[Bug 56399] cmd.exe's %~s modifier (short DOS path) expands to mixed short/long format

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=56399

--- Comment #3 from [e-mail] ---
The problematic code is in:
wine/programs/cmd/batch.c, function WCMD_HandleTildeModifiers @ line 546

/* 4. Handle 's' : Use short paths (File doesn't have to exist) */
if (wmemchr(firstModifier, 's', modifierLen) != NULL) {
    if (finaloutput[0] != 0x00) lstrcatW(finaloutput, L" ");

/* Convert fullfilename's path to a short path - Save filename away as
        only path is valid, name may not exist which causes GetShortPathName
        to fail if it is provided                                           */
    if (filepart) {
    lstrcpyW(thisoutput, filepart);
    *filepart = 0x00;
    GetShortPathNameW(fullfilename, fullfilename, ARRAY_SIZE(fullfilename));
    lstrcatW(fullfilename, thisoutput);
    }
}

The first question is, why does the conversion always take place without the
file at the end of the path?
This is always wrong for file names with more than 8 characters.

The second question is why a directory at the end of the path is recognized as
a file?

To solve the first question, my proposal would be the following change:

/* 4. Handle 's' : Use short paths (File doesn't have to exist) */
if (wmemchr(firstModifier, 's', modifierLen) != NULL) {
    if (finaloutput[0] != 0x00) lstrcatW(finaloutput, L" ");

if (exists) {
        GetShortPathNameW(fullfilename, fullfilename,
                          ARRAY_SIZE(fullfilename));
    } else {
        WIN32_FILE_ATTRIBUTE_DATA dirInfo;
        int i_end = lstrlenW(fullfilename);
        int i_cut = i_end;
        i = i_end;
        while (i-- > 0) {
            /* Cut the last element of the path chain until the path resolves
               to a existing directory */
            if (fullfilename[i] == L'\' || fullfilename[i] == L'/') {
                /* Undo the previous cut */
                if (i_cut < i_end) fullfilename[i_cut] = L'\';
                fullfilename[i] = 0x00;
                i_cut = i;
                if (GetFileAttributesExW(fullfilename, GetFileExInfoStandard,
                                         &dirInfo) != FALSE) {
                    /* Keep the non-existing end of the path chain and append
                       it to the new short path */
                    lstrcpyW(&thisoutput[1], &fullfilename[i_cut + 1]);
                    thisoutput[0] = L'\';
                    GetShortPathNameW(fullfilename, fullfilename,
                                      ARRAY_SIZE(fullfilename));
                    lstrcatW(fullfilename, thisoutput);
                    break;
                }
            }
        }
    }
}

Unfortunately I can't test this at the moment so I would be happy if someone
could perhaps take this on.