Fix UnnecessaryLet false positive in inner lambdas

[xouabita]

When upgrading detekt to 1.7.1, I noticed some false positives for UnnecessaryLet.

For example:

fun callMe(callback: () -> Unit) {
    callback()
}
 
fun test(value: Int?) {
    value?.let { 
        callMe {
            println(it)
        }
     }
}

would be reported.

This PR should fix the issue

[codecov]

Codecov Report

Merging #3841 (b4cdcde) into main (a3df280) will decrease coverage by 0.00%.
The diff coverage is 70.00%.

@@             Coverage Diff              @@
##               main    #3841      +/-   ##
============================================
- Coverage     83.58%   83.57%   -0.01%     
  Complexity     3110     3110              
============================================
  Files           456      456              
  Lines          8931     8932       +1     
  Branches       1748     1747       -1     
============================================
  Hits           7465     7465              
  Misses          551      551              
- Partials        915      916       +1     

Impacted Files	Coverage Δ
...ab/arturbosch/detekt/rules/style/UnnecessaryLet.kt	80.00% <66.66%> (-2.36%)	⬇️
...tlab/arturbosch/detekt/rules/KtLambdaExpression.kt	66.66% <75.00%> (+9.52%)	⬆️

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[BraisGabin]

That doesn't seem as a false positive. It could be replaced with an if.

[xouabita]

@BraisGabin from the docs

a?.let { print(it) }

is compliant

[xouabita]

also,

fun callMe(callback: () -> Unit) {
    callback()
}
fun test(value: Int?) {
    value?.let { 
        callMe {
            it.plus(it)
        }
     }
}

would also be reported, which is a false positive

[BraisGabin]

You are right. For me that's an unnecessary usage but this rule, right now, should not flag it.

[xouabita]

Hi, thank you very much for reviewing this PR. Is there anything else I need to do before this PR can be merged ?

[BraisGabin]

I don't think so. Sorry for the late merge and thanks for the fix :)