S011 finally_close

Off by default. Fixable with --fix.

$ scruff check --select finally_close --fix

# or, alternatively
$ scruff check --select S011 --fix

--select runs this rule, and only it, without changing the configuration. To keep it on, add it to extend-select under [lint].

Description

Flags a try without catch whose finally only closes a resource, as in try { ... } finally a.close(). It points at try.

Why is this bad?

scala.util.Using's resource function can express this.

Fix

--fix rewrites val a = ... and the try right after it to Using.resource(...): a =>, with braces outside Scala 3, and imports scala.util.Using.

Example

Given this A.scala, in the scala3 dialect:

package example

import java.io.FileInputStream

object A:
  def f1: Int =
    val a = new FileInputStream("a")
    try
      val b = a.read()
      val c = a.read()
      b + c
    finally a.close()

scruff check --select finally_close --fix rewrites it to:

package example

import java.io.FileInputStream
import scala.util.Using

object A:
  def f1: Int =
    Using.resource(new FileInputStream("a")): a =>
      val b = a.read()
      val c = a.read()
      b + c

and prints Found 1 problem (1 fixed, 0 remaining)., exiting with 0.