fix #19349 incompatible type when mixing float32 and cfloat in generics (#20551)

(cherry picked from commit 84fab7f39b)

compiler/types.nim

@@ -1145,13 +1145,14 @@ proc sameTypeAux(x, y: PType, c: var TSameTypeClosure): bool =
   of tyEmpty, tyChar, tyBool, tyNil, tyPointer, tyString, tyCstring,
      tyInt..tyUInt64, tyTyped, tyUntyped, tyVoid:
     result = sameFlags(a, b)
-    if result and PickyCAliases in c.flags:
+    if result and {PickyCAliases, ExactTypeDescValues} <= c.flags:
       # additional requirement for the caching of generics for importc'ed types:
       # the symbols must be identical too:
       let symFlagsA = if a.sym != nil: a.sym.flags else: {}
       let symFlagsB = if b.sym != nil: b.sym.flags else: {}
       if (symFlagsA+symFlagsB) * {sfImportc, sfExportc} != {}:
         result = symFlagsA == symFlagsB
+
   of tyStatic, tyFromExpr:
     result = exprStructuralEquivalent(a.n, b.n) and sameFlags(a, b)
     if result and a.len == b.len and a.len == 1:

tests/alias/t19349.nim

@@ -0,0 +1,19 @@
+discard """
+  action: "compile"
+"""
+
+type
+  Vec3[T: SomeNumber] = object
+    arr: array[3, T]
+
+var 
+  cfloatArr: array[3, array[3, cfloat]]
+  cfloatSeq = newSeq[Vec3[cfloat]]()
+for row in cfloatArr:
+  cfloatSeq.add(Vec3[float32](arr: [row[0], row[1], row[2]]))
+
+var 
+  cuintArr: array[3, array[3, cuint]]
+  cuintSeq = newSeq[Vec3[cuint]]()
+for row in cuintArr:
+  cuintSeq.add(Vec3[uint32](arr: [row[0], row[1], row[2]]))