Accept variables parameter as Hash

- Change the format of the variables parameter in the Prometheus proxy
API from an array to a Hash.

- This is because the order of elements in an array parameter is not
guaranteed to be unchanged. Different middleware can seemingly
change the order of elements in an array query parameter.

app/services/prometheus/proxy_variable_substitution_service.rb

@@ -32,8 +32,8 @@ module Prometheus
     def validate_variables(_result)
       return success unless variables
 
-      unless variables.is_a?(Array) && variables.size.even?
-        return error(_('Optional parameter "variables" must be an array of keys and values. Ex: [key1, value1, key2, value2]'))
+      unless variables.is_a?(ActionController::Parameters)
+        return error(_('Optional parameter "variables" must be a Hash. Ex: variables[key1]=value1'))
       end
 
       success
@@ -88,12 +88,7 @@ module Prometheus
     end
 
     def variables_hash
-      # .each_slice(2) converts ['key1', 'value1', 'key2', 'value2'] into
-      # [['key1', 'value1'], ['key2', 'value2']] which is then converted into
-      # a hash by to_h: {'key1' => 'value1', 'key2' => 'value2'}
-      # to_h will raise an ArgumentError if the number of elements in the original
-      # array is not even.
-      variables&.each_slice(2).to_h
+      variables.to_h
     end
 
     def query(result)

locale/gitlab.pot

@@ -15019,7 +15019,7 @@ msgstr ""
 msgid "Optional"
 msgstr ""
 
-msgid "Optional parameter \"variables\" must be an array of keys and values. Ex: [key1, value1, key2, value2]"
+msgid "Optional parameter \"variables\" must be a Hash. Ex: variables[key1]=value1"
 msgstr ""
 
 msgid "Optionally, you can %{link_to_customize} how FogBugz email addresses and usernames are imported into GitLab."

spec/controllers/projects/environments/prometheus_api_controller_spec.rb

@@ -84,12 +84,12 @@ describe Projects::Environments::PrometheusApiController do
 
           before do
             expected_params[:query] = %{up{pod_name="#{pod_name}"}}
-            expected_params[:variables] = ['pod_name', pod_name]
+            expected_params[:variables] = { 'pod_name' => pod_name }
           end
 
           it 'replaces variables with values' do
             get :proxy, params: environment_params.merge(
-              query: 'up{pod_name="{{pod_name}}"}', variables: ['pod_name', pod_name]
+              query: 'up{pod_name="{{pod_name}}"}', variables: { 'pod_name' => pod_name }
             )
 
             expect(response).to have_gitlab_http_status(:success)

spec/services/prometheus/proxy_variable_substitution_service_spec.rb

@@ -64,7 +64,7 @@ describe Prometheus::ProxyVariableSubstitutionService do
       let(:params_keys) do
         {
           query: 'up{pod_name="{{pod_name}}"}',
-          variables: ['pod_name', pod_name]
+          variables: { 'pod_name' => pod_name }
         }
       end
 
@@ -76,7 +76,7 @@ describe Prometheus::ProxyVariableSubstitutionService do
         let(:params_keys) do
           {
             query: 'up{pod_name="{{pod_name}}",env="{{ci_environment_slug}}"}',
-            variables: ['pod_name', pod_name, 'ci_environment_slug', 'custom_value']
+            variables: { 'pod_name' => pod_name, 'ci_environment_slug' => 'custom_value' }
           }
         end
 
@@ -95,8 +95,7 @@ describe Prometheus::ProxyVariableSubstitutionService do
           }
         end
 
-        it_behaves_like 'error', 'Optional parameter "variables" must be an ' \
-          'array of keys and values. Ex: [key1, value1, key2, value2]'
+        it_behaves_like 'error', 'Optional parameter "variables" must be a Hash. Ex: variables[key1]=value1'
       end
 
       context 'with nil variables' do