FIX: themes:update rake task not rolling back transaction on error (#26750)

This commit fixes a bug in the `themes:update` rake task which resulted
in the ActiveRecord transaction not being rolled back when an error was
encountered. The transaction was first introduced in
7f0682f4f23150890ec93452bac0da21c9d5938a which changed a `begin..rescue`
block to `transaction do..rescue`. The problem with that change
prevented the transaction from ever rolling back as the code block
looks something like this:

```
transaction do
  begin
    update_theme
  rescue => e
    # surpress error
  end
end
```

From the transaction's point of view now, it will never rollback even if
an error was encountered when updating the remote theme because it will
never see the error.

Instead we should have done something like this if we wanted to surpress
the errors encountered while still ensuring that the transaction is
rolled back.

```
begin
  transaction do
    update_theme
  end
rescue => e
  # surpress error
end
```

lib/tasks/themes.rake

@@ -62,26 +62,28 @@ def update_themes
     .includes(:remote_theme)
     .where(enabled: true, auto_update: true)
     .find_each do |theme|
-      theme.transaction do
-        remote_theme = theme.remote_theme
-        next if remote_theme.blank? || remote_theme.remote_url.blank?
+      begin
+        theme.transaction do
+          remote_theme = theme.remote_theme
+          next if remote_theme.blank? || remote_theme.remote_url.blank?
 
-        print "Checking '#{theme.name}' for '#{RailsMultisite::ConnectionManagement.current_db}'... "
+          print "Checking '#{theme.name}' for '#{RailsMultisite::ConnectionManagement.current_db}'... "
 
-        remote_theme.update_remote_version
+          remote_theme.update_remote_version
 
-        if remote_theme.out_of_date?
-          puts "updating from #{remote_theme.local_version[0..7]} to #{remote_theme.remote_version[0..7]}"
-          remote_theme.update_from_remote(already_in_transaction: true)
-        else
-          puts "up to date"
-        end
+          if remote_theme.out_of_date?
+            puts "updating from #{remote_theme.local_version[0..7]} to #{remote_theme.remote_version[0..7]}"
+            remote_theme.update_from_remote(already_in_transaction: true)
+          else
+            puts "up to date"
+          end
 
-        if remote_theme.last_error_text.present?
-          raise RemoteTheme::ImportError.new(remote_theme.last_error_text)
+          if remote_theme.last_error_text.present?
+            raise RemoteTheme::ImportError.new(remote_theme.last_error_text)
+          end
         end
       rescue => e
-        STDERR.puts "[#{RailsMultisite::ConnectionManagement.current_db}] Failed to update '#{theme.name}' (#{theme.id}): #{e}"
+        $stderr.puts "[#{RailsMultisite::ConnectionManagement.current_db}] Failed to update '#{theme.name}' (#{theme.id}): #{e}"
         raise if ENV["RAISE_THEME_ERRORS"] == "1"
       end
     end

spec/tasks/themes_spec.rb

@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+RSpec.describe "tasks/themes" do
+  before do
+    Rake::Task.clear
+    Discourse::Application.load_tasks
+  end
+
+  describe "themes:update" do
+    let(:initial_repo) do
+      about_json = <<~JSON
+      {
+        "name": "awesome theme",
+        "about_url": "https://www.site.com/about",
+        "license_url": "https://www.site.com/license",
+        "theme_version": "1.0",
+        "minimum_discourse_version": "1.0.0"
+      }
+      JSON
+
+      setup_git_repo("about.json" => about_json, "common/header.html" => "I AM A HEADER")
+    end
+
+    let(:initial_repo_url) do
+      MockGitImporter.register("https://example.com/initial_repo.git", initial_repo)
+    end
+
+    let!(:theme) { RemoteTheme.import_theme(initial_repo_url) }
+
+    around(:each) { |group| MockGitImporter.with_mock { group.run } }
+
+    after { `rm -fr #{initial_repo}` }
+
+    it "should not update the theme if a theme setting migration fails during the update" do
+      migration_content = <<~JS
+      export default function migrate(settings) {
+        throw "error";
+      }
+      JS
+
+      add_to_git_repo(
+        initial_repo,
+        "migrations/settings/0001-a-migration.js" => migration_content,
+        "common/header.html" => "I AM UPDATED HEADER",
+      )
+
+      original_remote_version = theme.remote_theme.remote_version
+      original_local_version = theme.remote_theme.local_version
+
+      capture_stderr { capture_stdout { Rake::Task["themes:update"].invoke } }
+
+      theme.reload
+
+      expect(theme.theme_fields.count).to eq(1)
+      expect(theme.theme_fields.where(name: "header").first.value).to eq("I AM A HEADER")
+      expect(theme.theme_settings_migrations.count).to eq(0)
+      expect(theme.remote_theme.commits_behind).to eq(0)
+      expect(theme.remote_theme.remote_version).to eq(original_remote_version)
+      expect(theme.remote_theme.local_version).to eq(original_local_version)
+    end
+  end
+end