fixes #6972

compiler/renderer.nim

@@ -719,6 +719,7 @@ proc gcase(g: var TSrcGen, n: PNode) =
   var c: TContext
   initContext(c)
   var length = sonsLen(n)
+  if length == 0: return
   var last = if n.sons[length-1].kind == nkElse: -2 else: -1
   if longMode(g, n, 0, last): incl(c.flags, rfLongMode)
   putWithSpace(g, tkCase, "case")

compiler/sem.nim

@@ -74,7 +74,7 @@ proc fitNode(c: PContext, formal: PType, arg: PNode; info: TLineInfo): PNode =
     localError(arg.info, errExprXHasNoType,
                renderTree(arg, {renderNoComments}))
     # error correction:
-    result = copyNode(arg)
+    result = copyTree(arg)
     result.typ = formal
   else:
     result = indexTypesMatch(c, formal, arg.typ, arg)
@@ -168,9 +168,9 @@ proc commonType*(x, y: PType): PType =
 proc endsInNoReturn(n: PNode): bool =
   # check if expr ends in raise exception or call of noreturn proc
   var it = n
-  while it.kind in {nkStmtList, nkStmtListExpr} and it.len > 0: 
+  while it.kind in {nkStmtList, nkStmtListExpr} and it.len > 0:
     it = it.lastSon
-  result = it.kind == nkRaiseStmt or 
+  result = it.kind == nkRaiseStmt or
     it.kind in nkCallKinds and it[0].kind == nkSym and sfNoReturn in it[0].sym.flags
 
 proc commonType*(x: PType, y: PNode): PType =