      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259

    /// A few elementary UTF-8 encoding and decoding functions used by the matching
    /// engines.
    ///
    /// In an ideal world, the matching engines operate on `&str` and we can just
    /// lean on the standard library for all our UTF-8 needs. However, to support
    /// byte based regexes (that can match on arbitrary bytes which may contain
    /// UTF-8), we need to be capable of searching and decoding UTF-8 on a `&[u8]`.
    /// The standard library doesn't really recognize this use case, so we have
    /// to build it out ourselves.
    ///
    /// Should this be factored out into a separate crate? It seems independently
    /// useful. There are other crates that already exist (e.g., `utf-8`) that have
    /// overlapping use cases. Not sure what to do.

    use std::char;

    const TAG_CONT: u8 = 0b1000_0000;
    const TAG_TWO: u8 = 0b1100_0000;
    const TAG_THREE: u8 = 0b1110_0000;
    const TAG_FOUR: u8 = 0b1111_0000;

    /// Returns the smallest possible index of the next valid UTF-8 sequence
    /// starting after `i`.
    pub fn next_utf8(text: &[u8], i: usize) -> usize {
        let b = match text.get(i) {
            None => return i + 1,
            Some(&b) => b,
        };
        let inc = if b <= 0x7F {
            1
        } else if b <= 0b110_11111 {
            2
        } else if b <= 0b1110_1111 {
            3
        } else {
            4
        };
        i + inc
    }

    /// Decode a single UTF-8 sequence into a single Unicode codepoint from `src`.
    ///
    /// If no valid UTF-8 sequence could be found, then `None` is returned.
    /// Otherwise, the decoded codepoint and the number of bytes read is returned.
    /// The number of bytes read (for a valid UTF-8 sequence) is guaranteed to be
    /// 1, 2, 3 or 4.
    ///
    /// Note that a UTF-8 sequence is invalid if it is incorrect UTF-8, encodes a
    /// codepoint that is out of range (surrogate codepoints are out of range) or
    /// is not the shortest possible UTF-8 sequence for that codepoint.
    #[inline]
    pub fn decode_utf8(src: &[u8]) -> Option<(char, usize)> {
        let b0 = match src.get(0) {
            None => return None,
            Some(&b) if b <= 0x7F => return Some((b as char, 1)),
            Some(&b) => b,
        };
        match b0 {
            0b110_00000 ..= 0b110_11111 => {
                if src.len() < 2 {
                    return None;
                }
                let b1 = src[1];
                if 0b11_000000 & b1 != TAG_CONT {
                    return None;
                }
                let cp = ((b0 & !TAG_TWO) as u32) << 6
                         | ((b1 & !TAG_CONT) as u32);
                match cp {
                    0x80 ..= 0x7FF => char::from_u32(cp).map(|cp| (cp, 2)),
                    _ => None,
                }
            }
            0b1110_0000 ..= 0b1110_1111 => {
                if src.len() < 3 {
                    return None;
                }
                let (b1, b2) = (src[1], src[2]);
                if 0b11_000000 & b1 != TAG_CONT {
                    return None;
                }
                if 0b11_000000 & b2 != TAG_CONT {
                    return None;
                }
                let cp = ((b0 & !TAG_THREE) as u32) << 12
                         | ((b1 & !TAG_CONT) as u32) << 6
                         | ((b2 & !TAG_CONT) as u32);
                match cp {
                    // char::from_u32 will disallow surrogate codepoints.
                    0x800 ..= 0xFFFF => char::from_u32(cp).map(|cp| (cp, 3)),
                    _ => None,
                }
            }
            0b11110_000 ..= 0b11110_111 => {
                if src.len() < 4 {
                    return None;
                }
                let (b1, b2, b3) = (src[1], src[2], src[3]);
                if 0b11_000000 & b1 != TAG_CONT {
                    return None;
                }
                if 0b11_000000 & b2 != TAG_CONT {
                    return None;
                }
                if 0b11_000000 & b3 != TAG_CONT {
                    return None;
                }
                let cp = ((b0 & !TAG_FOUR) as u32) << 18
                         | ((b1 & !TAG_CONT) as u32) << 12
                         | ((b2 & !TAG_CONT) as u32) << 6
                         | ((b3 & !TAG_CONT) as u32);
                match cp {
                    0x10000 ..= 0x10FFFF => char::from_u32(cp).map(|cp| (cp, 4)),
                    _ => None,
                }
            }
            _ => None,
        }
    }

    /// Like `decode_utf8`, but decodes the last UTF-8 sequence in `src` instead
    /// of the first.
    pub fn decode_last_utf8(src: &[u8]) -> Option<(char, usize)> {
        if src.is_empty() {
            return None;
        }
        let mut start = src.len() - 1;
        if src[start] <= 0x7F {
            return Some((src[start] as char, 1));
        }
        while start > src.len().saturating_sub(4) {
            start -= 1;
            if is_start_byte(src[start]) {
                break;
            }
        }
        match decode_utf8(&src[start..]) {
            None => None,
            Some((_, n)) if n < src.len() - start => None,
            Some((cp, n)) => Some((cp, n)),
        }
    }

    fn is_start_byte(b: u8) -> bool {
        b & 0b11_000000 != 0b1_0000000
    }

    #[cfg(test)]
    mod tests {
        use std::str;

        use quickcheck::quickcheck;

        use super::{
            TAG_CONT, TAG_TWO, TAG_THREE, TAG_FOUR,
            decode_utf8, decode_last_utf8,
        };

        #[test]
        fn prop_roundtrip() {
            fn p(given_cp: char) -> bool {
                let mut tmp = [0; 4];
                let encoded_len = given_cp.encode_utf8(&mut tmp).len();
                let (got_cp, got_len) = decode_utf8(&tmp[..encoded_len]).unwrap();
                encoded_len == got_len && given_cp == got_cp
            }
            quickcheck(p as fn(char) -> bool)
        }

        #[test]
        fn prop_roundtrip_last() {
            fn p(given_cp: char) -> bool {
                let mut tmp = [0; 4];
                let encoded_len = given_cp.encode_utf8(&mut tmp).len();
                let (got_cp, got_len) =
                    decode_last_utf8(&tmp[..encoded_len]).unwrap();
                encoded_len == got_len && given_cp == got_cp
            }
            quickcheck(p as fn(char) -> bool)
        }

        #[test]
        fn prop_encode_matches_std() {
            fn p(cp: char) -> bool {
                let mut got = [0; 4];
                let n = cp.encode_utf8(&mut got).len();
                let expected = cp.to_string();
                &got[..n] == expected.as_bytes()
            }
            quickcheck(p as fn(char) -> bool)
        }

        #[test]
        fn prop_decode_matches_std() {
            fn p(given_cp: char) -> bool {
                let mut tmp = [0; 4];
                let n = given_cp.encode_utf8(&mut tmp).len();
                let (got_cp, _) = decode_utf8(&tmp[..n]).unwrap();
                let expected_cp =
                    str::from_utf8(&tmp[..n]).unwrap().chars().next().unwrap();
                got_cp == expected_cp
            }
            quickcheck(p as fn(char) -> bool)
        }

        #[test]
        fn prop_decode_last_matches_std() {
            fn p(given_cp: char) -> bool {
                let mut tmp = [0; 4];
                let n = given_cp.encode_utf8(&mut tmp).len();
                let (got_cp, _) = decode_last_utf8(&tmp[..n]).unwrap();
                let expected_cp =
                    str::from_utf8(&tmp[..n]).unwrap()
                        .chars().rev().next().unwrap();
                got_cp == expected_cp
            }
            quickcheck(p as fn(char) -> bool)
        }

        #[test]
        fn reject_invalid() {
            // Invalid start byte
            assert_eq!(decode_utf8(&[0xFF]), None);
            // Surrogate pair
            assert_eq!(decode_utf8(&[0xED, 0xA0, 0x81]), None);
            // Invalid continuation byte.
            assert_eq!(decode_utf8(&[0xD4, 0xC2]), None);
            // Bad lengths
            assert_eq!(decode_utf8(&[0xC3]), None); // 2 bytes
            assert_eq!(decode_utf8(&[0xEF, 0xBF]), None); // 3 bytes
            assert_eq!(decode_utf8(&[0xF4, 0x8F, 0xBF]), None); // 4 bytes
            // Not a minimal UTF-8 sequence
            assert_eq!(decode_utf8(&[TAG_TWO, TAG_CONT | b'a']), None);
            assert_eq!(decode_utf8(&[TAG_THREE, TAG_CONT, TAG_CONT | b'a']), None);
            assert_eq!(decode_utf8(&[
                TAG_FOUR, TAG_CONT, TAG_CONT, TAG_CONT | b'a',
            ]), None);
        }

        #[test]
        fn reject_invalid_last() {
            // Invalid start byte
            assert_eq!(decode_last_utf8(&[0xFF]), None);
            // Surrogate pair
            assert_eq!(decode_last_utf8(&[0xED, 0xA0, 0x81]), None);
            // Bad lengths
            assert_eq!(decode_last_utf8(&[0xC3]), None); // 2 bytes
            assert_eq!(decode_last_utf8(&[0xEF, 0xBF]), None); // 3 bytes
            assert_eq!(decode_last_utf8(&[0xF4, 0x8F, 0xBF]), None); // 4 bytes
            // Not a minimal UTF-8 sequence
            assert_eq!(decode_last_utf8(&[TAG_TWO, TAG_CONT | b'a']), None);
            assert_eq!(decode_last_utf8(&[
                TAG_THREE, TAG_CONT, TAG_CONT | b'a',
            ]), None);
            assert_eq!(decode_last_utf8(&[
                TAG_FOUR, TAG_CONT, TAG_CONT, TAG_CONT | b'a',
            ]), None);
        }
    }

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g., `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g., `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g., `str,u8` or `String,struct:Vec,test`)