Wrong staging level is inferred when a variable is used in a HOAS pattern over splice/quote redex

[zeptometer]

Compiler version

3.3.0

Minimized code

import scala.quoted.*

def testExprImpl(body: Expr[Any])(using Quotes): Expr[String] =
  body match
    case '{ (a:Int) => (${'{1 + ($b(a) : Int)}} : Int) } =>
      '{ $b(1).toString }
    case _ => Expr("not matched"
)

Output

-- Warning: Macro.scala:6:24 ---------------------------------------------------
6 |    case '{ (a:Int) => (${'{1 + ($b(a) : Int)}} : Int) } =>
  |                        ^^^^^^^^^^^^^^^^^^^^^^^
  |Canceled quote directly inside a splice. ${ '{ XYZ } } is equivalent to XYZ.
-- Error: Macro.scala:6:36 -----------------------------------------------------
6 |    case '{ (a:Int) => (${'{1 + ($b(a) : Int)}} : Int) } =>
  |                                    ^
  |                           access to parameter a from wrong staging level:
  |                            - the definition is at level 0,
  |                            - but the access is at level 1.
1 warning found
1 error found

Expectation

• If the working message is correct, it should compile as well as case '{ (a:Int) => 1 + ($b(a) : Int) } =>.
• or, considering the behavior of (hoas) splice pattern, it is also reasonable to to conclude that $'{...} is not equivalent to ... as a pattern. In this case, we want to change the warning message.
  • The current error message informal about staging level, which seems not right. Instead, it should show an error message like "a is undefined in this scope".

[nicolasstucki]

This should be disallowed. The nested pattern cannot user outer variables in its hoas captures. We need give a better error message.