Fix non-exhaustive warnings in the EveryReadIsExpression and GoReads

Move `createSubstreamBuffered` from `EveryReadIsExpression` to `CommonReads`
to make it available for `GoReads`

I'm not sure that Borrowed types is possible there but types allow them.
As a side effect, remove dead code

shared/src/main/scala/io/kaitai/struct/languages/components/CommonReads.scala

@@ -1,7 +1,7 @@
 package io.kaitai.struct.languages.components
 
 import io.kaitai.struct.datatype._
-import io.kaitai.struct.datatype.DataType.{SwitchType, UserTypeFromBytes, BytesType}
+import io.kaitai.struct.datatype.DataType.{ArrayTypeInStream, SwitchType, UserTypeFromBytes, BytesType}
 import io.kaitai.struct.exprlang.Ast
 import io.kaitai.struct.format._
 
@@ -116,4 +116,38 @@ trait CommonReads extends LanguageCompiler {
     */
   def attrValidateAll(attr: AttrLikeSpec) =
     attr.valid.foreach(valid => attrValidate(attr.id, attr, valid))
+
+  /**
+    * Creates a substream by reading bytes that will comprise the stream first into a buffer in
+    * memory, and then wrapping that buffer as a new stream.
+    * @param id identifier of a member that this stream is for
+    * @param byteType underlying bytes type
+    * @param io parent stream to derive substream from
+    * @param rep repeat specification for underlying bytes type
+    * @param defEndian default endianness specification
+    * @return string reference to a freshly created substream
+    */
+  def createSubstreamBuffered(
+    id: Identifier,
+    byteType: BytesType,
+    io: String,
+    rep: RepeatSpec,
+    defEndian: Option[FixedEndian]
+  ): String = {
+    val rawId = RawIdentifier(id)
+
+    attrParse2(rawId, byteType, io, rep, true, defEndian)
+
+    val extraType = rep match {
+      case NoRepeat => byteType
+      case _ => ArrayTypeInStream(byteType)
+    }
+
+    this match {
+      case thisStore: AllocateAndStoreIO =>
+        thisStore.allocateIO(rawId, rep)
+      case thisLocal: AllocateIOLocalVar =>
+        thisLocal.allocateIO(rawId, rep)
+    }
+  }
 }

shared/src/main/scala/io/kaitai/struct/languages/components/EveryReadIsExpression.scala

@@ -104,7 +104,10 @@ trait EveryReadIsExpression
       case knownSizeType: UserTypeFromBytes =>
         // we have a fixed buffer, thus we shall create separate IO for it
         createSubstream(id, knownSizeType.bytes, io, rep, defEndian)
-      case _: UserTypeInstream =>
+      case knownSizeType: CalcUserTypeFromBytes =>
+        // we have a fixed buffer, thus we shall create separate IO for it
+        createSubstream(id, knownSizeType.bytes, io, rep, defEndian)
+      case _: UserTypeInstream | _: CalcUserType =>
         // no fixed buffer, just use regular IO
         io
     }
@@ -176,33 +179,6 @@ trait EveryReadIsExpression
       None
     )
 
-  /**
-    * Creates a substream by reading bytes that will comprise the stream first into a buffer in
-    * memory, and then wrapping that buffer as a new stream.
-    * @param id identifier of a member that this stream is for
-    * @param byteType underlying bytes type
-    * @param io parent stream to derive substream from
-    * @param rep repeat specification for underlying bytes type
-    * @param defEndian default endianness specification
-    * @return string reference to a freshly created substream
-    */
-  def createSubstreamBuffered(id: Identifier, byteType: BytesType, io: String, rep: RepeatSpec, defEndian: Option[FixedEndian]): String = {
-    val rawId = RawIdentifier(id)
-
-    attrParse2(rawId, byteType, io, rep, true, defEndian)
-
-    val extraType = rep match {
-      case NoRepeat => byteType
-      case _ => ArrayTypeInStream(byteType)
-    }
-
-    this match {
-      case thisStore: AllocateAndStoreIO =>
-        thisStore.allocateIO(rawId, rep)
-      case thisLocal: AllocateIOLocalVar =>
-        thisLocal.allocateIO(rawId, rep)
-    }
-  }
 
   def attrSwitchTypeParse(
     id: Identifier,

shared/src/main/scala/io/kaitai/struct/languages/components/GoReads.scala

@@ -112,24 +112,10 @@ trait GoReads extends CommonReads with ObjectOrientedLanguage with GoSwitchOps {
   def attrUserTypeParse(id: Identifier, dataType: UserType, io: String, rep: RepeatSpec, defEndian: Option[FixedEndian]): Unit = {
     val newIO = dataType match {
       case knownSizeType: UserTypeFromBytes =>
-        // we have a fixed buffer, thus we shall create separate IO for it
-        val rawId = RawIdentifier(id)
-        val byteType = knownSizeType.bytes
-
-        attrParse2(rawId, byteType, io, rep, true, defEndian)
-
-        val extraType = rep match {
-          case NoRepeat => byteType
-          case _ => ArrayTypeInStream(byteType)
-        }
-
-        this match {
-          case thisStore: AllocateAndStoreIO =>
-            thisStore.allocateIO(rawId, rep)
-          case thisLocal: AllocateIOLocalVar =>
-            thisLocal.allocateIO(rawId, rep)
-        }
-      case _: UserTypeInstream =>
+        createSubstreamBuffered(id, knownSizeType.bytes, io, rep, defEndian)
+      case knownSizeType: CalcUserTypeFromBytes =>
+        createSubstreamBuffered(id, knownSizeType.bytes, io, rep, defEndian)
+      case _: UserTypeInstream | _: CalcUserType =>
         // no fixed buffer, just use regular IO
         io
     }