Error about Contextual function's parameter refer to its synthetic name without explantation

[Sporarum]

Compiler version

3.3.1-RC1

Minimized code

class A1[T](action: A1[T] ?=> String = "")

Output

-- [E081] Type Error: ----------------------------------------------------------
1 |class A1[T](action: A1[T] ?=> String = "")
  |                                       ^
  |                   Missing parameter type
  |
  |                   I could not infer the type of the parameter evidence$1.
  |                   What I could infer was: A1[<?>]
1 error found

Expectation

The error mentions evidence$1 which is not defined anywhere
(neither in user-facing code, nor in the error message)

This example was taken from tests/neg/i11350.scala in the compiler, but affects any AnonymousFunctionMissingParamType on contextual functions, and potentially other errors

[Sporarum]

It should be relatively straightforward to fix at least for AnonymousFunctionMissingParamType

[Sporarum]

@smarter also talked about adding this behavior to the interpolator directly, which would be more challenging, but can still be interesting for spree pros

[bishabosha]

as well as having a confusing error message, this seems to be a bug in inference because the following (obvious desugaring) type-checks without error:

class A1[T](action: A1[T] ?=> String = (a1: A1[T]) ?=> "")

[bishabosha]

perhaps we should make a separate issue about the infamous "I could not infer the type of the parameter foo$1" when using placeholder parameters