DEV: Support new discourse-compatibility format on old core (#187)

This introduces a fallback compatibility parser, identical to the one introduced in https://github.com/discourse/discourse/pull/22714

This will allow Docker Manager to parse new compatibility files, even when running on older Discourse instances. This is only intended as a temporary solution, and will be removed before the Discourse 3.2 release.

lib/docker_manager/fallback_compatibility_parser.rb

@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+# This is the compatibility parser introduced in https://github.com/discourse/discourse/pull/22714
+# It's copied here to be used as a fallback when docker_manager is running on an older Discourse version.
+# Should be removed just before the Discourse 3.2 release.
+module DockerManager::FallbackCompatibilityParser
+  def self.find_compatible_resource(version_list, target_version = ::Discourse::VERSION::STRING)
+    return unless version_list.present?
+
+    begin
+      version_list = YAML.safe_load(version_list)
+    rescue Psych::SyntaxError, Psych::DisallowedClass => e
+    end
+
+    raise Discourse::InvalidVersionListError unless version_list.is_a?(Hash)
+
+    version_list =
+      version_list
+        .transform_keys do |v|
+          Gem::Requirement.parse(v)
+        rescue Gem::Requirement::BadRequirementError => e
+          raise Discourse::InvalidVersionListError, "Invalid version specifier: #{v}"
+        end
+        .sort_by do |parsed_requirement, _|
+          operator, version = parsed_requirement
+          [version, operator == "<" ? 0 : 1]
+        end
+
+    parsed_target_version = Gem::Version.new(target_version)
+
+    lowest_matching_entry =
+      version_list.find do |parsed_requirement, target|
+        req_operator, req_version = parsed_requirement
+        req_operator = "<=" if req_operator == "="
+
+        if !%w[<= <].include?(req_operator)
+          raise Discourse::InvalidVersionListError,
+                "Invalid version specifier operator for '#{req_operator} #{req_version}'. Operator must be one of <= or <"
+        end
+
+        resolved_requirement = Gem::Requirement.new("#{req_operator} #{req_version.to_s}")
+        resolved_requirement.satisfied_by?(parsed_target_version)
+      end
+
+    return if lowest_matching_entry.nil?
+
+    checkout_version = lowest_matching_entry[1]
+
+    begin
+      Discourse::Utils.execute_command "git",
+                                       "check-ref-format",
+                                       "--allow-onelevel",
+                                       checkout_version
+    rescue RuntimeError
+      raise Discourse::InvalidVersionListError, "Invalid ref name: #{checkout_version}"
+    end
+
+    checkout_version
+  end
+
+  # Find a compatible resource from a git repo
+  def self.find_compatible_git_resource(path)
+    return unless File.directory?("#{path}/.git")
+    compat_resource, std_error, s =
+      Open3.capture3(
+        "git -C '#{path}' show HEAD@{upstream}:#{Discourse::VERSION_COMPATIBILITY_FILENAME}",
+      )
+    self.find_compatible_resource(compat_resource) if s.success?
+  rescue Discourse::InvalidVersionListError => e
+    $stderr.puts "Invalid version list in #{path}"
+  end
+end

lib/docker_manager/git_repo.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require_relative "fallback_compatibility_parser"
+
 # like Grit just very very minimal
 class DockerManager::GitRepo
   attr_reader :path, :name, :branch
@@ -129,10 +131,13 @@ class DockerManager::GitRepo
   end
 
   def tracking_branch
-    branch = nil
+    branch =
-    if defined?(Discourse.find_compatible_git_resource)
+      begin
-      branch = Discourse.find_compatible_git_resource(path)
+        Discourse.find_compatible_git_resource(path)
-    end
+      rescue ArgumentError
+        DockerManager::FallbackCompatibilityParser.find_compatible_git_resource(path)
+      end
+
     return branch if branch.present?
 
     head = upstream_branch