Fix UseDataClass to accept classes that implement interfaces

[zsmoore]

Addresses issue #2904

Root cause is that our doesNotExtendAnything() considers interfaces.

There is not a very easy way to fix this, the fix I have done to detect interfaces is

• Look at the UserType
• Go to the containing KT File
• Find the declaration with the referenced name
• See if that declaration is a KTClass and an interface

From what I searched PSI does not give us many tools to get class from superTypeEntry

[codecov]

Codecov Report

Merging #2905 into master will decrease coverage by 0.02%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master    #2905      +/-   ##
============================================
- Coverage     80.18%   80.15%   -0.03%     
- Complexity     2426     2429       +3     
============================================
  Files           421      421              
  Lines          7378     7384       +6     
  Branches       1350     1354       +4     
============================================
+ Hits           5916     5919       +3     
- Misses          762      764       +2     
- Partials        700      701       +1     

Impacted Files	Coverage Δ	Complexity Δ
...turbosch/detekt/rules/KtClassOrObjectExtensions.kt	40.00% <33.33%> (-26.67%)	0.00 <0.00> (ø)
...tlab/arturbosch/detekt/rules/style/UseDataClass.kt	76.36% <100.00%> (+1.81%)	38.00 <0.00> (+2.00)
...lab/arturbosch/detekt/core/FileProcessorLocator.kt	69.23% <0.00%> (-10.77%)	5.00% <0.00%> (ø%)
...ab/arturbosch/detekt/cli/DetektProgressListener.kt	83.33% <0.00%> (+3.33%)	4.00% <0.00%> (+1.00%)

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[cortinico]

Looks good to me. I've left a minor comment on the tests. If you could add a couple more it would be better 👍

[cortinico]

Can I ask you to please write two other tests:

interface SimpleInterface {
    val i: Int
}

data class DataClass(override val i: Int): SimpleInterface

This should not report anything as you're correctly already using a data class.
And this other test:

interface SimpleInterface {
    val i: Int
}

open class BaseClass(open val j: Int)

class DataClass(override val i: Int, override val j: Int): SimpleInterface, BaseClass(j)

This should also report nothing as you're extending from another class (and an interface).

[zsmoore]

Added additional tests and looks like they pass. Great test suggestions thanks!

[zsmoore]

Also as a note added myself to the readme for this one +
#2258
#2262
#2263