Ruby version installation errors and warnings

Currently when a customer tries to upgrade their stack and are using an old version of Ruby they get a very unhelpful error: ``` Command: 'set -o pipefail; curl -L --fail --retry 5 --retry-delay 1 --connect-timeout 3 --max-time 30 https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/heroku-18/ruby-1.9.3.tgz -s -o - | tar zxf - ' failed on attempt 1 of 3. Command: 'set -o pipefail; curl -L --fail --retry 5 --retry-delay 1 --connect-timeout 3 --max-time 30 https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/heroku-18/ruby-1.9.3.tgz -s -o - | tar zxf - ' failed on attempt 2 of 3. ! ! An error occurred while installing ruby-1.9.3 ! ! Heroku recommends you use the latest supported Ruby version listed here: ! https://devcenter.heroku.com/articles/ruby-support#supported-runtimes ! ! For more information on syntax for declaring a Ruby version see: ! https://devcenter.heroku.com/articles/ruby-versions ! ! ! Debug InformationCommand: 'set -o pipefail; curl -L --fail --retry 5 --retry-delay 1 --connect-timeout 3 --max-time 30 https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/heroku-18/ruby-1.9.3.tgz -s -o - | tar zxf - ' failed unexpectedly: ! ! gzip: stdin: unexpected end of file ! tar: Child returned status 1 ! tar: Error is not recoverable: exiting now ! ! Push rejected, failed to compile Ruby app. ! Push failed ``` This is awful and gives no context. The goal of this PR is to do a few things: - If a Ruby version does not exist on any stack, explicitly state the problem - If a Ruby version exists, but not on your current stack, list the stacks it is present on - If a Ruby version exists, but not for the next stack (i.e. heroku-16 if you're deploying to cedar-14) then the customer should get a warning
heroku · Feb 26, 2020 · 643d408 · 643d408
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## Master (unreleased)
 
+* Improve Ruby version download error messages (https://github.com/heroku/heroku-buildpack-ruby/pull/953)
 * Update default Ruby version to 2.6.5 (https://github.com/heroku/heroku-buildpack-ruby/pull/947)
 
 ## v207 (12/16/2019)

diff --git a/lib/language_pack.rb b/lib/language_pack.rb
@@ -35,6 +35,7 @@ def self.detect(*args)
 require "language_pack/helpers/rails_runner"
 require "language_pack/helpers/bundler_wrapper"
 require "language_pack/helpers/outdated_ruby_version"
+require "language_pack/helpers/download_presence"
 require "language_pack/installers/ruby_installer"
 require "language_pack/installers/heroku_ruby_installer"
 require "language_pack/installers/rbx_installer"

diff --git a/lib/language_pack/helpers/download_presence.rb b/lib/language_pack/helpers/download_presence.rb
@@ -0,0 +1,67 @@
+# This class is used to check whether a binary exists on one or more stacks.
+# The main motivation for adding this logic is to help people who are upgrading
+# to a new stack if it does not have a given Ruby version. For example if someone
+# is using Ruby 1.9.3 on the cedar-14 stack then they should be informed that it
+# does not exist if they try to use it on the Heroku-18 stack.
+#
+# Example
+#
+#    download = LanguagePack::Helpers::DownloadPresence.new(
+#      'ruby-1.9.3.tgz',
+#      stacks: ['cedar-14', 'heroku-16', 'heroku-18']
+#    )
+#
+#    download.call
+#
+#    puts download.exists? #=> true
+#    puts download.valid_stack_list #=> ['cedar-14']
+class LanguagePack::Helpers::DownloadPresence
+  STACKS = ['cedar-14', 'heroku-16', 'heroku-18']
+
+  def initialize(path, stacks: STACKS)
+    @path = path
+    @stacks = stacks
+    @fetchers = []
+    @threads = []
+    @stacks.each do |stack|
+      @fetchers << LanguagePack::Fetcher.new(LanguagePack::Base::VENDOR_URL, stack)
+    end
+  end
+
+  def next_stack(stack)
+    next_index = @stacks.index(stack) + 1
+
+    @stacks[next_index]
+  end
+
+  def exists_on_next_stack?(stack)
+    next_index = @stacks.index(stack) + 1
+    @threads[next_index]
+  end
+
+  def valid_stack_list
+    raise "not invoked yet, use the `call` method first" if @threads.empty?
+
+    @threads.map.with_index do |thread, i|
+      @stacks[i] if thread.value
+    end.compact
+  end
+
+  def exists?
+    raise "not invoked yet, use the `call` method first" if @threads.empty?
+
+    @threads.any? {|t| t.value }
+  end
+
+  def does_not_exist?
+    !exists?
+  end
+
+  def call
+    @fetchers.map do |fetcher|
+      @threads << Thread.new do
+        fetcher.exists?(@path)
+      end
+    end
+  end
+end
diff --git a/lib/language_pack/installers/heroku_ruby_installer.rb b/lib/language_pack/installers/heroku_ruby_installer.rb
@@ -16,8 +16,7 @@ def fetch_unpack(ruby_version, install_dir, build = false)
     Dir.chdir(install_dir) do
       file = "#{ruby_version.version_for_download}.tgz"
       if build
-        ruby_vm = "ruby"
-        file.sub!(ruby_vm, "#{ruby_vm}-build")
+        file.sub!("ruby", "ruby-build")
       end
       @fetcher.fetch_untar(file)
     end

diff --git a/lib/language_pack/ruby.rb b/lib/language_pack/ruby.rb
@@ -442,10 +442,32 @@ def warn_outdated_ruby
 
       warn_outdated_minor
       warn_outdated_eol
+      warn_stack_upgrade
       true
     end
   end
 
+  def warn_stack_upgrade
+    return if @ruby_download_check.next_stack(stack).nil?
+    return unless @ruby_download_check.exists_on_next_stack?(stack)
+
+    warn(<<~WARNING)
+      Your Ruby version is not present on the next stack
+
+      You are currently using #{ruby_version.version_for_download} on #{stack} stack.
+      This version does not exist on
+      #{@ruby_download_check.next_stack(stack)}. In order to upgrade your stack you will
+      need to upgrade to a supported Ruby version.
+
+      For a list of supported Ruby versions see:
+        https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
+
+      For a list of the oldest Ruby versions present on a given stack see:
+        https://devcenter.heroku.com/articles/ruby-support#oldest-available-runtimes
+
+    WARNING
+  end
+
   def warn_outdated_eol
     return unless @outdated_version_check.maybe_eol?
 
@@ -512,10 +534,15 @@ def install_ruby
     instrument 'ruby.install_ruby' do
       return false unless ruby_version
       installer = LanguagePack::Installers::RubyInstaller.installer(ruby_version).new(@stack)
+      file = "#{ruby_version.version_for_download}.tgz"
 
       if ruby_version.build?
         installer.fetch_unpack(ruby_version, build_ruby_path, true)
+        file.sub!("ruby", "ruby-build")
       end
+      @ruby_download_check = LanguagePack::Helpers::DownloadPresence.new(file)
+      @ruby_download_check.call
+
       installer.install(ruby_version, slug_vendor_ruby)
 
       @outdated_version_check = LanguagePack::Helpers::OutdatedRubyVersion.new(
@@ -538,61 +565,42 @@ def install_ruby
     end
 
     true
-  rescue LanguagePack::Fetcher::FetchError => error
-    if stack == "heroku-18" && ruby_version.version_for_download.match?(/ruby-2\.(2|3)/)
-      message = <<ERROR
-An error occurred while installing #{ruby_version.version_for_download}
-
-This version of Ruby is not available on Heroku-18. The minimum supported version
-of Ruby on the Heroku-18 stack can found at:
-
-  https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
-
-ERROR
+  rescue LanguagePack::Fetcher::FetchError
+    if @ruby_download_check.does_not_exist?
+      message = <<~ERROR
+        The Ruby version you are trying to install does not exist: #{ruby_version.version_for_download}
+      ERROR
+    else
+      message = <<~ERROR
+        The Ruby version you are trying to install does not exist on this stack.
 
-      ci_message = <<ERROR
+        You are trying to install #{ruby_version.version_for_download} on #{stack}.
 
-If you did not intend to build your app for CI on the Heroku-18 stack
-please set your stack version manually in the `app.json`:
+        Ruby #{ruby_version.version_for_download} is present on the following stacks:
 
-```
-"stack": "heroku-16"
-```
+          - #{@ruby_download_check.valid_stack_list.join("\n  - ")}
+      ERROR
 
-More information about this change in behavior can be found at:
-  https://help.heroku.com/3Y1HEXGJ/why-doesn-t-ruby-2-3-7-work-in-my-ci-tests
+      if env("CI")
+        message << <<~ERROR
 
-ERROR
+          On Heroku CI you can set your stack in the `app.json`. For example:
 
-      if env("CI")
-        mcount "fail.bad_version_fetch.heroku-18.ci"
-        message << ci_message
-      else
-        mcount "fail.bad_version_fetch.heroku-18"
+          ```
+          "stack": "heroku-16"
+          ```
+        ERROR
       end
-
-      error message
     end
 
-    mcount "fail.bad_version_fetch"
-    mcount "fail.bad_version_fetch.#{ruby_version.version_for_download}"
-    message = <<ERROR
-An error occurred while installing #{ruby_version.version_for_download}
-
-Heroku recommends you use the latest supported Ruby version listed here:
-  https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
-
-For more information on syntax for declaring a Ruby version see:
-  https://devcenter.heroku.com/articles/ruby-versions
+    message << <<~ERROR
 
-ERROR
-
-    if ruby_version.jruby?
-      message << "Note: Only JRuby 1.7.13 and newer are supported on Cedar-14"
-    end
+      Heroku recommends you use the latest supported Ruby version listed here:
+        https://devcenter.heroku.com/articles/ruby-support#supported-runtimes
 
-    message << "\nDebug Information"
-    message << error.message
+      For more information on syntax for declaring a Ruby version see:
+        https://devcenter.heroku.com/articles/ruby-versions
+    ERROR
 
     error message
   end

diff --git a/spec/helpers/download_presence_spec.rb b/spec/helpers/download_presence_spec.rb
@@ -0,0 +1,66 @@
+require "spec_helper"
+
+describe LanguagePack::Helpers::DownloadPresence do
+  it "knows if exists on the next stack" do
+    download = LanguagePack::Helpers::DownloadPresence.new(
+      'ruby-1.9.3.tgz',
+      stacks: ['cedar-14', 'heroku-16', 'heroku-18']
+    )
+
+    download.call
+
+    expect(download.next_stack("cedar-14")).to eq("heroku-16")
+    expect(download.next_stack("heroku-16")).to eq("heroku-18")
+    expect(download.next_stack("heroku-18")).to be_falsey
+
+    expect(download.exists_on_next_stack?("cedar-14")).to be_truthy
+  end
+
+
+  it "detects when a package is not present on higher stacks" do
+    download = LanguagePack::Helpers::DownloadPresence.new(
+      'ruby-1.9.3.tgz',
+      stacks: ['cedar-14', 'heroku-16', 'heroku-18']
+    )
+
+    download.call
+
+    expect(download.exists?).to eq(true)
+    expect(download.valid_stack_list).to eq(['cedar-14'])
+  end
+
+  it "detects when a package is present on two stacks but not a third" do
+    download = LanguagePack::Helpers::DownloadPresence.new(
+      'ruby-2.3.0.tgz',
+      stacks: ['cedar-14', 'heroku-16', 'heroku-18']
+    )
+
+    download.call
+
+    expect(download.exists?).to eq(true)
+    expect(download.valid_stack_list).to eq(['cedar-14', 'heroku-16'])
+  end
+
+  it "detects when a package does not exist" do
+    download = LanguagePack::Helpers::DownloadPresence.new(
+      'does-not-exist.tgz',
+      stacks: ['cedar-14', 'heroku-16', 'heroku-18']
+    )
+
+    download.call
+
+    expect(download.exists?).to eq(false)
+    expect(download.valid_stack_list).to eq([])
+  end
+
+  it "detects default ruby version" do
+    download = LanguagePack::Helpers::DownloadPresence.new(
+      "#{LanguagePack::RubyVersion::DEFAULT_VERSION}.tgz",
+    )
+
+    download.call
+
+    expect(download.exists?).to eq(true)
+    expect(download.valid_stack_list).to include(LanguagePack::Helpers::DownloadPresence::STACKS.last)
+  end
+end