1use crate::{ParseError, err::{perr, ParseErrorKind::*}, parse::{hex_digit_value, check_suffix}};
2
3
4/// Must start with `\`
5pub(crate) fn unescape<E: Escapee>(input: &str, offset: usize) -> Result<(E, usize), ParseError> {
6 let first = input.as_bytes().get(1)
7 .ok_or(perr(offset, UnterminatedEscape))?;
8 let out = match first {
9 // Quote escapes
10 b'\'' => (E::from_byte(b'\''), 2),
11 b'"' => (E::from_byte(b'"'), 2),
12
13 // Ascii escapes
14 b'n' => (E::from_byte(b'\n'), 2),
15 b'r' => (E::from_byte(b'\r'), 2),
16 b't' => (E::from_byte(b'\t'), 2),
17 b'\\' => (E::from_byte(b'\\'), 2),
18 b'0' => (E::from_byte(b'\0'), 2),
19 b'x' => {
20 let hex_string = input.get(2..4)
21 .ok_or(perr(offset..offset + input.len(), UnterminatedEscape))?
22 .as_bytes();
23 let first = hex_digit_value(hex_string[0])
24 .ok_or(perr(offset..offset + 4, InvalidXEscape))?;
25 let second = hex_digit_value(hex_string[1])
26 .ok_or(perr(offset..offset + 4, InvalidXEscape))?;
27 let value = second + 16 * first;
28
29 if E::SUPPORTS_UNICODE && value > 0x7F {
30 return Err(perr(offset..offset + 4, NonAsciiXEscape));
31 }
32
33 (E::from_byte(value), 4)
34 },
35
36 // Unicode escape
37 b'u' => {
38 if !E::SUPPORTS_UNICODE {
39 return Err(perr(offset..offset + 2, UnicodeEscapeInByteLiteral));
40 }
41
42 if input.as_bytes().get(2) != Some(&b'{') {
43 return Err(perr(offset..offset + 2, UnicodeEscapeWithoutBrace));
44 }
45
46 let closing_pos = input.bytes().position(|b| b == b'}')
47 .ok_or(perr(offset..offset + input.len(), UnterminatedUnicodeEscape))?;
48
49 let inner = &input[3..closing_pos];
50 if inner.as_bytes().first() == Some(&b'_') {
51 return Err(perr(4, InvalidStartOfUnicodeEscape));
52 }
53
54 let mut v: u32 = 0;
55 let mut digit_count = 0;
56 for (i, b) in inner.bytes().enumerate() {
57 if b == b'_'{
58 continue;
59 }
60
61 let digit = hex_digit_value(b)
62 .ok_or(perr(offset + 3 + i, NonHexDigitInUnicodeEscape))?;
63
64 if digit_count == 6 {
65 return Err(perr(offset + 3 + i, TooManyDigitInUnicodeEscape));
66 }
67 digit_count += 1;
68 v = 16 * v + digit as u32;
69 }
70
71 let c = std::char::from_u32(v)
72 .ok_or(perr(offset..closing_pos + 1, InvalidUnicodeEscapeChar))?;
73
74 (E::from_char(c), closing_pos + 1)
75 }
76
77 _ => return Err(perr(offset..offset + 2, UnknownEscape)),
78 };
79
80 Ok(out)
81}
82
83pub(crate) trait Escapee: Into<char> {
84 const SUPPORTS_UNICODE: bool;
85 fn from_byte(b: u8) -> Self;
86 fn from_char(c: char) -> Self;
87}
88
89impl Escapee for u8 {
90 const SUPPORTS_UNICODE: bool = false;
91 fn from_byte(b: u8) -> Self {
92 b
93 }
94 fn from_char(_: char) -> Self {
95 panic!("bug: `<u8 as Escapee>::from_char` was called");
96 }
97}
98
99impl Escapee for char {
100 const SUPPORTS_UNICODE: bool = true;
101 fn from_byte(b: u8) -> Self {
102 b.into()
103 }
104 fn from_char(c: char) -> Self {
105 c
106 }
107}
108
109/// Checks whether the character is skipped after a string continue start
110/// (unescaped backlash followed by `\n`).
111fn is_string_continue_skipable_whitespace(b: u8) -> bool {
112 b == b' ' || b == b'\t' || b == b'\n' || b == b'\r'
113}
114
115/// Unescapes a whole string or byte string.
116#[inline(never)]
117pub(crate) fn unescape_string<E: Escapee>(
118 input: &str,
119 offset: usize,
120) -> Result<(Option<String>, usize), ParseError> {
121 let mut closing_quote_pos = None;
122 let mut i = offset;
123 let mut end_last_escape = offset;
124 let mut value = String::new();
125 while i < input.len() {
126 match input.as_bytes()[i] {
127 // Handle "string continue".
128 b'\\' if input.as_bytes().get(i + 1) == Some(&b'\n') => {
129 value.push_str(&input[end_last_escape..i]);
130
131 // Find the first non-whitespace character.
132 let end_escape = input[i + 2..].bytes()
133 .position(|b| !is_string_continue_skipable_whitespace(b))
134 .ok_or(perr(None, UnterminatedString))?;
135
136 i += 2 + end_escape;
137 end_last_escape = i;
138 }
139 b'\\' => {
140 let (c, len) = unescape::<E>(&input[i..input.len() - 1], i)?;
141 value.push_str(&input[end_last_escape..i]);
142 value.push(c.into());
143 i += len;
144 end_last_escape = i;
145 }
146 b'\r' => {
147 if input.as_bytes().get(i + 1) == Some(&b'\n') {
148 value.push_str(&input[end_last_escape..i]);
149 value.push('\n');
150 i += 2;
151 end_last_escape = i;
152 } else {
153 return Err(perr(i, IsolatedCr))
154 }
155 }
156 b'"' => {
157 closing_quote_pos = Some(i);
158 break;
159 },
160 b if !E::SUPPORTS_UNICODE && !b.is_ascii()
161 => return Err(perr(i, NonAsciiInByteLiteral)),
162 _ => i += 1,
163 }
164 }
165
166 let closing_quote_pos = closing_quote_pos.ok_or(perr(None, UnterminatedString))?;
167
168 let start_suffix = closing_quote_pos + 1;
169 let suffix = &input[start_suffix..];
170 check_suffix(suffix).map_err(|kind| perr(start_suffix, kind))?;
171
172 // `value` is only empty if there was no escape in the input string
173 // (with the special case of the input being empty). This means the
174 // string value basically equals the input, so we store `None`.
175 let value = if value.is_empty() {
176 None
177 } else {
178 // There was an escape in the string, so we need to push the
179 // remaining unescaped part of the string still.
180 value.push_str(&input[end_last_escape..closing_quote_pos]);
181 Some(value)
182 };
183
184 Ok((value, start_suffix))
185}
186
187/// Reads and checks a raw (byte) string literal, converting `\r\n` sequences to
188/// just `\n` sequences. Returns an optional new string (if the input contained
189/// any `\r\n`) and the number of hashes used by the literal.
190#[inline(never)]
191pub(crate) fn scan_raw_string<E: Escapee>(
192 input: &str,
193 offset: usize,
194) -> Result<(Option<String>, u32, usize), ParseError> {
195 // Raw string literal
196 let num_hashes = input[offset..].bytes().position(|b| b != b'#')
197 .ok_or(perr(None, InvalidLiteral))?;
198
199 if input.as_bytes().get(offset + num_hashes) != Some(&b'"') {
200 return Err(perr(None, InvalidLiteral));
201 }
202 let start_inner = offset + num_hashes + 1;
203 let hashes = &input[offset..num_hashes + offset];
204
205 let mut closing_quote_pos = None;
206 let mut i = start_inner;
207 let mut end_last_escape = start_inner;
208 let mut value = String::new();
209 while i < input.len() {
210 let b = input.as_bytes()[i];
211 if b == b'"' && input[i + 1..].starts_with(hashes) {
212 closing_quote_pos = Some(i);
213 break;
214 }
215
216 if b == b'\r' {
217 // Convert `\r\n` into `\n`. This is currently not well documented
218 // in the Rust reference, but is done even for raw strings. That's
219 // because rustc simply converts all line endings when reading
220 // source files.
221 if input.as_bytes().get(i + 1) == Some(&b'\n') {
222 value.push_str(&input[end_last_escape..i]);
223 value.push('\n');
224 i += 2;
225 end_last_escape = i;
226 continue;
227 } else if E::SUPPORTS_UNICODE {
228 // If no \n follows the \r and we are scanning a raw string
229 // (not raw byte string), we error.
230 return Err(perr(i, IsolatedCr))
231 }
232 }
233
234 if !E::SUPPORTS_UNICODE {
235 if !b.is_ascii() {
236 return Err(perr(i, NonAsciiInByteLiteral));
237 }
238 }
239
240 i += 1;
241 }
242
243 let closing_quote_pos = closing_quote_pos.ok_or(perr(None, UnterminatedRawString))?;
244
245 let start_suffix = closing_quote_pos + num_hashes + 1;
246 let suffix = &input[start_suffix..];
247 check_suffix(suffix).map_err(|kind| perr(start_suffix, kind))?;
248
249 // `value` is only empty if there was no \r\n in the input string (with the
250 // special case of the input being empty). This means the string value
251 // equals the input, so we store `None`.
252 let value = if value.is_empty() {
253 None
254 } else {
255 // There was an \r\n in the string, so we need to push the remaining
256 // unescaped part of the string still.
257 value.push_str(&input[end_last_escape..closing_quote_pos]);
258 Some(value)
259 };
260
261 Ok((value, num_hashes as u32, start_suffix))
262}
263