fixes #20715; range[a..b] inside object variant fails (#20716)

* fixes #20715; range[a..b] inside object variant fails

* step one fix

* better fix

* fixes private fields

* mistake

compiler/sem.nim

@@ -599,15 +599,16 @@ proc defaultFieldsForTheUninitialized(c: PContext, recNode: PNode): seq[PNode] =
   of nkRecCase:
     let discriminator = recNode[0]
     var selectedBranch: int
-    let defaultValue = discriminator.sym.ast
+    var defaultValue = discriminator.sym.ast
     if defaultValue == nil:
       # None of the branches were explicitly selected by the user and no value
       # was given to the discrimator. We can assume that it will be initialized
       # to zero and this will select a particular branch as a result:
-      selectedBranch = recNode.pickCaseBranchIndex newIntNode(nkIntLit#[c.graph]#, 0)
-    else: # Try to use default value
-      selectedBranch = recNode.pickCaseBranchIndex defaultValue
-      result.add newTree(nkExprColonExpr, discriminator, defaultValue)
+      defaultValue = newIntNode(nkIntLit#[c.graph]#, 0)
+      defaultValue.typ = discriminator.typ
+    selectedBranch = recNode.pickCaseBranchIndex defaultValue
+    defaultValue.flags.incl nfUseDefaultField
+    result.add newTree(nkExprColonExpr, discriminator, defaultValue)
     result.add defaultFieldsForTheUninitialized(c, recNode[selectedBranch][^1])
   of nkSym:
     let field = recNode.sym

tests/objects/tobject_default_value.nim

@@ -426,6 +426,36 @@ template main {.dirty.} =
     let x = default(A)
     doAssert $x == "(d: Uninitialized DateTime)"
 
+  block: # bug #20715
+    block:
+      type
+        Foo = enum
+          A
+          B
+
+        Bar = object
+          case foo: Foo
+          of A:
+            t: range[-1..2]
+          else: discard
+
+      var d = default(Bar)
+      doAssert d.t == -1
+
+    block:
+      type
+        Foo = enum
+          A
+          B
+
+        Bar = object
+          case foo: Foo
+          of A:
+            t: range[0..2]
+          else: discard
+
+      var d = default(Bar)
+      doAssert d.t == 0
 
 static: main()
 main()