It's easy to test the feature_set problem also by adding an invalid setting to launch.json, like this:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Listen for XDebug",
            "type": "php",
            "request": "launch",
            "port": 9000,
            "xdebugSettings": {
                "invalid": true
            },
            "log": false
        },
        {
            "name": "Launch currently open script",
            "type": "php",
            "request": "launch",
            "program": "${file}",
            "cwd": "${fileDirname}",
            "port": 9000
        }
    ]
}

make sure that invalid settings don't prevent init from completing

Unsure about this path. Why do you think is it okay to continue if the features failed? Why shouldn't we error the request (which should result in a toast vs just a log message)?

Codecov Report

Merging #243 into master will decrease coverage by 0.25%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #243      +/-   ##
==========================================
- Coverage    69.6%   69.35%   -0.26%     
==========================================
  Files           5        5              
  Lines         987      992       +5     
  Branches      160      161       +1     
==========================================
+ Hits          687      688       +1     
- Misses        300      304       +4

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Since the settings are normally not critical for the debugger to work, I thought logging it in debug console would be better than aborting the whole process. I was also thinking that there might be other situations where setting an otherwise valid feature is not allowed for some reason beyond my knowledge, so it might be safer, but if you believe that raising a toast and erroring the request is better, I'd be fine with that too.

@felixfbecker I think this is the best I can do. The latest commit fixes startup problems e.g. when there's already a debugger running in another window and aborts the debugger if applying xdebugSettings fails. I couldn't find a way to display a nicer toast, though.

@felixfbecker Any chance of getting this merged?