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

use range::Range;
use std::io::{ self, stderr, Write };

use ParseError;

/// When an error happens, reports to standard error and then panics.
pub fn stderr_unwrap<T>(source: &str, res: Result<T, Range<ParseError>>) -> T {
    match res {
        Err(range_err) => {
            ParseErrorHandler::new(source).error(range_err);
            panic!();
        }
        Ok(val) => val,
    }
}

/// Reports error.
pub struct ParseErrorHandler<'a> {
    lines: Vec<(Range, &'a str)>,
}

impl<'a> ParseErrorHandler<'a> {
    /// Creates a new error handler.
    pub fn new(text: &'a str) -> ParseErrorHandler<'a> {
        let mut start = 0;
        let mut lines = vec![];
        for line in text.split('\n') {
            let length = line.len();
            lines.push((Range::new(start, length), line));
            // Lines are separated by '\n'.
            start += length + 1;
        }

        ParseErrorHandler {
            lines: lines,
        }
    }

    /// Writes message.
    pub fn write_msg<W: Write>(
        &mut self,
        w: &mut W,
        range: Range,
        msg: &str
    ) -> Result<(), io::Error> {
        try!(writeln!(w, "{}", msg));
        let mut printed_pointer = false;
        for (i, &(r, text)) in self.lines.iter().enumerate() {
            if let Some(intersect) = range.ends_intersect(&r) {
                if intersect.offset >= r.offset {
                    let j = intersect.offset - r.offset;
                    let s = if j > 75 { j - 50 } else { 0 };
                    let e = ::std::cmp::min(s + 100, r.length);
                    try!(write!(w, "{},{}: ", i + 1, j + 1));
                    for c in text.chars().skip(s).take(e - s) {
                        try!(write!(w, "{}", c));
                    }
                    try!(writeln!(w, ""));
                    if !printed_pointer {
                        try!(write!(w, "{},{}: ", i + 1, j + 1));
                        for c in text.chars().skip(s).take(j - s) {
                            match c {
                                '\t' => {
                                    try!(write!(w, "\t"));
                                }
                                _ => {
                                    try!(write!(w, " "));
                                }
                            }
                        }
                        try!(writeln!(w, "^"));
                        printed_pointer = true;
                    }
                }
            }
        }
        Ok(())
    }

    /// Writes error message.
    pub fn write<W: Write>(
        &mut self,
        w: &mut W,
        range_err: Range<ParseError>
    ) -> Result<(), io::Error> {
        // Gets the first line of error message.
        fn first_line(
            err_handler: &ParseErrorHandler,
            range: Range
        ) -> Option<(usize, Range)> {
            let mut first_line = None;
            for (i, &(r, _)) in err_handler.lines.iter().enumerate() {
                if let Some(intersect) = range.ends_intersect(&r) {
                    first_line = Some((i, intersect));
                    break;
                }
            }
            first_line
        }

        let (range, error) = range_err.decouple();

        try!(writeln!(w, "Error {}", error));
        if let &ParseError::ExpectedTag(_, _) = &error {
            // Improves the error report when forgetting a token at end of
            // a line, for example `;` after an expression.
            if let Some(first_line) = first_line(self, range) {
                let mut prev_line = 0;
                for (i, &(_, text)) in
                    self.lines[..first_line.0].iter().enumerate().rev() {
                    prev_line = i;
                    if !text.chars()
                        .all(|c| { c.is_whitespace() }) { break; }
                }
                for (i, &(_, text)) in
                    self.lines[prev_line .. first_line.0].iter().enumerate() {
                    try!(writeln!(w, "{}: {}",
                        i + prev_line + 1, text));
                }
            }
        }
        let mut printed_pointer = false;
        for (i, &(r, text)) in self.lines.iter().enumerate() {
            if let Some(intersect) = range.ends_intersect(&r) {
                if intersect.offset >= r.offset {
                    let j = intersect.offset - r.offset;
                    let s = if j > 75 { j - 50 } else { 0 };
                    let e = ::std::cmp::min(s + 100, r.length);
                    try!(write!(w, "{},{}: ", i + 1, j + 1));
                    for c in text.chars().skip(s).take(e - s) {
                        try!(write!(w, "{}", c));
                    }
                    try!(writeln!(w, ""));
                    if !printed_pointer {
                        try!(write!(w, "{},{}: ", i + 1, j + 1));
                        for c in text.chars().skip(s).take(j - s) {
                            match c {
                                '\t' => {
                                    try!(write!(w, "\t"));
                                }
                                _ => {
                                    try!(write!(w, " "));
                                }
                            }
                        }
                        try!(writeln!(w, "^"));
                        printed_pointer = true;
                    }
                }
            }
        }
        Ok(())
    }

    /// Prints error message to standard error.
    pub fn error(&mut self, range_err: Range<ParseError>) {
        self.write(&mut stderr(), range_err).unwrap()
    }
}