Function filevercmp

pub(crate) fn filevercmp(a: &[u8], b: &[u8]) -> Ordering

Compare strings A and B as file names containing version numbers, and return an integer that is negative, zero, or positive depending on whether A compares less than, equal to, or greater than B.

Use the following version sort algorithm:

1. Compare the strings’ maximal-length non-digit prefixes lexically. If there is a difference return that difference. Otherwise discard the prefixes and continue with the next step.

2. Compare the strings’ maximal-length digit prefixes, using numeric comparison of the numbers represented by each prefix. (Treat an empty prefix as zero; this can happen only at string end.) If there is a difference, return that difference. Otherwise discard the prefixes and continue with the next step.

3. If both strings are empty, return 0. Otherwise continue with step 1.

In version sort, lexical comparison is left to right, byte by byte, using the byte’s numeric value (0-255), except that:

1. ASCII letters sort before other bytes.
2. A tilde sorts before anything, even an empty string.

In addition to the version sort rules, the following strings have special priority and sort before all other strings (listed in order):

1. The empty string.
2. “.”.
3. “..”.
4. Strings starting with “.” sort before other strings.

Before comparing two strings where both begin with non-“.”, or where both begin with “.” but neither is “.” or “..”, suffixes matching the C-locale extended regular expression (.[A-Za-z~][A-Za-z0-9~])$ are removed and the strings compared without them, using version sort without special priority; if they do not compare equal, this comparison result is used and the suffixes are effectively ignored. Otherwise, the entire strings are compared using version sort. When removing a suffix from a nonempty string, remove the maximal-length suffix such that the remaining string is nonempty.

This function is intended to be a replacement for strverscmp.