extension with using clauses with defaults and with a method with default argument fails at call site

[sjbiaga]

Compiler version

3.8.0-RC4

Minimized example

This may be a long shot, but... I have a rudimentary key-value language, where values may be keys in turn. Putting it shortly, the possible type-methods (named like boolean or int) are extension methods with receiver a String. The extension syntax employs using clauses with defaults.

For each extension method, another method is defined outside extensions with a default receiver. A "variable" is a pair (String, String).

For simplicity, the key is stored in a default: Option[String] variable.

implicit def ?[S, T](fun: S => T): S ?=> T = { it ?=> fun(it) }

case class RuntimeException2(`var`: (String, String), cause: Throwable) extends RuntimeException("" + `var` + cause.getMessage)

var default: Option[String] = Some("test")
var value: String = "0"

extension (self: String)
          (using err: String => ((String, String)) ?=> Throwable = { msg => `var` ?=> RuntimeException(msg + `var`) })
          (using key: () => String = () => default.get)
          (using `var`: (() => String) ?=> (String, String) = { key ?=> key() -> self })

  def boolean: Boolean =
    try
      self.toLowerCase.toBoolean
    catch _ => throw err("a boolean")

  def int(`type`: String = "an integer"): Int =
    try
      self.toInt
    catch _ => throw err(`type`)

  def pos: Int = int("a positive integer").abs

def boolean: Boolean = value.boolean
def int(`type`: String = "an integer"): Int = value.int(`type`) // the error is caused by this line
def pos: Int = value.pos(using { msg => RuntimeException2(_, cause = RuntimeException(msg)) })

The three using clauses in the extension work like this: given a (default) key (of type () => String), I can make a given (String, String) pair (the `var` third parameter), and then return a RuntimeException via the first err parameter.

Output Error/Warning message

-- [E081] Type Error: ----------------------------------------------------------
6 |          (using err: String => ((String, String)) ?=> Throwable = { msg => `var` ?=> RuntimeException(msg + `var`) })
  |                                                                     ^^^
  |                           Missing parameter type
  |
  |                           I could not infer the type of the parameter msg
-- [E081] Type Error: ----------------------------------------------------------
6 |          (using err: String => ((String, String)) ?=> Throwable = { msg => `var` ?=> RuntimeException(msg + `var`) })
  |                                                                            ^^^^^
  |                           Missing parameter type
  |
  |                           I could not infer the type of the parameter var
-- [E081] Type Error: ----------------------------------------------------------
8 |          (using `var`: (() => String) ?=> (String, String) = { key ?=> key() -> self })
  |                                                                ^^^
  |                           Missing parameter type
  |
  |                           I could not infer the type of the parameter key
-- [E008] Not Found Error: -----------------------------------------------------
19 |def int(`type`: String = "an integer"): Int = value.int(`type`)
   |                                              ^^^^^^^^^
   |value int is not a member of String.
   |An extension method was tried, but could not be fully constructed:
   |
   |    {
   |      val self$2: String = value
   |      val err$2:
   |        
   |          <error Missing parameter type
   |    
   |    I could not infer the type of the parameter msg>
   |           => (
   |          <error Missing parameter type
   |    
   |    I could not infer the type of the parameter var>
   |          ) ?=> <error unspecified error>
   |       = this.int$default$2(self$2)
   |      val key$2: () => String = this.int$default$3(self$2)(err$2)
   |      int(self$2)(using err$2)(using key$2)(using (using contextual$3: () => String)
   |         =>
   |        this.int$default$4(self$2)(err$2)(key$2).apply(/* missing */summon[<notype>]
   |          )
   |      )
   |    }
   |
   |    failed with:
   |
   |        No given instance of type <error Missing parameter type
   |        
   |        I could not infer the type of the parameter key> was found for parameter of (<error Missing parameter type
   |        
   |        I could not infer the type of the parameter key>
   |          ) ?=> <error unspecified error>
-- Error: ----------------------------------------------------------------------
19 |def int(`type`: String = "an integer"): Int = value.int(`type`)
   |    ^
   |    two or more overloaded variants of method int have default arguments
there was 1 feature warning; re-run with -feature for details
1 warning found
5 errors found