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Auto merge of #32064 - bluss:str-slice-panic, r=alexcrichton

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Fix panic on string slicing error to truncate the string

The string may be arbitrarily long, but we want to limit the panic
message to a reasonable length. Truncate the string if it is too long
(simply to char boundary).

Also add details to the start <= end message. I think it's ok to flesh
out the code here, since it's in a cold function.

Fixes #32063
This commit is contained in:
bors 2016-03-07 02:28:09 +00:00
commit 6eb81a1f3b
2 changed files with 41 additions and 3 deletions
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24
src/libcore/str/mod.rs
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@ -1645,12 +1645,30 @@ pub trait StrExt {
fn parse<T: FromStr>(&self) -> Result<T, T::Err>;
}
// truncate `&str` to length at most equal to `max`
// return `true` if it were truncated, and the new str.
fn truncate_to_char_boundary(s: &str, mut max: usize) -> (bool, &str) {
if max >= s.len() {
(false, s)
} else {
while !s.is_char_boundary(max) {
max -= 1;
}
(true, &s[..max])
}
}
#[inline(never)]
#[cold]
fn slice_error_fail(s: &str, begin: usize, end: usize) -> ! {
assert!(begin <= end);
panic!("index {} and/or {} in `{}` do not lie on character boundary",
begin, end, s);
const MAX_DISPLAY_LENGTH: usize = 256;
let (truncated, s) = truncate_to_char_boundary(s, MAX_DISPLAY_LENGTH);
let ellipsis = if truncated { "[...]" } else { "" };
assert!(begin <= end, "begin <= end ({} <= {}) when slicing `{}`{}",
begin, end, s, ellipsis);
panic!("index {} and/or {} in `{}`{} do not lie on character boundary",
begin, end, s, ellipsis);
}
#[stable(feature = "core", since = "1.6.0")]