New Check: AvoidFinalConditionInversion

[romani]

We need a check that could catch "not" operator - "!" (an exclamation mark) that is used as final operation, but it is possible without changing a meaning of condition change its parts to make condition more readable.

Bad code examples:
isDifferent(): return ! (a == b); ==should be==> return a != b;
isLower(): boolean c = !(a > b); ==should be==> boolean c = a <= b;
isLowerLimits(): if (! ((a>=8) && (b>=5)) ) ==should be==> if ((a<8) || (b<5))

Big example (not sure we could catch such cases):

return !(timeLoadMlls < maxMasterSymbolLoadStampMills 
          && fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART) 
          || timeLoadMlls < maxOtherLoadStampMills 
          && !fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART));

==should be==>

return (timeLoadMlls >= maxMasterSymbolLoadStampMills 
           || !fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART) 
           && timeLoadMlls >= maxOtherLoadStampMills 
           || fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART));

[romani]

that Check might be similar to https://github.com/sevntu-checkstyle/sevntu.checkstyle/blob/master/sevntu-checks/src/main/java/com/github/sevntu/checkstyle/checks/coding/ConfusingConditionCheck.java

[alexkravin]

It would be a good idea to insert "how to avoid" advice into violation message, but sure it's impossible to cover all cases, so Check has to put violation like (Condition inversion could be avoided.)

[alexkravin]

That should be done in: return, loops and if conditions, right?

[romani]

Message should be simple, do not propose solution.

Yes, loops, if , returns should be checked.

Beware that check might find some very debatable cases, please run it on big projects and try to make sure that code would become better after required changes (some additional options might be required)

[alexkravin]

discussion thread: https://groups.google.com/forum/#!topic/sevntu-checkstyle/KlQhTDDlhZA

[romani]

implemented by Alexey.

[rdiachenko]

if (! ((a>=8) && (b>=5)) ) ==should be==> if ((a<8) && (b<5))

---

return !(timeLoadMlls < maxMasterSymbolLoadStampMills
&& fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART)
|| timeLoadMlls < maxOtherLoadStampMills
&& !fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART));
==should be==>
return (timeLoadMlls >= maxMasterSymbolLoadStampMills
&& fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART)
|| timeLoadMlls >= maxOtherLoadStampMills
&& !fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART));

According to De Morgan's lows the resulted expressions should be as follows:

if (! ((a>=8) && (b>=5)) ) ==should be==> if ((a<8) || (b<5))

and

return !(timeLoadMlls < maxMasterSymbolLoadStampMills 
&& fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART) 
|| timeLoadMlls < maxOtherLoadStampMills 
&& !fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART));

==should be==>

return (timeLoadMlls >= maxMasterSymbolLoadStampMills 
|| !fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART) 
&& timeLoadMlls >= maxOtherLoadStampMills 
|| fileName.toLowerCase().contains(MASTER_SYMBOL_NAME_PART));

[romani]

description was updated.