Some files won't edit because url is a directory or it doesn't follow any of your class kinds, to fix this in P4XcodeHelper.m I added this the currentSourceCodeDocument when all of the known ones fail.

if ([currentEditor respondsToSelector:@selector(document)]) {
    IDESourceCodeDocument *document = (IDESourceCodeDocument *)[currentEditor document];

    return document;
}

Also in method currentSourceCodeDocumentURL added this.

    if ([[NSFileManager defaultManager] fileExistsAtPath:[docURL path] isDirectory:&isDirectory]) {
        if (isDirectory) {
            NSString *path = [docURL path];
            path = [path stringByAppendingPathComponent:@"project.pbxproj"];
            if ([[NSFileManager defaultManager] fileExistsAtPath:[docURL path]]) {
                docURL = [NSURL fileURLWithPath:path];
            }
        }
    }

This will allow the project file .xcodeproj to check out the project file because the project file is a package.

This doesn't seem to be an open source project would have made the changes myself if it was.