Add rule [RedundantSuspend] to detect redundant suspend modifiers

[tobiasschuerg]

There is already an inspection inside Intellij:

This inspection reports a suspend modifier as redundant if no other suspend functions are called inside.

Expected Behavior of the rule

Detects usages of suspend modifiers that are useless because the function is not suspendable.

suspend fun hello() {
  retrun "hello"
}

Context

• https://kotlinlang.org/docs/reference/coroutines/basics.html#coroutine-basics
• https://stackoverflow.com/a/54560740/570168

[schalkms]

Good idea! Thanks for submitting this nice idea. 😊
Do you have some resources to help us out here? @tobiasschuerg
Any help is highly appreciated.

[schalkms]

This rule should also go into the concurrenty ruleset. Please see my comment in #2155

[xouabita]

For reference:

• https://github.com/JetBrains/kotlin/blob/master/idea/src/org/jetbrains/kotlin/idea/inspections/RedundantSuspendModifierInspection.kt
• https://github.com/JetBrains/kotlin/blob/354f8f0bf16844936fd8a6c9cffcf27ec322bc7d/idea/src/org/jetbrains/kotlin/idea/highlighter/KotlinSuspendCallLineMarkerProvider.kt#L86