Why are mutants generated that will be filtered out by the mutate filter anyways?

[causa-prima]

I want to check my tests for a new file I created and don't want to waste time. Thus, I put the file I want to mutate to as the only entry to the mutate parameter. Still, mutants for other files seem to be created, as the output states that 19940 mutants got status Ignored. Reason: Removed by mutate filter. I do not understand why these mutants got generated in the first place, when they will be filtered out anyway. I would expect that when generating the mutants for a file, it is first checked whether the file would be filtered out by the mutate parameter. In my case, this would probably save a lot of time.

Am I missing something and this won't work, or should I create a feature request?

Note: I understand that filtering out mutants before creating them would be hard(er) for the test-case-filter parameter, but for the mutate filter I would expect it to be relatively easy, so I don't understand why this filter is applied only after the mutants have already been created.

[dupdob]

Currently all possible mutations are generated, disregarding their potential filtered state. There are several reasons:

1. the filter step happens after mutation generation
2. mutation generation is actually quite fast
3. generating all mutations ensure overall numbers remain somewhat consistent across runs

you can open an issue for this, but I suggest you provide the timing you experience (use -L to get log filed)