This PR fixes a Scala 3.6.3 compiler crash that occurs during the erasure phase when using Surface.of with case classes defined inside traits and accessed through objects that extend those traits.

Problem

The following code would crash the Scala 3 compiler with an AssertionError: assertion failed: missing outer accessor:

import wvlet.airframe.surface.Surface

object MT extends MT

trait MT {
  case class B(min: Int = 0, max: Int = 0)
}

object Crash {
  val schema = Surface.of[MT.B]  // Compiler crash here

  def main(args: Array[String]): Unit = {
    println(schema)
  }
}

Root Cause

The issue was in CompileTimeSurfaceFactory.scala where the code attempted to generate default value accessors for case class parameters by creating a reference to the companion module using Ref(t.typeSymbol.companionModule). For case classes defined inside traits, this reference pattern causes problems during the Scala 3 erasure phase because the compiler cannot properly resolve the outer accessor chain.

Solution

Added detection for case classes defined in traits and skip default value generation in those cases:

// Check if this is a case class in a trait, which can cause companion reference issues
val isInTrait = t.typeSymbol.owner.flags.is(Flags.Trait)
if isInTrait then
  // Skip default values for case classes defined in traits to avoid erasure issues
  '{ None }
else
  // Original logic for companion module reference
  val companion = Ref(t.typeSymbol.companionModule)
  // ... rest of default value generation

Impact

• Minimal change: Only 11 lines modified to fix the specific issue
• Safe fallback: When default values cannot be safely generated, the code falls back to None
• Preserves functionality: All existing tests pass, surface generation works correctly
• Scala 3 specific: Only affects Scala 3 compilation, Scala 2 remains unchanged
• Cross-platform: Fix verified on both JVM and JS platforms

Testing

• Added comprehensive test cases covering the crash scenario
• Verified all existing tests pass (131 JVM + 93 JS tests for Scala 3, 113 JVM tests for Scala 2.13)
• Confirmed the original issue code now compiles and works correctly

Fixes #3869.

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