fileName isn't used when wildcardPattern is null, so we should avoid the call (which copies and allocates memory) unless we'll actually use the value.

Actually, shouldn't fileName also be used when there are no wildcards? Currently

if (filePath.IndexOf(pattern, StringComparison.OrdinalIgnoreCase) >= 0)

is searching the whole path for a match. If it is desirable to only target the file name when performing the wildcard match, shouldn't it also be appropriate here? (Actually, given that an exact match is expected — that's how GetFiles would work in the non-UNIX case for a non-wildcard pattern, if I am not mistaken — shouldn't the test be against fileName.Equals(pattern, StringComparison.OrdinalIgnoreCase) instead of using IndexOf?)

(An unrelated minor issue I believe exists with the logic of GetFiles is using break instead of continue when a non-wildcard match is found. This might limit the matches in the (rare) case in which a file name equals a wildcard search pattern, e.g. foo?, though I haven't tested how GetFileswould behave in that scenario, and it might be nitpicking if the expected directory and file names are curated.

Also, sorry for butting in, but since I wasn't sure enough about my observations I didn't want to open an issue, so I didn't know a better way to proceed.)

@gonhidi - thanks for the extra scrutiny - it is definitely appreciated.

It does seem like there should be consistency between wildcards and non-wildcards. Feel free to open an issue.