fixes #13646

compiler/semexprs.nim

@@ -232,13 +232,14 @@ proc semConv(c: PContext, n: PNode): PNode =
   result = newNodeI(nkConv, n.info)
 
   var targetType = semTypeNode(c, n[0], nil)
-  if targetType.kind == tyTypeDesc:
+  case targetType.kind
+  of tyTypeDesc:
     internalAssert c.config, targetType.len > 0
     if targetType.base.kind == tyNone:
       return semTypeOf(c, n)
     else:
       targetType = targetType.base
-  elif targetType.kind == tyStatic:
+  of tyStatic:
     var evaluated = semStaticExpr(c, n[1])
     if evaluated.kind == nkType or evaluated.typ.kind == tyTypeDesc:
       result = n
@@ -248,6 +249,7 @@ proc semConv(c: PContext, n: PNode): PNode =
       return evaluated
     else:
       targetType = targetType.base
+  else: discard
 
   maybeLiftType(targetType, c, n[0].info)
 
@@ -268,7 +270,7 @@ proc semConv(c: PContext, n: PNode): PNode =
       targetType.skipTypes(abstractPtrs).kind == tyObject:
     localError(c.config, n.info, "object construction uses ':', not '='")
   var op = semExprWithType(c, n[1])
-  if targetType.isMetaType:
+  if targetType.kind != tyGenericParam and targetType.isMetaType:
     let final = inferWithMetatype(c, targetType, op, true)
     result.add final
     result.typ = final.typ
@@ -279,6 +281,10 @@ proc semConv(c: PContext, n: PNode): PNode =
   # here or needs to be overwritten too then.
   result.add op
 
+  if targetType.kind == tyGenericParam:
+    result.typ = makeTypeFromExpr(c, copyTree(result))
+    return result
+
   if not isSymChoice(op):
     let status = checkConvertible(c, result.typ, op)
     case status

compiler/semtypinst.nim

@@ -618,6 +618,9 @@ proc replaceTypeVarsTAux(cl: var TReplTypeVars, t: PType): PType =
         eraseVoidParams(result)
         skipIntLiteralParams(result)
 
+      of tyRange:
+        result[0] = result[0].skipTypes({tyStatic, tyDistinct})
+
       else: discard
     else:
       # If this type doesn't refer to a generic type we may still want to run it

tests/metatype/tmetatype_various.nim

@@ -1,4 +1,7 @@
-
+discard """
+  output: '''[1, 0, 0, 0, 0, 0, 0, 0]
+ CTBool[Ct[system.uint32]]'''
+"""
 
 block tconstraints:
   proc myGenericProc[T: object|tuple|int|ptr|ref|distinct](x: T): string =
@@ -46,4 +49,20 @@ block tprocbothmeta:
   assert myMap(@[1,2,3], myFun) == @[11.0, 12.0, 13.0]
 
 
+# https://github.com/nim-lang/Nim/issues/13646
+
+type
+  BaseUint* = SomeUnsignedInt or byte
+  Ct*[T] = distinct T
+    ## Constant-Time wrapper
+    ## Only constant-time operations in particular the ternary operator equivalent
+    ##   condition: if true: a else: b
+    ## are allowed
+
+  CTBool*[T] = distinct range[T(0)..T(1)]
+    ## Constant-Time boolean wrapper
+
+var x: array[8, CTBool[Ct[uint32]]]
+x[0] = (CTBool[Ct[uint32]])(1)
+echo x.repr, " ", typeof(x[0])