From 764d2b2dcc6efdb57123acae01eb7148883d7ff4 Mon Sep 17 00:00:00 2001
From: Sam Ford <1584702+samford@users.noreply.github.com>
Date: Fri, 13 Jun 2025 18:36:30 -0400
Subject: [PATCH] Add HOMEBREW_MACOS_NEWEST_SUPPORTED env var

We have a `HOMEBREW_MACOS_NEWEST_UNSUPPORTED` environment variable
and this is used in `MacOSVersion` to determine prerelease versions
but we don't have a way of easily determining the newest supported
macOS version.

`bump-cask-pr` contains logic that assumes the first key/value in
`MacOSVersion::SYMBOLS` is the newest macOS version but it recently
became clear that this is a prerelease version between WWDC and the
subsequent macOS release. Similarly, `dev-cmd/generate-cask-api.rb`
tries to compute the newest stable macOS version as
`HOMEBREW_MACOS_NEWEST_UNSUPPORTED.to_i - 1` and this will fail
if/when we update that variable to `"26"`, as the macOS version
before 26 is 15, not 25.

This adds a `HOMEBREW_MACOS_NEWEST_SUPPORTED` environment variable,
so we have a straightforward way of quickly identifying the newest
supported macOS version without having to make potentially unreliable
assumptions or do computations to identify the latest non-prerelease
`MacOSVersion` value. This also updates the two aforementioned areas
to use this environment variable to produce the newest stable macOS
version symbol in a more reliable way.
---
 Library/Homebrew/brew.sh                           | 3 +++
 Library/Homebrew/dev-cmd/bump-cask-pr.rb           | 2 +-
 Library/Homebrew/dev-cmd/generate-cask-api.rb      | 2 +-
 Library/Homebrew/global.rb                         | 1 +
 Library/Homebrew/test/dev-cmd/bump-cask-pr_spec.rb | 2 +-
 5 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Library/Homebrew/brew.sh b/Library/Homebrew/brew.sh
index 537ee55a4e..3557d8a40b 100644
--- a/Library/Homebrew/brew.sh
+++ b/Library/Homebrew/brew.sh
@@ -614,6 +614,8 @@ esac
 # and, if needed:
 # - MacOSVersion::SYMBOLS
 HOMEBREW_MACOS_NEWEST_UNSUPPORTED="16"
+# TODO: bump version when new macOS is released
+HOMEBREW_MACOS_NEWEST_SUPPORTED="15"
 # TODO: bump version when new macOS is released and update references in:
 # - docs/Installation.md
 # - HOMEBREW_MACOS_OLDEST_SUPPORTED in .github/workflows/pkg-installer.yml
@@ -841,6 +843,7 @@ export HOMEBREW_OS_VERSION
 export HOMEBREW_MACOS_VERSION
 export HOMEBREW_MACOS_VERSION_NUMERIC
 export HOMEBREW_MACOS_NEWEST_UNSUPPORTED
+export HOMEBREW_MACOS_NEWEST_SUPPORTED
 export HOMEBREW_MACOS_OLDEST_SUPPORTED
 export HOMEBREW_MACOS_OLDEST_ALLOWED
 export HOMEBREW_USER_AGENT
diff --git a/Library/Homebrew/dev-cmd/bump-cask-pr.rb b/Library/Homebrew/dev-cmd/bump-cask-pr.rb
index 72e20c132e..e7ce29cc99 100644
--- a/Library/Homebrew/dev-cmd/bump-cask-pr.rb
+++ b/Library/Homebrew/dev-cmd/bump-cask-pr.rb
@@ -190,7 +190,7 @@ module Homebrew
       def generate_system_options(cask)
         current_os = Homebrew::SimulateSystem.current_os
         current_os_is_macos = MacOSVersion::SYMBOLS.include?(current_os)
-        newest_macos = MacOSVersion::SYMBOLS.keys.first
+        newest_macos = MacOSVersion.new(HOMEBREW_MACOS_NEWEST_SUPPORTED).to_sym
 
         depends_on_archs = cask.depends_on.arch&.filter_map { |arch| arch[:type] }&.uniq
 
diff --git a/Library/Homebrew/dev-cmd/generate-cask-api.rb b/Library/Homebrew/dev-cmd/generate-cask-api.rb
index 9f639aec52..11922c7212 100644
--- a/Library/Homebrew/dev-cmd/generate-cask-api.rb
+++ b/Library/Homebrew/dev-cmd/generate-cask-api.rb
@@ -45,7 +45,7 @@ module Homebrew
           Cask::Cask.generating_hash!
 
           all_casks = {}
-          latest_macos = MacOSVersion.new((HOMEBREW_MACOS_NEWEST_UNSUPPORTED.to_i - 1).to_s).to_sym
+          latest_macos = MacOSVersion.new(HOMEBREW_MACOS_NEWEST_SUPPORTED).to_sym
           Homebrew::SimulateSystem.with(os: latest_macos, arch: :arm) do
             tap.cask_files.each do |path|
               cask = Cask::CaskLoader.load(path)
diff --git a/Library/Homebrew/global.rb b/Library/Homebrew/global.rb
index ff9d0f79b3..46dac9b308 100644
--- a/Library/Homebrew/global.rb
+++ b/Library/Homebrew/global.rb
@@ -51,6 +51,7 @@ HOMEBREW_HOME_PLACEHOLDER = "/$HOME"
 HOMEBREW_CASK_APPDIR_PLACEHOLDER = "$APPDIR"
 
 HOMEBREW_MACOS_NEWEST_UNSUPPORTED = ENV.fetch("HOMEBREW_MACOS_NEWEST_UNSUPPORTED").freeze
+HOMEBREW_MACOS_NEWEST_SUPPORTED = ENV.fetch("HOMEBREW_MACOS_NEWEST_SUPPORTED").freeze
 HOMEBREW_MACOS_OLDEST_SUPPORTED = ENV.fetch("HOMEBREW_MACOS_OLDEST_SUPPORTED").freeze
 HOMEBREW_MACOS_OLDEST_ALLOWED = ENV.fetch("HOMEBREW_MACOS_OLDEST_ALLOWED").freeze
 
diff --git a/Library/Homebrew/test/dev-cmd/bump-cask-pr_spec.rb b/Library/Homebrew/test/dev-cmd/bump-cask-pr_spec.rb
index 2152491e82..5d78ee310f 100644
--- a/Library/Homebrew/test/dev-cmd/bump-cask-pr_spec.rb
+++ b/Library/Homebrew/test/dev-cmd/bump-cask-pr_spec.rb
@@ -6,7 +6,7 @@ require "dev-cmd/bump-cask-pr"
 RSpec.describe Homebrew::DevCmd::BumpCaskPr do
   subject(:bump_cask_pr) { described_class.new(["test"]) }
 
-  let(:newest_macos) { MacOSVersion::SYMBOLS.keys.first }
+  let(:newest_macos) { MacOSVersion.new(HOMEBREW_MACOS_NEWEST_SUPPORTED).to_sym }
 
   let(:c) do
     Cask::Cask.new("test") do