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//! Detects a string literal, like `"Hello \"Rust\""` or `r#"Hello "Rust""#`.
/// Detects a string literal, like `"Hello \"Rust\""` or `r#"Hello "Rust""#`.
///
/// @TODO `b` prefix, eg `b"Just the bytes"`
/// @TODO `br` prefix, eg `br#"Just "the" bytes"#`
///
/// ### Arguments
/// * `orig` The original Rust code, assumed to conform to the 2018 edition
/// * `pos` The character position in `orig` to look at
///
/// ### Returns
/// If `pos` begins a valid looking string literal, `detect_string()` returns
/// the character position after the closing single quote (or hash).
/// Otherwise, `detect_string()` just returns the `pos` argument.
pub fn detect_string(orig: &str, pos: usize) -> usize {
// If the current char is the last in `orig`, it does not begin a string.
let len = orig.len();
if len < pos + 1 { return pos }
// If the current char is:
match get_aot(orig, pos) {
// A double quote, `pos` could begin a regular string.
"\"" => detect_regular_string(orig, pos, len),
// A lowercase "r", `pos` could begin a raw string.
"r" => detect_raw_string(orig, pos, len),
// Anything else, `pos` does not begin a string.
_ => pos,
}
}
// Returns the ascii character at a position, or tilde if invalid or non-ascii.
fn get_aot(orig: &str, p: usize) -> &str { orig.get(p..p+1).unwrap_or("~") }
fn detect_regular_string(orig: &str, pos: usize, len: usize) -> usize {
// Slightly hacky way to to skip forward while looping.
let mut i = pos + 1;
// Step through each char, from `pos` to the end of the original input code.
while i < len {
// Get this character, even if it’s non-ascii.
let mut j = i + 1;
while !orig.is_char_boundary(j) { j += 1 }
let c = &orig[i..j];
// If this char is a backslash:
if c == "\\" {
// If the backlash ends the input code, this is not a string.
if j == len { return pos }
// Ignore the next character, even if it’s non-ascii.
// Treat "\€" as a string Lexeme, even though it’s invalid code.
j += 1;
while !orig.is_char_boundary(j) { j += 1 }
// If this char is a double quote:
} else if c == "\"" {
// Advance to the end of the double quote.
return j
}
// Step forward, ready for the next iteration.
i = j;
}
// The closing double quote was not found, so this is not a string.
pos
}
// doc.rust-lang.org/reference/tokens.html#raw-string-literals
fn detect_raw_string(orig: &str, pos: usize, len: usize) -> usize {
// If there are less than two chars after the "r", it cannot begin a string.
if len < pos + 3 { return pos }
// Slightly hacky way to to skip forward while looping.
let mut i = pos + 1;
// Keep track of the number of leading hashes.
let mut hashes = 0;
// Keep track of finding the opening and closing double quotes.
let mut found_opening_dq = false;
let mut found_closing_dq = false;
// Step through each char, from `pos` to the end of the original input code.
// `len-1` saves a nanosecond or two, but also prevents `orig[i..i+1]` from
// panicking at the end of the input.
while i < len {
// Get this character, even if it’s non-ascii.
let mut j = i + 1;
while !orig.is_char_boundary(j) { j += 1 }
let c = &orig[i..j];
// If we have not found the opening double quote yet:
if ! found_opening_dq {
// If this is the opening double quote, note that it’s been found.
if c == "\"" {
found_opening_dq = true
// Otherwise, if this is a leading hash, increment the tally.
} else if c == "#" {
hashes += 1
// Anything else is not valid for the start of a raw string.
} else {
return pos
}
// Otherwise, if we have already found the closing double quote:
} else if found_closing_dq {
// If we are not expecting any more hashes:
if hashes == 0 {
// Valid raw string, advance to the end of the double quote.
return j
// Otherwise, if this is a trailing hash, decrement the tally.
} else if c == "#" {
hashes -= 1;
// If we are not expecting any more hashes:
if hashes == 0 {
// Valid raw string, advance to the end of the double quote.
return j
}
// Anything else is not valid for the end of a raw string.
} else {
return pos
}
// Otherwise we are inside the main part of the string:
} else {
// If this char is a backslash:
if c == "\\" {
// If the backlash ends the input code, this is not a string.
if j == len { return pos }
// Ignore the next character, even if it’s non-ascii.
// Treat "\€" as a string Lexeme, even though it’s invalid code.
j += 1;
while !orig.is_char_boundary(j) { j += 1 }
// If this char is a double quote:
} else if c == "\"" {
// Note that the closing double quote has been found.
found_closing_dq = true;
// If we are not expecting any more hashes:
if hashes == 0 {
// Valid raw string, advance to the end of the double quote.
return j
}
}
}
// Step forward, ready for the next iteration.
i = j;
}
// Reached the end of the `orig` input string. Any leading hashes should have
// been balanced by trailing hashes.
if found_closing_dq && hashes == 0 { i } else { pos }
}
#[cfg(test)]
mod tests {
use super::detect_string as detect;
#[test]
fn detect_string_correct() {
// Regular.
let orig = "abc\"ok\"xyz";
assert_eq!(detect(orig, 2), 2); // c"ok
assert_eq!(detect(orig, 3), 7); // "ok" advance four places
assert_eq!(detect(orig, 4), 4); // ok"x
// Raw.
assert_eq!(detect("-r\"ok\"-", 1), 6);
assert_eq!(detect("r#\"ok\"#", 0), 7);
assert_eq!(detect("abcr###\"ok\"###xyz", 3), 14);
assert_eq!(detect("abcr###\"ok\"####xyz", 3), 14);
// Byte.
// @TODO
// Byte raw.
// @TODO
// Escapes.
// Escaped double quote.
let orig = "a\"b\\\"c\"d";
assert_eq!(detect(orig, 0), 0); // a"b\"c
assert_eq!(detect(orig, 1), 7); // "b\"c" advance six places
assert_eq!(detect(orig, 2), 2); // b\"c"d
assert_eq!(detect(orig, 3), 3); // \"c"d
assert_eq!(detect(orig, 4), 7); // "c"d no ‘lookbehind’ happens!
// Correct escapes, regular string.
let orig = r#"a"\0\\\\\"\\\n"z"#;
assert_eq!(detect(orig, 0), 0); // a"\0\\\\\"\\\n"
assert_eq!(detect(orig, 1), 15); // "\0\\\\\"\\\n"z
assert_eq!(detect(orig, 2), 2); // \0\\\\\"\\\n"z
assert_eq!(detect(orig, 9), 15); // "\\\n"z no ‘lookbehind’s!
assert_eq!(detect(orig, 14), 14); // "z not a string, has no end
// Correct escapes, raw string.
assert_eq!(detect("r\"\\0\\n\\t\"", 0), 9); // r"\0\n\t"
}
#[test]
fn detect_string_incorrect() {
// Incorrect escapes, regular string.
assert_eq!(detect("\\a\\b\\c", 0), 0); // \a\b\c
// Incorrect escapes, raw string.
assert_eq!(detect("r#\"\\X\\Y\\Z\"#", 0), 11); // r#"\X\Y\Z"#
// Incorrect raw.
assert_eq!(detect("r##X#\" X in leading hashes \"###", 0), 0);
assert_eq!(detect("r###\" X in trailing hashes \"##X#", 0), 0);
assert_eq!(detect("r###\" too few trailing hashes \"##", 0), 0);
assert_eq!(detect("-r###\" no trailing hashes \"-", 1), 1);
// Incorrect byte.
// @TODO
// Incorrect byte raw.
// @TODO
}
#[test]
fn detect_string_will_not_panic() {
// Near the end of the `orig` input code.
assert_eq!(detect("", 0), 0); // empty string
assert_eq!(detect("\"", 0), 0); // "
assert_eq!(detect("\"a", 0), 0); // "a
assert_eq!(detect("\"\\", 0), 0); // "\
assert_eq!(detect("\"\\n", 0), 0); // "\n
assert_eq!(detect("\"\\z", 0), 0); // "\z
assert_eq!(detect("\"\\z\\", 0), 0); // "\z\
assert_eq!(detect("\"\\z\\\"", 0), 0); // "\z\"
assert_eq!(detect("r", 0), 0); // r
assert_eq!(detect("r\"", 0), 0); // r"
assert_eq!(detect("r\"a", 0), 0); // r"a
assert_eq!(detect("r\"\\", 0), 0); // r"\
assert_eq!(detect("r\"\\n", 0), 0); // r"\n
assert_eq!(detect("r\"\\z", 0), 0); // r"\z
assert_eq!(detect("r\"\\z\\", 0), 0); // r"\z\
assert_eq!(detect("r\"\\z\\\"", 0), 0); // r"\z\"
assert_eq!(detect("r\"\\z\\\"\"", 0), 7); // r"\z\""
assert_eq!(detect("r#", 0), 0); // r#
assert_eq!(detect("r#\"", 0), 0); // r#"
assert_eq!(detect("r#\"a", 0), 0); // r#"a
assert_eq!(detect("r#\"\\", 0), 0); // r#"\
assert_eq!(detect("r#\"\\n", 0), 0); // r#"\n
assert_eq!(detect("r#\"\\z", 0), 0); // r#"\z
assert_eq!(detect("r#\"\\z\\", 0), 0); // r#"\z\
assert_eq!(detect("r#\"\\z\\\"", 0), 0); // r#"\z\"
assert_eq!(detect("r#\"\\z\\\"#", 0), 0); // r#"\z\"#
assert_eq!(detect("r#\"\\z\\\"\"#", 0), 9); // r#"\z\""#
assert_eq!(detect("r##\"\\z\\\"\"#", 0), 0);// r##"\z\""# missing hash
// Invalid `pos`.
assert_eq!(detect("abc", 2), 2); // 2 is before "c", so in range
assert_eq!(detect("abc", 3), 3); // 3 is after "c", so incorrect
assert_eq!(detect("abc", 4), 4); // 4 is out of range
assert_eq!(detect("abc", 100), 100); // 100 is way out of range
// Non-ascii.
assert_eq!(detect("€", 1), 1); // part way through the three eurobytes
assert_eq!(detect("\"€", 0), 0); // non-ascii after "
assert_eq!(detect("\"a€", 0), 0); // non-ascii after "a
assert_eq!(detect("\"\\€", 0), 0); // non-ascii after "\
assert_eq!(detect("\"\\z€", 0), 0); // non-ascii after "\z
assert_eq!(detect("\"\\z\\€", 0), 0); // non-ascii after "\z\
assert_eq!(detect("\"\\z\\\"€", 0), 0); // non-ascii after "\z\"
assert_eq!(detect("\"\\z\\\"\"€", 0), 6); // non-ascii after "\z\""
assert_eq!(detect("\"€\"", 0), 5); // three-byte non-ascii in ""
assert_eq!(detect("\"a€\"", 0), 6); // non-ascii in "a"
assert_eq!(detect("\"\\€\"", 0), 6); // non-ascii in "\"
assert_eq!(detect("\"\\z€\"", 0), 7); // non-ascii in "\z"
assert_eq!(detect("\"\\z\\€\"", 0), 8); // non-ascii in "\z\"
assert_eq!(detect("r\"€", 0), 0); // non-ascii after r"
assert_eq!(detect("r\"a€", 0), 0); // non-ascii after r"a
assert_eq!(detect("r\"\\€", 0), 0); // non-ascii after r"\
assert_eq!(detect("r\"\\z€", 0), 0); // non-ascii after r"\z
assert_eq!(detect("r\"\\z\\€", 0), 0); // non-ascii after r"\z\
assert_eq!(detect("r\"\\z\\\"€", 0), 0); // non-ascii after r"\z\"
assert_eq!(detect("r\"\\z\\\"\"€", 0), 7); // non-ascii after r"\z\""
assert_eq!(detect("r\"€\"", 0), 6); // non-ascii in r""
assert_eq!(detect("r\"a€\"", 0), 7); // non-ascii in r"a"
assert_eq!(detect("r\"\\€\"", 0), 7); // non-ascii in r"\"
assert_eq!(detect("r\"\\z€\"", 0), 8); // non-ascii in r"\z"
assert_eq!(detect("r\"\\z\\€\"", 0), 9); // non-ascii in r"\z\"
assert_eq!(detect("r#\"€", 0), 0); // non-ascii after r#"
assert_eq!(detect("r#\"a€", 0), 0); // non-ascii after r#"a
assert_eq!(detect("r#\"\\€", 0), 0); // non-ascii after r#"\
assert_eq!(detect("r#\"\\z€", 0), 0); // non-ascii after r#"\z
assert_eq!(detect("r#\"\\z\\€", 0), 0); // non-ascii after r#"\z\
assert_eq!(detect("r#\"\\z\\\"€", 0), 0); // non-ascii after r#"\z\"
assert_eq!(detect("r#\"\\z\"€", 0), 0); // non-ascii after r#"\z"
assert_eq!(detect("r#\"€\"", 0), 0); // non-ascii in r#""
assert_eq!(detect("r#\"a€\"", 0), 0); // non-ascii in r#"a"
assert_eq!(detect("r#\"\\€\"", 0), 0); // non-ascii in r#"\"
assert_eq!(detect("r#\"\\z€\"", 0), 0); // non-ascii in r#"\z"
assert_eq!(detect("r#\"\\z\\€\"", 0), 0); // non-ascii in r#"\z\"
assert_eq!(detect("r#\"\\z\\€\\\"\"#", 0), 13); // r#"\z\€\""#
assert_eq!(detect("r##\"\\z\\€\\\"\"#", 0), 0); // missing hash at end
}
}