Autoconf 2.69, needed to install Erlang with BigSur (fails with 2.71)

autoconf.rb

class Autoconf < Formula
  desc "Automatic configure script builder"
  homepage "https://www.gnu.org/software/autoconf"
  url "https://ftp.gnu.org/gnu/autoconf/autoconf-2.69.tar.gz"
  mirror "https://ftpmirror.gnu.org/autoconf/autoconf-2.69.tar.gz"
  sha256 "954bd69b391edc12d6a4a51a2dd1476543da5c6bbf05a95b59dc0dd6fd4c2969"
  license all_of: [
    "GPL-3.0-or-later",
    "GPL-3.0-or-later" => { with: "Autoconf-exception-3.0" },
  ]

  bottle do
    sha256 cellar: :any_skip_relocation, arm64_big_sur: "6279cc6294da77a87b2e08783f39a97e8678bde9b3e2899685879cabee6d2945"
  end

  depends_on "m4"
  uses_from_macos "perl"

  def install
    on_macos do
      ENV["PERL"] = "/usr/bin/perl"

      # force autoreconf to look for and use our glibtoolize
      inreplace "bin/autoreconf.in", "libtoolize", "glibtoolize"
      # also touch the man page so that it isn't rebuilt
      inreplace "man/autoreconf.1", "libtoolize", "glibtoolize"
    end

    system "./configure", "--prefix=#{prefix}", "--with-lispdir=#{elisp}"
    system "make", "install"

    rm_f info/"standards.info"
  end

  test do
    cp pkgshare/"autotest/autotest.m4", "autotest.m4"
    system bin/"autoconf", "autotest.m4"

    (testpath/"configure.ac").write <<~EOS
      AC_INIT([hello], [1.0])
      AC_CONFIG_SRCDIR([hello.c])
      AC_PROG_CC
      AC_OUTPUT
    EOS
    (testpath/"hello.c").write "int foo(void) { return 42; }"

    system bin/"autoconf"
    system "./configure"
    assert_predicate testpath/"config.status", :exist?
    assert_match(/\nCC=.*#{ENV.cc}/, (testpath/"config.log").read)
  end
end

install.txt

wget https://gist.githubusercontent.com/oriolgual/2f881fa3a151dd5f643f755ddcf2a0bc/raw/f4866d7362491492fd944c240d89387762147cd3/autoconf.rb
brew uninstall autoconf --ignore-dependencies
brew install ./autoconf.rb

Error: Failed to load cask: ./autoconf.rb
Cask 'autoconf' is unreadable: wrong constant name #Class:0x0000000117188a40
Warning: Treating ./autoconf.rb as a formula.
==> Fetching autoconf
==> Downloading https://ghcr.io/v2/homebrew/core/autoconf/manifests/2.69
Error: autoconf: Failed to download resource "autoconf_bottle_manifest"
...
curl: (22) The requested URL returned error: 404

This simpler solution works for me:

$ brew uninstall autoconf
$ brew install autoconf@2.69
$ echo 'export PATH="/opt/homebrew/opt/autoconf@2.69/bin:$PATH"' >> ~/.zshrc