Dynamic doesn't compile with Typeclass

[sequencer]

Compiler version

3.5.2

Minimized code

import scala.language.dynamics

trait DynamicHello[E] extends Dynamic:
  extension (ref: E)
    def selectDynamic(
      field: String
    ): Any

given DynamicHello[String] with
  extension (ref: String)
    override def selectDynamic(field: String) = s"Hello $field"

// Doesn't compile with error:
// value hello is not a member of String [15:6]
def badHello(str: String) =
  str.hello

// compile, and prove `DynamicHello[String]` does give to `String`
def goodHello(str: String) =
  str.selectDynamic("hello")

Output

[info] compiling 1 Scala source to xxx ...
[error] -- [E008] Not Found Error: Example.scala:15:6
[error] 18 |  str.hello
[error]    |  ^^^^^^^^^
[error]    |  value hello is not a member of String
[error] one error found

May relate to #17106

[sjrd]

As designed. The spec specifically forbids the Dynamic treatment after an implicit conversion, which also covers extension methods.

[sequencer]

Hi, @sjrd can you point out the source of spec here? I think this issue is similar with #17106

[sjrd]

https://www.scala-lang.org/files/archive/spec/3.4/06-expressions.html#dynamic-member-selection

Notice

assuming e's type conforms to scala.Dynamic

For it to conform to scala.Dynamic, it must be a true subtype. It cannot become a scala.Dynamic after an implicit conversion.