DEV: Add validator for search_ranking_weights site setting (#20088)

Follow-up to 6934edd97cfdc855d5882e85415b33f573db120c

config/locales/server.en.yml

@@ -2459,6 +2459,7 @@ en:
       delete_rejected_email_after_days: "This setting cannot be set lower than the delete_email_logs_after_days setting or greater than %{max}"
       invalid_uncategorized_category_setting: "The Uncategorized category cannot be selected if allow uncategorized topics is not allowed"
       enable_new_notifications_menu_not_legacy_navigation_menu: "You must set `navigation_menu` to `legacy` before enabling this setting."
+      invalid_search_ranking_weights: "Value is invalid for search_ranking_weights site setting. Example: '{0.1,0.2,0.3,1.0}'. Note that maximum value for each weight is 1.0."
 
     placeholder:
       discourse_connect_provider_secrets:

config/site_settings.yml

@@ -2213,6 +2213,7 @@ search:
   search_ranking_weights:
     default: ""
     hidden: true
+    validator: "SearchRankingWeightsValidator"
   min_search_term_length:
     client: true
     default: 3

lib/validators/search_ranking_weights_validator.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class SearchRankingWeightsValidator
+  def initialize(opts = {})
+    @opts = opts
+  end
+
+  WEIGHT_REGEXP = "1\.0|0\.[0-9]+"
+  WEIGHTS_REGEXP = /{(?<d_weight>#{WEIGHT_REGEXP}),(?<c_weight>#{WEIGHT_REGEXP}),(?<b_weight>#{WEIGHT_REGEXP}),(?<a_weight>#{WEIGHT_REGEXP})}/
+
+  def valid_value?(value)
+    return true if value.blank?
+    value.match(WEIGHTS_REGEXP)
+  end
+
+  def error_message
+    I18n.t("site_settings.errors.invalid_search_ranking_weights")
+  end
+end

spec/lib/validators/search_ranking_weights_validator_spec.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+RSpec.describe SearchRankingWeightsValidator do
+  it 'allows a blank value to be set' do
+    expect do
+      SiteSetting.search_ranking_weights = ''
+    end.not_to raise_error
+  end
+
+  it 'raises the right error when value is invalid' do
+    expect do
+      SiteSetting.search_ranking_weights = 'test'
+    end.to raise_error(Discourse::InvalidParameters, /#{I18n.t("site_settings.errors.invalid_search_ranking_weights")}/)
+
+    expect do
+      SiteSetting.search_ranking_weights = '{1.1,0.1,0.2,0.3}'
+    end.to raise_error(Discourse::InvalidParameters, /#{I18n.t("site_settings.errors.invalid_search_ranking_weights")}/)
+  end
+
+  it 'sets the site setting when value is valid' do
+    expect do
+      SiteSetting.search_ranking_weights = '{0.001,0.2,0.003,1.0}'
+    end.to_not raise_error
+  end
+end