0F95, 0x0F97, 0x0F97, 0x0F99, 0x0FAD, 0x0FB1, 0x0FB7, 0x0FB9, 0x0FB9,
    0x20D0, 0x20DC, 0x20E1, 0x20E1, 0x3005, 0x3005, 0x302A, 0x302F, 0x3031, 0x3035,
    0x3099, 0x309A, 0x309D, 0x309E, 0x30FC, 0x30FE), ncol = 2, byrow = TRUE)

# Whether each code point in 'cp' falls in one of the (first, last)
# ranges of 'ranges'
in_ranges <- function(cp, ranges) {
    i <- findInterval(cp, ranges[, 1])
    found <- i > 0
    found[found] <- cp[found] <= ranges[i[found], 2]
    found
}

is_name_start_char <- function(cp) {
    (cp >= 0x41 & cp <= 0x5A) | (cp >= 0x61 & cp <= 0x7A) | cp == 0x5F |
        in_ranges(cp, xml_letters)
}

is_name_char <- function(cp) {
    is_name_start_char(cp) | (cp >= 0x30 & cp <= 0x39) |
        cp == 0x2D | cp == 0x2E | in_ranges(cp, xml_other_name_chars)
}

# Whether 'name' is an XML NCName, i.e. a Name (Appendix B above) with
# no colon in it
is_ncname <- function(name) {
    cp <- suppressWarnings(utf8ToInt(enc2utf8(name)))
    # A name that is not valid UTF-8 (utf8ToInt() gives NA) is no more
    # writable into an XPath expression than one made of the wrong
    # characters
    if (!length(cp) || anyNA(cp))
        return(FALSE)
    is_name_start_char(cp[1]) && all(is_name_char(cp))
}