Type: LanguageService

Describe the bug

• OS and Version: macOS 10.15.1 (Catalina)
• VS Code Version: 1.40.2
• C/C++ Extension Version: 0.26.2
• Other extensions you installed (and if the issue persists after disabling them): Python, Rust (rls) (both disabled without any change)
• A clear and concise description of what the bug is:

If the project path contains an umlaut like ü, no red squiggles are shown in the editor, even if problems are detected and shown in the Problems tab.

To Reproduce

1. Create a project directory with a name that contains an umlaut (e.g., ~/tüst)
2. Open in vscode and create an erronous C file, e.g.:

int main() {
  @;
}

3. Wait until the problem is detected and listed in the Problems tab
4. Observe: No squiggly line below the @
5. Close vscode and rename project directory, e.g. from tüst to test
6. Open file in vscode again and wait until problem is detected and listed in the Problems tab
7. Observe: Squiggly line below the @

One additional thing:
If you click on the error listed in the Problems tab, the file is opened using an abolute path. In this new file tab, the squiggles are shown as expected, even if the path contains an umlaut.

Expected behavior

The squiggles should work regardless of the file location.

Screenshots

With umlaut, no squiggles:

With umlaut, opened with aboslut path, squiggles working:

No umlaut, squiggles working:

Additional context

I tried to reproduce the problem with the Python extension but could not, so I assume it is an issue specific to vscode-cpptools.