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Incorrect warning when using an overloaded 'eq' method #6328

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scabug opened this issue Sep 6, 2012 · 3 comments
Closed

Incorrect warning when using an overloaded 'eq' method #6328

scabug opened this issue Sep 6, 2012 · 3 comments
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@scabug
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scabug commented Sep 6, 2012

The following test case produces a warning, but I do not believe it should:

scala> object Foo { def eq(x:Int) = x }
defined module Foo

scala> Foo.eq(1)
<console>:9: warning: comparing values of types object Foo and Int using `eq' will always yield false
              Foo.eq(1)
                    ^
res0: Int = 1
@scabug
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scabug commented Sep 6, 2012

Imported From: https://issues.scala-lang.org/browse/SI-6328?orig=1
Reporter: Jared Luxenberg (jluxenberg)
Duplicates #6091

@scabug
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scabug commented Sep 6, 2012

Jared Luxenberg (jluxenberg) said:
The bug appears to be in RefChecks.scala:

...
    def checkSensible(pos: Position, fn: Tree, args: List[Tree]) = fn match {
      case Select(qual, name @ (nme.EQ | nme.NE | nme.eq | nme.ne)) if args.length == 1 =>
        def isReferenceOp = name == nme.eq || name == nme.ne

...

        // Whether def equals(other: Any) is overridden                                                                                                                                                                                     
        def isUsingDefaultEquals      = {
          val m = receiver.info.member(nme.equals_)
          (m == Object_equals) || (m == Any_equals)
        }
        // Whether this == or != is one of those defined in Any/AnyRef or an overload from elsewhere.                                                                                                                                       
        def isUsingDefaultScalaOp = {
          val s = fn.symbol
          (s == Object_==) || (s == Object_!=) || (s == Any_==) || (s == Any_!=)
        }
        // Whether the operands+operator represent a warnable combo (assuming anyrefs)                                                                                                                                                      
        def isWarnable           = isReferenceOp || (isUsingDefaultEquals && isUsingDefaultScalaOp)

note that isReferenceOp is "true" whenever the method name is "eq" or "ne". This code does not take into account whether the method has been overloaded. A check similar to the one used by "isUsingDefaultEquals" and "isUsingDefaultScalaOp" should be included for "eq" and "ne".

@scabug
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scabug commented Sep 7, 2012

@retronym said:
More or less a duplicate of #6091.

Dealing with name, rather than symbols, is perilous when creating or pattern matching against trees.

@scabug scabug closed this as completed Sep 7, 2012
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