Adds a ForbiddenSingleExpressionSyntax rule

[marschwar]

closes #1675

While trying to find a reference for the rule documentation, I realized that there does not seem to be agreement about this in the community. I guess this will never become a rule that is turned on be default.

While I personally like the rule, I am wondering if detekt should even be so opinionated about things that are not part of the official coding conventions or guidelines.

And then I may have formatting issues (again). Opening any other rule class causes the ktlint plugin to report an error such as Unexpected indentation (20) (should be 12) (indent). Any help will be greatly appreciated.

[codecov]

Codecov Report

Merging #3550 (f3d4f2e) into master (bdceacb) will increase coverage by 0.00%.
The diff coverage is 82.60%.

@@            Coverage Diff            @@
##             master    #3550   +/-   ##
=========================================
  Coverage     77.53%   77.54%           
- Complexity     2829     2839   +10     
=========================================
  Files           464      465    +1     
  Lines          8769     8790   +21     
  Branches       1713     1719    +6     
=========================================
+ Hits           6799     6816   +17     
  Misses         1046     1046           
- Partials        924      928    +4     

Impacted Files	Coverage Δ	Complexity Δ
...osch/detekt/rules/exceptions/SwallowedException.kt	77.35% <ø> (ø)	19.00 <0.00> (ø)
...t/rules/style/ForbiddenSingleExpressionFunction.kt	80.00% <80.00%> (ø)	10.00 <10.00> (?)
...n/io/github/detekt/report/sarif/RuleDescriptors.kt	20.00% <100.00%> (ø)	0.00 <0.00> (ø)
...rturbosch/detekt/rules/style/StyleGuideProvider.kt	100.00% <100.00%> (ø)	3.00 <0.00> (ø)

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[BraisGabin]

While I personally like the rule, I am wondering if detekt should even be so opinionated about things that are not part of the official coding conventions or guidelines.

We talked about this a lot of times in different issues. We need a controversial ruleset. But I also like this rule a lot. And I know other devs that don't like the overuse of this feature either.

And then I may have formatting issues (again). Opening any other rule class causes the ktlint plugin to report an error such as Unexpected indentation (20) (should be 12) (indent). Any help will be greatly appreciated.

We can open a new issue about this topix. I think that we should enable ktlint in this project. I have the same issue autoformatting some rules that it changes far too much lines.

[schalkms]

This suppression shouldn't be necessary, since the guard clause having a return statement are excluded.

[schalkms]

We need a controversial ruleset.

I suggested this in a few PRs as well. +1 from my side.

[marschwar]

How about I at least add a @controversial to the kdoc?

[BraisGabin]

Great idea!!! Yes! We can add the rules in any ruleset but we can mark them as controversial! I think that we can make a new issue to implement this idea and merge this directly. The annotation is a better solution and it is not a breaking change so we can even mark old rules. Win-win!

[marschwar]

I think this is obsolete as there is already a ImplicitUnitReturnType rule that checks the exact same case.