Fix hasExt() falsely detecting dots in directory path as file extensions - #18540

There is another helper function in CustomFileDialog.cpp that suffers from the exact same logic flaw: replaceExt().

Beyond just code consistency, fixing replaceExt() is actually even more critical. If a user enters a path where a directory contains a dot (e.g., C:\version.1.0\myfile) and changes the file type filter in the dialog, changeExt() calls replaceExt(). Because replaceExt() currently uses an unconstrained find_last_of('.'), it matches the dot inside the directory name (version.1.0) and truncates the entire path right there (C:\version), completely corrupting and destroying the file path before appending the new extension.

To prevent this serious path corruption bug, replaceExt() should be updated using the same directory separator check.

Here is a suggested implementation snippet for replaceExt():

bool replaceExt(wstring& name, const wstring& ext)
{
    if (!name.empty() && !ext.empty())
    {
        // Remove an existing extension from the name only if the dot is after the last path separator
        size_t posNameExt = name.find_last_of(L'.');
        if (posNameExt != wstring::npos)
        {
            size_t lastSlash = name.find_last_of(L"\\/");
            if (lastSlash == wstring::npos || posNameExt > lastSlash)
            {
                name.erase(posNameExt);
            }
        }
        // Append a new extension.
        name += ext;
        return true;
    }
    return false;
}

@vlakoff
Good catch! Thank you for pointing this out.

You are completely right. replaceExt() suffered from the exact same assumption that any dot belongs to a file extension. When the directory path contained a dot (e.g., C:\version.1.0\myfile), replaceExt() truncated the string at .0, completely corrupting the path into C:\version.ext.

I have updated the PR to apply the same path-separator boundary check to replaceExt():

• If a dot exists after the last path separator, it is treated as a file extension and replaced.
• If a dot exists only within directory names (or if there is no dot at all), no existing characters are erased, and the new extension is simply appended.

Test Cases Verified:

• C:\version.1.0\myfile + .txt -> C:\version.1.0\myfile.txt (Path preserved, extension appended)
• C:\version.1.0\myfile.bak + .txt -> C:\version.1.0\myfile.txt (Correctly replaced .bak with .txt)
• myfile.bak + .txt -> myfile.txt (Standard filename replaced)
• myfile + .txt -> myfile.txt (Appended without truncation)