Add heroku-26 stack support (heroku#1727)

* Default ruby_url to arch-aware path for future stacks

Invert the if/else in download_ruby so heroku-22 (amd64-only) is the
special case and all other stacks default to the arch-aware binary
path ($stack/$arch/ruby-$version.tgz). This means future stacks
automatically get multi-arch bootstrap ruby downloads without needing
a code change here.

Previously every new multi-arch stack had to be added to the if-check.
Now only legacy amd64-only stacks need to be listed.

This is a pure refactor with no behavior change.

* Refactor MULTI_ARCH_STACKS to AMD_ONLY_STACKS

Invert the Ruby-side multi-arch stack logic so that heroku-22
(amd64-only) is the special case and all other stacks default to
arch-aware binary paths. This means future stacks automatically get
multi-arch support without code changes.

Previously, every new multi-arch stack had to be added to
MULTI_ARCH_STACKS. Now only legacy amd64-only stacks need to be listed
in AMD_ONLY_STACKS.

Renamed across source and specs:
- MULTI_ARCH_STACKS -> AMD_ONLY_STACKS (base.rb)
- multi_arch_stacks: param -> amd_only_stacks: (download_presence.rb,
  heroku_ruby_installer.rb, ruby.rb)

This is a pure refactor with no behavior change.

* Add heroku-26 to supported stacks

Add heroku-26 to the checks::ensure_supported_stack case statement
in bash_functions.sh and add a unit test verifying it passes
validation.

* Add heroku-26 to download presence stacks

Add heroku-26 to DownloadPresence::STACKS so the buildpack can check
Ruby binary availability on heroku-26 and warn users upgrading stacks
if their Ruby version is not available on the next stack.

- download_presence.rb: Add heroku-26 to STACKS
- download_presence_spec.rb: Update "files that do not exist" test to
  use heroku-24/heroku-26 pair (as the old test's comment requested),
  add test verifying next_stack from heroku-24 is heroku-26

* Add pending heroku-26 integration test

Deploy Ruby 3.3.10 on heroku-26 using the default_ruby fixture.
Marked pending until heroku-26 is available on the platform

```
$ heroku stack:set heroku-26
Setting stack to heroku-26... !
 ›   Error: You can't switch to heroku-26. Available options: container, heroku-22, heroku-24.
 ›
 ›   Error ID: unsupported
```

The job fails with 422

```
Pending: (Failures listed here are expected and do not affect your suite's status)

  1) Ruby on heroku-26 deploys Ruby 3.3.10
     # heroku-26 not yet available on the platform
     Failure/Error:
       app.deploy do |app|
         expect(app.run("command -v ruby").strip).to eq("/app/bin/ruby")
       end

     Excon::Error::UnprocessableEntity:
       Expected([200, 201, 202, 204, 206, 304, 429]) <=> Actual(422 Unprocessable Entity)
     # /Users/rschneeman/.gem/ruby/3.3.9/gems/excon-1.4.0/lib/excon/middlewares/expects.rb:13:in `response_call'
     # /Users/rschneeman/.gem/ruby/3.3.9/gems/excon-1.4.0/lib/excon/middlewares/decompress.rb:35:in `response_call'
```

Author: schneems

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Add heroku-26 stack support
 
 ## [v352] - 2026-03-16
 

bin/support/bash_functions.sh

@@ -169,7 +169,7 @@ function checks::ensure_supported_stack() {
 
 	case "${stack}" in
 		# When removing support from a stack, move it to the bottom of the list
-		heroku-22 | heroku-24)
+		heroku-22 | heroku-24 | heroku-26)
 			return 0
 			;;
 		heroku-18 | heroku-20)

bin/support/download_ruby

@@ -29,12 +29,12 @@ ruby_url() {
   local stack=$1
   local version=$2
 
-  if [ "$stack" == "heroku-24" ]; then
+  if [ "$stack" == "heroku-22" ]; then
+    echo "${BUILDPACK_VENDOR_URL:-https://heroku-buildpack-ruby.s3.dualstack.us-east-1.amazonaws.com}/$stack/ruby-$version.tgz"
+  else
     local arch
     arch=$(dpkg --print-architecture)
     echo "${BUILDPACK_VENDOR_URL:-https://heroku-buildpack-ruby.s3.dualstack.us-east-1.amazonaws.com}/$stack/$arch/ruby-$version.tgz"
-  else
-    echo "${BUILDPACK_VENDOR_URL:-https://heroku-buildpack-ruby.s3.dualstack.us-east-1.amazonaws.com}/$stack/ruby-$version.tgz"
   fi
 }
 

lib/language_pack/base.rb

@@ -17,7 +17,7 @@ class LanguagePack::Base
 
   VENDOR_URL = ENV["BUILDPACK_VENDOR_URL"] || "https://heroku-buildpack-ruby.s3.dualstack.us-east-1.amazonaws.com"
   ROOT_DIR = File.expand_path("../../..", __FILE__)
-  MULTI_ARCH_STACKS = ["heroku-24"]
+  AMD_ONLY_STACKS = ["heroku-22"]
   KNOWN_ARCHITECTURES = ["amd64", "arm64"]
 
   attr_reader :app_path, :bundler, :cache, :environment_name, :stack

lib/language_pack/helpers/download_presence.rb

@@ -8,27 +8,27 @@
 #
 #    download = LanguagePack::Helpers::DownloadPresence.new(
 #      'ruby-3.1.7.tgz',
-#      stacks: ['heroku-22', 'heroku-24']
+#      stacks: ['heroku-22', 'heroku-24', 'heroku-26']
 #    )
 #
 #    download.call
 #
 #    puts download.exists? #=> true
-#    puts download.valid_stack_list #=> ['heroku-22', 'heroku-24']
+#    puts download.valid_stack_list #=> ['heroku-22', 'heroku-24', 'heroku-26']
 class LanguagePack::Helpers::DownloadPresence
-  # heroku-22 and heroku-24 have identical ruby versions supported
-  STACKS = ["heroku-22", "heroku-24"]
+  # heroku-22, heroku-24, and heroku-26 have identical ruby versions supported
+  STACKS = ["heroku-22", "heroku-24", "heroku-26"]
 
-  def initialize(file_name:, arch:, multi_arch_stacks:, stacks: STACKS)
+  def initialize(file_name:, arch:, amd_only_stacks:, stacks: STACKS)
     @file_name = file_name
     @stacks = stacks
     @fetchers = []
     @threads = []
     @stacks.each do |stack|
-      @fetchers << if multi_arch_stacks.include?(stack)
-        LanguagePack::Fetcher.new(LanguagePack::Base::VENDOR_URL, stack: stack, arch: arch)
-      else
+      @fetchers << if amd_only_stacks.include?(stack)
         LanguagePack::Fetcher.new(LanguagePack::Base::VENDOR_URL, stack: stack)
+      else
+        LanguagePack::Fetcher.new(LanguagePack::Base::VENDOR_URL, stack: stack, arch: arch)
       end
     end
   end

lib/language_pack/installers/heroku_ruby_installer.rb

@@ -10,18 +10,18 @@ class LanguagePack::Installers::HerokuRubyInstaller
 
   attr_reader :fetcher, :environment
 
-  def initialize(stack:, multi_arch_stacks:, arch:, app_path:, env:, report: HerokuBuildReport::GLOBAL)
+  def initialize(stack:, amd_only_stacks:, arch:, app_path:, env:, report: HerokuBuildReport::GLOBAL)
     @report = report
     @environment = env
     @app_path = Pathname.new(app_path).expand_path
-    @fetcher = self.class.fetcher(multi_arch_stacks: multi_arch_stacks, stack: stack, arch: arch)
+    @fetcher = self.class.fetcher(amd_only_stacks: amd_only_stacks, stack: stack, arch: arch)
   end
 
-  def self.fetcher(multi_arch_stacks:, stack:, arch:)
-    if multi_arch_stacks.include?(stack)
-      LanguagePack::Fetcher.new(BASE_URL, stack: stack, arch: arch)
-    else
+  def self.fetcher(amd_only_stacks:, stack:, arch:)
+    if amd_only_stacks.include?(stack)
       LanguagePack::Fetcher.new(BASE_URL, stack: stack)
+    else
+      LanguagePack::Fetcher.new(BASE_URL, stack: stack, arch: arch)
     end
   end
 

lib/language_pack/ruby.rb

@@ -79,7 +79,7 @@ def best_practice_warnings
   def compile
     @outdated_version_check = LanguagePack::Helpers::OutdatedRubyVersion.new(
       current_ruby_version: ruby_version,
-      fetcher: LanguagePack::Installers::HerokuRubyInstaller.fetcher(multi_arch_stacks: MULTI_ARCH_STACKS, stack: stack, arch: @arch)
+      fetcher: LanguagePack::Installers::HerokuRubyInstaller.fetcher(amd_only_stacks: AMD_ONLY_STACKS, stack: stack, arch: @arch)
     ).call
 
     @warn_io.warnings.each { |warning| warnings << warning }
@@ -477,15 +477,15 @@ def self.install_ruby(app_path:, ruby_version:, stack:, arch:, metadata:, io:)
     return false unless ruby_version
 
     installer = LanguagePack::Installers::HerokuRubyInstaller.new(
-      multi_arch_stacks: MULTI_ARCH_STACKS,
+      amd_only_stacks: AMD_ONLY_STACKS,
       stack: stack,
       arch: arch,
       app_path: app_path,
       env: ENV
     )
 
     @ruby_download_check = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: MULTI_ARCH_STACKS,
+      amd_only_stacks: AMD_ONLY_STACKS,
       file_name: ruby_version.file_name,
       arch: arch
     )

lib/language_pack/test/ruby.rb

@@ -7,7 +7,7 @@ class LanguagePack::Ruby
   def compile
     @outdated_version_check = LanguagePack::Helpers::OutdatedRubyVersion.new(
       current_ruby_version: ruby_version,
-      fetcher: LanguagePack::Installers::HerokuRubyInstaller.fetcher(multi_arch_stacks: MULTI_ARCH_STACKS, stack: stack, arch: @arch)
+      fetcher: LanguagePack::Installers::HerokuRubyInstaller.fetcher(amd_only_stacks: AMD_ONLY_STACKS, stack: stack, arch: @arch)
     ).call
     @warn_io.warnings.each { |warning| warnings << warning }
     post_bundler(ruby_version: @ruby_version, app_path: app_path)

spec/hatchet/rubies_spec.rb

@@ -48,6 +48,21 @@
   end
 end
 
+describe "Ruby on heroku-26" do
+  it "deploys Ruby 3.3.10" do
+    pending("heroku-26 not yet available on the platform")
+    Hatchet::Runner.new("default_ruby", stack: "heroku-26").tap do |app|
+      app.before_deploy do
+        set_ruby_version(version: "3.3.10")
+      end
+
+      app.deploy do |app|
+        expect(app.run("command -v ruby").strip).to eq("/app/bin/ruby")
+      end
+    end
+  end
+end
+
 describe "Upgrading ruby apps" do
   it "works when changing versions" do
     version = "3.3.1"

spec/helpers/download_presence_spec.rb

@@ -3,7 +3,7 @@
 describe LanguagePack::Helpers::DownloadPresence do
   it "handles multi-arch transitions for files that exist" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: ["heroku-24"],
+      amd_only_stacks: ["heroku-22"],
       file_name: "ruby-3.1.4.tgz",
       stacks: ["heroku-22", "heroku-24"],
       arch: "amd64"
@@ -19,26 +19,23 @@
 
   it "handles multi-arch transitions for files that do not exist" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: ["heroku-24"],
+      amd_only_stacks: [],
       file_name: "ruby-3.0.5.tgz",
-      # Heroku 20 is not longer supported however heroku-22 and heroku-24
-      # have identical Ruby versions supported, this test can be updated to
-      # use heroku-24 and heroku-26 (when that stack is released)
-      stacks: ["heroku-20", "heroku-24"],
+      stacks: ["heroku-24", "heroku-26"],
       arch: "amd64"
     )
 
     download.call
 
-    expect(download.next_stack(current_stack: "heroku-20")).to eq("heroku-24")
-    expect(download.next_stack(current_stack: "heroku-24")).to be_falsey
+    expect(download.next_stack(current_stack: "heroku-24")).to eq("heroku-26")
+    expect(download.next_stack(current_stack: "heroku-26")).to be_falsey
 
-    expect(download.exists_on_next_stack?(current_stack: "heroku-20")).to be_falsey
+    expect(download.exists_on_next_stack?(current_stack: "heroku-24")).to be_falsey
   end
 
   it "knows if exists on the next stack" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: ["heroku-24"],
+      amd_only_stacks: ["heroku-22"],
       file_name: "#{LanguagePack::RubyVersion::DEFAULT_VERSION}.tgz",
       stacks: ["heroku-22", "heroku-24"],
       arch: "amd64"
@@ -54,7 +51,7 @@
 
   it "detects when a package is present on two stacks but not a third" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: [],
+      amd_only_stacks: ["cedar-14", "heroku-16", "heroku-18"],
       file_name: "ruby-2.3.0.tgz",
       stacks: ["cedar-14", "heroku-16", "heroku-18"],
       arch: nil
@@ -68,7 +65,7 @@
 
   it "detects when a package does not exist" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: [],
+      amd_only_stacks: ["heroku-22"],
       file_name: "does-not-exist.tgz",
       stacks: ["heroku-22", "heroku-24"],
       arch: nil
@@ -82,20 +79,32 @@
 
   it "detects default ruby version" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: ["heroku-24"],
+      amd_only_stacks: LanguagePack::Base::AMD_ONLY_STACKS,
       file_name: "#{LanguagePack::RubyVersion::DEFAULT_VERSION}.tgz",
       arch: "amd64"
     )
 
     download.call
 
     expect(download.exists?).to eq(true)
-    expect(download.valid_stack_list).to include(LanguagePack::Helpers::DownloadPresence::STACKS.last)
+    expect(download.valid_stack_list).to include("heroku-24")
+  end
+
+  it "next stack for ruby 3.0.10 from heroku-24 is heroku-26" do
+    download = LanguagePack::Helpers::DownloadPresence.new(
+      amd_only_stacks: LanguagePack::Base::AMD_ONLY_STACKS,
+      file_name: "ruby-3.0.10.tgz",
+      arch: "amd64"
+    )
+
+    download.call
+
+    expect(download.next_stack(current_stack: "heroku-24")).to eq("heroku-26")
   end
 
   it "handles the current stack not being in the known stacks list" do
     download = LanguagePack::Helpers::DownloadPresence.new(
-      multi_arch_stacks: [],
+      amd_only_stacks: LanguagePack::Base::AMD_ONLY_STACKS,
       file_name: "#{LanguagePack::RubyVersion::DEFAULT_VERSION}.tgz",
       arch: nil
     )