Intellisense not using IAR include paths (C++ MSP430)

[LukasP]

With the default configuration, intellisense can't find any includes outside of my project folders even though includePath in c_cpp_properties.json contains the compiler include directories:

"includePath": [
    "C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc\\dlib",
    "C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc",
    "C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc\\dlib\\c",
    "C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc\\dlib\\ecpp"
    // project specific dirs omitted
]

Intellisense helpfully offers: #include errors detected based on information provided by the configurationProvider setting. Squiggles are disabled for this translation unit

To Reproduce
1: install the extension
2: add IAR compiler path, workbench path and project file for MSP430 C++ project
3: include a header eg <cstdint>

Additional context
If I comment out "configurationProvider": "pluyckx.iar-vsc" in c_cpp_properties.json, intellisense does find headers in the IAR include paths, checked by Go to Definition of a header and looking at the file path.

[LukasP]

Looking at the C/C++ log diagnostics it seems the Translation Unit Configurations for each file do not have the IAR directories in the includes list, only the project specific directories.

I'd like to test if this is what causes the issue by adding the IAR paths to each file's generated include list but idk how to get the extension to run with modifications (never did anything with js/ts):

In includepath.ts:

    export function fromCompilerOutput(output: string): IncludePath[] {
        let includes: IncludePath[] = [];

        let regex = /\$\$INC_BEGIN\s\$\$FILEPATH\s\"([^"]*)/g;
        let result: RegExpExecArray | null = null;
        do {
            result = regex.exec(output);

            if (result !== null && (result.length === 2)) {
                let p = result[1].replace(/\\\\/g, "\\");

                try {
                    let stat = Fs.statSync(p);

                    if (stat.isDirectory()) {
                        includes.push(new StringIncludePath(p));
                    }
                } catch (e) {
                }
            }
        } while (result);

        includes.push(new StringIncludePath("C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc"));
        includes.push(new StringIncludePath("C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc\\dlib"));
        includes.push(new StringIncludePath("C:\\Program Files (x86)\\IAR Systems\\Embedded Workbench 8.5\\430\\inc\\dlib\\c"));

        return includes;
    }