fixes tcompiletimerange [bugfix] (#11720)

compiler/semtypes.nim

@@ -1379,8 +1379,11 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
   if tx.isNil or isTupleRecursive(tx):
     localError(c.config, n.info, "illegal recursion in type '$1'" % typeToString(result[0]))
     return errorType(c)
-  if tx != result and tx.kind == tyObject and tx.sons[0] != nil:
-    semObjectTypeForInheritedGenericInst(c, n, tx)
+  if tx != result and tx.kind == tyObject:
+    if tx.sons[0] != nil:
+      semObjectTypeForInheritedGenericInst(c, n, tx)
+    var position = 0
+    recomputeFieldPositions(tx, tx.n, position)
 
 proc maybeAliasType(c: PContext; typeExpr, prev: PType): PType =
   if typeExpr.kind in {tyObject, tyEnum, tyDistinct, tyForward} and prev != nil:

compiler/semtypinst.nim

@@ -667,6 +667,22 @@ proc replaceTypesForLambda*(p: PContext, pt: TIdTable, n: PNode;
   result = replaceTypeVarsN(cl, n)
   popInfoContext(p.config)
 
+proc recomputeFieldPositions*(t: PType; obj: PNode; currPosition: var int) =
+  if t != nil and t.len > 0 and t.sons[0] != nil:
+    let b = skipTypes(t.sons[0], skipPtrs)
+    recomputeFieldPositions(b, b.n, currPosition)
+  case obj.kind
+  of nkRecList:
+    for i in 0 ..< sonsLen(obj): recomputeFieldPositions(nil, obj.sons[i], currPosition)
+  of nkRecCase:
+    recomputeFieldPositions(nil, obj.sons[0], currPosition)
+    for i in 1 ..< sonsLen(obj):
+      recomputeFieldPositions(nil, lastSon(obj.sons[i]), currPosition)
+  of nkSym:
+    obj.sym.position = currPosition
+    inc currPosition
+  else: discard "cannot happen"
+
 proc generateTypeInstance*(p: PContext, pt: TIdTable, info: TLineInfo,
                            t: PType): PType =
   var typeMap = initLayeredTypeMap(pt)
@@ -674,6 +690,10 @@ proc generateTypeInstance*(p: PContext, pt: TIdTable, info: TLineInfo,
   pushInfoContext(p.config, info)
   result = replaceTypeVarsT(cl, t)
   popInfoContext(p.config)
+  let objType = result.skipTypes(abstractInst)
+  if objType.kind == tyObject:
+    var position = 0
+    recomputeFieldPositions(objType, objType.n, position)
 
 proc prepareMetatypeForSigmatch*(p: PContext, pt: TIdTable, info: TLineInfo,
                                  t: PType): PType =

tests/vm/tcompiletimerange.nim

@@ -1,18 +1,17 @@
 discard """
-  disabled: "true"
 """
 
 # issue #8199
 
-const rangesGCHoldEnabled = not defined(rangesDisableGCHold)
+const rangesGCHoldEnabled = true # not defined(rangesDisableGCHold)
 
 type
   # A view into immutable array
   Range*[T] {.shallow.} = object
     when rangesGCHoldEnabled:
-      gcHold: seq[T]
-    start: ptr T
-    mLen: int32
+      gcHold: seq[T] # 0
+    start: ptr T # 1
+    mLen: int32 # 2
 
 type
   BytesRange* = Range[byte]