basic_regex::__search error with "$" pattern

[alkino]

Hello,

If we use a pattern like $ or something more complex as *$ but that does not match the string,
__search return false as not found because we don't try the empty string.

The problem is the for loop:

llvm-project/libcxx/include/regex

Line 6165 in ef888bc

for (++__first; __first != __last; ++__first)

An example, is trying to match $ against hello.
We will successively try:

• hello (before the loop)
• ello
• llo
• lo
• o

And nothing else, and so this is not a match.

It seems that having a last run with __match_at_start(__last, __last, __m, __flags, false) (only if match_not_null is not set) fix the problem.