Defining any method named conforms breaks Scala collections

[scabug]

This is a fun one:

scala> class C {
     |   def conforms(x: Int, y: Int) = x < y
     |   val xs = List((1, 2), (3, 4))
     |   println(xs.unzip)
     | }
<console>:11: error: No implicit view available from (Int, Int) => (A1, A2).
         println(xs.unzip)              ^

The problem is that Predef.conforms is shadowed by the local conforms. It took me a while to figure out what happened.

IMO this is a trap waiting to happen for everyone. We should avoid it by finding a less conspicuous name for the conversion. Ideally with a dollar in it.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-7788?orig=1
Reporter: @odersky
Affected Versions: 2.10.3

[scabug]

@retronym said:
Special treatment of this method name is hard-coded in the IntelliJ presentation compiler's implicit search; we'll have to notify them if/when we change.

[scabug]

@retronym said:
I'm thinking that I might add a(nother) special case for conforms to disable shadowing checks.

In doing so, I found some problems with the roundabout way that implicit search detects and reports shadowing, so I'll fix that too.

WIP: https://github.com/retronym/scala/compare/topic;7788?expand=1

[scabug]

@retronym said:
scala/scala#3217

[scabug]

@adriaanm said:
how about deprecating Predef.conforms, removing its implicit status, and adding a implicit def __$MAGIC$__conforms to Predef?

[scabug]

@adriaanm said:
scala/scala#3555