False positive `KDOC_WITHOUT_RETURN_TAG` for functions returning `Unit` (implicit) or `Nothing` (explicit)

[0x6675636b796f75676974687562]

DiKTat should require no @return tags in KDoc comments for expression-body functions with an implicit Unit or an explicit Nothing return types. In the below cases, a KDoc without any @return tag is sufficient:

/**
 * This function does nothing.
 */
fun f1() = Unit

/**
 * This function does nothing.
 */
fun f2() = kotlin.Unit

/**
 * This function fails immediately.
 */
fun fail1(): Nothing = TODO()

/**
 * This function fails immediately.
 */
fun fail2(): kotlin.Nothing = TODO()

Environment information

• diktat version: 1.2.0
• build tool (maven/gradle): Maven
• how is diktat run (CLI, plugin, etc.): Maven plug-in
• kotlin version: 1.7.0
• operating system: Windows

[orchestr7]

Zero priority, not critical at all (keeping in mind the number of issues we have).

[petertrr]

I think we decided to check only explicit Unit because without type resolution it is too complex to check actual return type. Explicit Nothing, OTOH, can be easily added along with explicit Unit