fixes #25693 (#25842)

(cherry picked from commit 7813bd8b92)

compiler/sigmatch.nim

@@ -2474,6 +2474,10 @@ proc paramTypesMatchAux(m: var TCandidate, f, a: PType,
       return arg
     elif f.kind == tyStatic and arg.typ.n != nil:
       return arg.typ.n
+    elif f.kind == tyUntyped:
+      # bug #25693: a different overload candidate may have sem-checked the
+      # operand and left symbols behind; templates expect the pristine AST.
+      return argOrig
     else:
       return argSemantized # argOrig
 

tests/template/toverload_over_untyped.nim

@@ -0,0 +1,32 @@
+discard """
+  output: "ok"
+"""
+
+# bug #25693
+
+template g(b: untyped) {.dirty.} =
+  template t: untyped = b
+
+proc d() = discard @[0]
+proc g(_: int) = discard
+
+proc f(a: var seq[int], _: string) =
+  let p = @[0]
+  d()
+  a = p
+
+let q = "a"
+g:
+  var a: seq[int]
+  try:
+    f(a, q & "1")
+  except CatchableError:
+    discard
+  try:
+    f(a, q & "1")
+  except CatchableError:
+    discard
+block: t()
+block: t()
+echo "ok"
+