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Fix find_width_of_character_at_span bounds check

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Commit 0bd96671f0 added bounds checking of our current target byte
position to prevent infinite loops. Unfortunately it was comparing the
file-relative `target` versus the global relative `file_start_pos` and
`file_end_pos`.

The result is failing to detect multibyte characters unless their
file-relative offset fit within their global offset. This causes other
parts of the compiler to generate spans pointing to the middle of a
multibyte character which will ultimately panic in
`bytepos_to_file_charpos`.

Fix by comparing the `target` to the total file size when moving forward
and doing checked subtraction when moving backwards. This should
preserve the intent of the bounds check while removing the offset
confusion.

Fixes #48508
This commit is contained in:
Ryan Cumming 2018-02-25 11:41:08 +11:00
parent 6070d3e47e
commit d27fac618d
1 changed files with 11 additions and 8 deletions
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19
src/libsyntax/codemap.rs
View file

@ -705,17 +705,20 @@ impl CodeMap {
};
debug!("find_width_of_character_at_span: snippet=`{:?}`", snippet);
let file_start_pos = local_begin.fm.start_pos.to_usize();
let file_end_pos = local_begin.fm.end_pos.to_usize();
debug!("find_width_of_character_at_span: file_start_pos=`{:?}` file_end_pos=`{:?}`",
file_start_pos, file_end_pos);
let mut target = if forwards { end_index + 1 } else { end_index - 1 };
debug!("find_width_of_character_at_span: initial target=`{:?}`", target);
while !snippet.is_char_boundary(target - start_index)
&& target >= file_start_pos && target <= file_end_pos {
target = if forwards { target + 1 } else { target - 1 };
while !snippet.is_char_boundary(target - start_index) && target < source_len {
target = if forwards {
target + 1
} else {
match target.checked_sub(1) {
Some(target) => target,
None => {
break;
}
}
};
debug!("find_width_of_character_at_span: target=`{:?}`", target);
}
debug!("find_width_of_character_at_span: final target=`{:?}`", target);