attestation: remove gh version detection

I'm declaring bankruptcy on this entire approach:

1. We can attempt to match on versions, but this will fail
   when the version of `gh` installed is built from `HEAD`
   or similar.
2. We can match on dates instead (since `gh --version` also includes
   the date), but this is even more brittle + implies a support
   contract we don't actually have (we don't actually want
   to say we support random dated builds between public releases
   of `gh`).

This moves us back to a simpler approach: if `gh` is present,
we use it. If `gh` is not present, we attempt to install it
with `ensure_executable!`. If the user's `gh` is present but too old,
it'll fail during attestation verification with a reasonable error,
which IMO is fine for now since this is all still in beta.

Signed-off-by: William Woodruff <william@yossarian.net>

Library/Homebrew/attestation.rb

@@ -15,9 +15,6 @@ module Homebrew
     # @api private
     HOMEBREW_CORE_REPO = "Homebrew/homebrew-core"
 
-    # @api private
-    GH_ATTESTATION_MIN_VERSION = T.let(Version.new("2.49.0").freeze, Version)
-
     # @api private
     BACKFILL_REPO = "trailofbits/homebrew-brew-verify"
 
@@ -74,25 +71,14 @@ module Homebrew
     # @api private
     sig { returns(Pathname) }
     def self.gh_executable
-      # NOTE: We set HOMEBREW_NO_VERIFY_ATTESTATIONS when installing `gh` itself,
-      #       to prevent a cycle during bootstrapping. This can eventually be resolved
-      #       by vendoring a pure-Ruby Sigstore verifier client.
       @gh_executable ||= T.let(nil, T.nilable(Pathname))
       return @gh_executable if @gh_executable.present?
 
+      # NOTE: We set HOMEBREW_NO_VERIFY_ATTESTATIONS when installing `gh` itself,
+      #       to prevent a cycle during bootstrapping. This can eventually be resolved
+      #       by vendoring a pure-Ruby Sigstore verifier client.
       with_env(HOMEBREW_NO_VERIFY_ATTESTATIONS: "1") do
-        @gh_executable = ensure_executable!("gh", reason: "verifying attestations")
+        @gh_executable = ensure_executable!("gh", reason: "verifying attestations", latest: true)
-
-        gh_version = Version.new(system_command!(@gh_executable, args: ["--version"], print_stderr: false)
-                                 .stdout.match(/\d+(?:\.\d+)+/i).to_s)
-        if gh_version < GH_ATTESTATION_MIN_VERSION
-          if Formula["gh"].version < GH_ATTESTATION_MIN_VERSION
-            raise "#{@gh_executable} is too old, you must upgrade it to >=#{GH_ATTESTATION_MIN_VERSION} to continue"
-          end
-
-          @gh_executable = ensure_formula_installed!("gh", latest: true,
-                                                           reason: "verifying attestations").opt_bin/"gh"
-        end
       end
 
       T.must(@gh_executable)

Library/Homebrew/extend/kernel.rb

@@ -425,7 +425,7 @@ module Kernel
   end
 
   # Ensure the given executable is exist otherwise install the brewed version
-  def ensure_executable!(name, formula_name = nil, reason: "")
+  def ensure_executable!(name, formula_name = nil, reason: "", latest: false)
     formula_name ||= name
 
     executable = [

Library/Homebrew/test/attestation_spec.rb

@@ -6,9 +6,6 @@ RSpec.describe Homebrew::Attestation do
   let(:fake_gh) { Pathname.new("/extremely/fake/gh") }
   let(:fake_old_gh) { Pathname.new("/extremely/fake/old/gh") }
   let(:fake_gh_creds) { "fake-gh-api-token" }
-  let(:fake_gh_formula) { instance_double(Formula, "gh", opt_bin: Pathname.new("/extremely/fake")) }
-  let(:fake_gh_version) { instance_double(SystemCommand::Result, stdout: "2.49.0") }
-  let(:fake_old_gh_version) { instance_double(SystemCommand::Result, stdout: "2.48.0") }
   let(:fake_error_status) { instance_double(Process::Status, exitstatus: 1, termsig: nil) }
   let(:fake_auth_status) { instance_double(Process::Status, exitstatus: 4, termsig: nil) }
   let(:cached_download) { "/fake/cached/download" }
@@ -69,24 +66,10 @@ RSpec.describe Homebrew::Attestation do
   end
 
   describe "::gh_executable" do
-    before do
+    it "calls ensure_executable" do
-      allow(Formulary).to receive(:factory)
-        .with("gh")
-        .and_return(instance_double(Formula, version: Version.new("2.49.0")))
-
-      allow(described_class).to receive(:system_command!)
-        .with(fake_old_gh, args: ["--version"], print_stderr: false)
-        .and_return(fake_old_gh_version)
-    end
-
-    it "calls ensure_executable and ensure_formula_installed" do
       expect(described_class).to receive(:ensure_executable!)
-        .with("gh", reason: "verifying attestations")
+        .with("gh", reason: "verifying attestations", latest: true)
-        .and_return(fake_old_gh)
+        .and_return(fake_gh)
-
-      expect(described_class).to receive(:ensure_formula_installed!)
-        .with("gh", latest: true, reason: "verifying attestations")
-        .and_return(fake_gh_formula)
 
       described_class.gh_executable
     end