Add test, fix #15835

Author: TheElectronWill

tests/coverage/run/extend-case-class/test.check

@@ -0,0 +1,2 @@
+1
+6178

tests/coverage/run/extend-case-class/test.scala

@@ -0,0 +1,10 @@
+// see issue 15835
+import java.math.MathContext
+case class DecimalConf(mathContext: MathContext, scaleLimit: Int, digitsLimit: Int)
+object DecimalConf extends DecimalConf(MathContext.UNLIMITED, 6178, 308)
+
+@main
+def Test: Unit =
+  val c = DecimalConf(MathContext.DECIMAL32, 1, 0)
+  println(c.scaleLimit)
+  println(DecimalConf.scaleLimit)

tests/coverage/run/extend-case-class/test.scoverage.check

@@ -0,0 +1,71 @@
+# Coverage data, format version: 3.0
+# Statement data:
+# - id
+# - source path
+# - package name
+# - class name
+# - class type (Class, Object or Trait)
+# - full class name
+# - method name
+# - start offset
+# - end offset
+# - line number
+# - symbol name
+# - tree name
+# - is branch
+# - invocations count
+# - is ignored
+# - description (can be multi-line)
+# '' sign
+# ------------------------------------------
+0
+extend-case-class/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+282
+303
+8
+println
+Apply
+false
+0
+false
+println(c.scaleLimit)
+
+1
+extend-case-class/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+306
+337
+9
+println
+Apply
+false
+0
+false
+println(DecimalConf.scaleLimit)
+
+2
+extend-case-class/test.scala
+<empty>
+test$package$
+Object
+<empty>.test$package$
+Test
+206
+220
+6
+Test
+DefDef
+false
+0
+false
+@main\ndef Test
+