Fix #25883 tuple sighash collision

compiler/sighashes.nim

@@ -211,6 +211,7 @@ proc hashType(c: var MD5Context, t: PType; flags: set[ConsiderFlag]; conf: Confi
     c.hashTree(t.n, {}, conf)
   of tyTuple:
     c &= char(t.kind)
+    c &= t.len
     if t.n != nil and CoType notin flags:
       for i in 0..<t.n.len:
         assert(t.n[i].kind == nkSym)

tests/ccgbugs2/t25883_tuple_sighash_collision.nim

@@ -0,0 +1,18 @@
+discard """
+output: "5"
+"""
+
+# bug #25883: C codegen assigns same type hash to tuples with different nesting
+# but identical flattened content.
+# ((Int[1], Int[2]), Int[13], Int[14]) and ((Int[1], Int[2], Int[13]), Int[14])
+# must get distinct C type names.
+
+type
+  Int[V: static int] = object
+
+proc main() =
+  var b = ((1, 2), 13, 14)
+  var c = ((1, 2, 13), 14)
+  echo c[0][2]
+
+main()