Strange compiler bug caused by some sort of misidentified name conflict

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object ConfigExampleApp extends App {
  case class Config(name: String = null)
  val parser = new scopt.immutable.OptionParser[Config]("a", "b") {
    def options = Seq(
      arg("name", "the name of something") {
        (value, conf) => conf.copy(name = value)
      }
    )
  }
  val config = parser.parse(args, new Config).get
  val name = config.name
}

you will need a jar of https://github.com/jstrachan/scopt to resolve that dependency.

In this case, i get an error "no value value" on the (name = value) section in the middle. It turns out to be caused by the overlap of the name of "val name" and "Config.name". If I rename either of those, the code compiles.

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Imported From: https://issues.scala-lang.org/browse/SI-7381?orig=1
Reporter: Mike Schrag (mschrag)
Affected Versions: 2.10.0
Duplicates #5044
Attachments:

• scopt_2.10-2.1.0.jar (created on Apr 17, 2013 6:34:47 PM UTC, 124199 bytes)

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Mike Schrag (mschrag) said:
whoops, that should be https://github.com/scopt/scopt . i sent the older link inadvertently.

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Mike Schrag (mschrag) said:
adding the same jar I'm using

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@paulp said:
Have you tried and failed to reproduce this without the dependency? It seems unlikely this is specific to scopt.

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Mike Schrag (mschrag) said:
It's almost certainly not scoot-specific, but isolating it was becoming tricky. The error is inside of the inner function, but it's caused by the naming outside the function. If I completely remove the entire middle scopt section, it works. I tried a slightly larger example and it worked as well, so I figured I'd go ahead and just file it with the dependency. I figured you guys might be able to more quickly see the problem outright compared to me trying to narrow the test case further.

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@paulp said:
Duplicate of #5044.

If you compile with 2.10.1 instead of 2.10.0, you will get a better error message.

./7381.scala:9: error: not found: value value
        (value, conf) => conf.copy(name = value)
                                          ^
./7381.scala:9: warning: type-checking the invocation of method copy checks if the named argument expression 'name = ...' is a valid assignment
in the current scope. The resulting type inference error (see above) can be fixed by providing an explicit type in the local definition for name.
        (value, conf) => conf.copy(name = value)
                                        ^
one warning found
one error found

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@paulp said:
And indeed if I do as it suggests, "val name: String = config.name", it compiles.

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Mike Schrag (mschrag) said:
Sadly, I just finished a more narrow test case of it, too. Thanks, Paul.