unreachable-code

Flag statements that follow an unconditional return() or stop() in a block—once either runs, nothing after it in the same block can be reached, so the trailing code is dead. A direct-statement if/else that exits in both branches likewise leaves its tail unreachable (a control-flow-graph verdict).

The rule fires only when the terminator is a direct statement of the block (a lone return()/stop() guarded by an if leaves the tail reachable) and only when the callee resolves to base R; a local redefinition is left alone. return is additionally required to sit inside a function. The deletion fix is unsafe, and withheld when it would drop a comment.

This rule is enabled by default.

A statement after return() can never run:

f <- function() {
  return(1)
  2
}

warning: unreachable-code
 --> example.R:3:3
  |
3 |   2
  |   ^ code after `return()` can never be reached
  = help: Remove the unreachable code, or fix the control flow.

An if/else that exits in both branches leaves its tail dead:

f <- function() {
  if (x) return(1) else return(2)
  3
}

warning: unreachable-code
 --> example.R:3:3
  |
3 |   3
  |   ^ code after this `if` can never be reached (both branches exit)
  = help: Remove the unreachable code, or fix the control flow.