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No 'comparing unrelated types' warning for functions #9675

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scabug opened this issue Feb 25, 2016 · 3 comments
Closed

No 'comparing unrelated types' warning for functions #9675

scabug opened this issue Feb 25, 2016 · 3 comments
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help wanted
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2.12.2

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@scabug
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scabug commented Feb 25, 2016

scalac 2.11.6 compiler gives useful warnings about unrelated types comparsion for expression, method, and functions.

scalac 2.11.7 doesn't give warning for functions.

case class A(x: String)

object App {

  // No warning with 2.11.7
  val func1 = (x: A) ⇒ { x != "x" }

  // No warning with 2.11.7
  val func2  = (x: A) ⇒ { x != "x" }: Boolean

  // No warning with 2.11.7
  val func3: Function1[A, Boolean] = (x) ⇒ { x != "x" }

  // Warning in method `apply` appeared
  val func4 = new Function1[A, Boolean] {
    def apply(x: A): Boolean = { x != "x" }
  }

  // Warning appeared
  def method(x: A): Boolean = { x != "x" }

  def main(args: Array[String]) {

    // Warning appeared
    A("x") != "x"

    // No warning with 2.11.7
    val func4: Function1[A, Boolean] = (x) ⇒ { x != "x" }

    // No warning with 2.11.7
    List(A("x")).foreach((item: A) ⇒ item != "x")
  }
}

Output of the scalac 2.11.7 and 2.12.0-M3 are the same:

[warn] C:\...\App.scala:18: comparing values of types abc.A and String using `!=' will always yield true
[warn]     def apply(x: A): Boolean = { x != "x" }
[warn]                                    ^
[warn] C:\...\App.scala:22: comparing values of types abc.A and String using `!=' will always yield true
[warn]   def method(x: A): Boolean = { x != "x" }
[warn]                                   ^
[warn] C:\...\App.scala:27: comparing values of types abc.A and String using `!=' will always yield true
[warn]     A("x") != "x"
[warn]            ^
[warn] three warnings found

Output of the scalac 2.11.6 (desired behaviour)

 C:\...\App.scala:8: comparing values of types abc.A and String using `!=' will always yield true
   val func1 = (x: A) ? { x != "x" }
                            ^
 C:\...\App.scala:11: comparing values of types abc.A and String using `!=' will always yield true
   val func2  = (x: A) ? { x != "x" }: Boolean
                             ^
 C:\...\App.scala:14: comparing values of types abc.A and String using `!=' will always yield true
   val func3: Function1[A, Boolean] = (x) ? { x != "x" }
                                                ^
 C:\...\App.scala:18: comparing values of types abc.A and String using `!=' will always yield true
     def apply(x: A): Boolean = { x != "x" }
                                    ^
 C:\Users\easy\sandbox\sbt-hide-warnings\src\main\scala\icm\App.scala:22: comparing values of types abc.A and String using `!=' will always yield true
   def method(x: A): Boolean = { x != "x" }
                                   ^
 C:\Users\easy\sandbox\sbt-hide-warnings\src\main\scala\icm\App.scala:27: comparing values of types abc.A and String using `!=' will always yield true
     A("x") != "x"
            ^
 C:\Users\easy\sandbox\sbt-hide-warnings\src\main\scala\icm\App.scala:30: comparing values of types abc.A and String using `!=' will always yield true
     val func4: Function1[A, Boolean] = (x) ? { x != "x" }
                                                  ^
 C:\..\App.scala:33: comparing values of types abc.A and String using `!=' will always yield true
     List(A("x")).foreach((item: A) ? item != "x")
                                           ^
 8 warnings found
@scabug
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scabug commented Feb 25, 2016

Imported From: https://issues.scala-lang.org/browse/SI-9675?orig=1
Reporter: andy legkiy (easy)
Affected Versions: 2.11.7, 2.11.8, 2.12.0-M3

@scabug
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scabug commented Feb 16, 2017

@adriaanm said:
scala/scala#5662

@scabug
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scabug commented Feb 16, 2017

@adriaanm said:
Fixed by @teldosas

@scabug scabug closed this as completed Feb 16, 2017
@scabug scabug added this to the 2.12.2 milestone Apr 7, 2017
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