Render deprecations for arguments correctly

This uses the schema to pre-compute a lookup table for deprecation
information.

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/326302

lib/gitlab/graphql/docs/helper.rb

@@ -242,7 +242,7 @@ module Gitlab
 
         def render_name(object, owner = nil)
           rendered_name = "`#{object[:name]}`"
-          rendered_name += ' **{warning-solid}**' if object[:is_deprecated]
+          rendered_name += ' **{warning-solid}**' if deprecated?(object, owner)
 
           return rendered_name unless owner
 
@@ -255,13 +255,20 @@ module Gitlab
         # Returns the object description. If the object has been deprecated,
         # the deprecation reason will be returned in place of the description.
         def render_description(object, owner = nil, context = :block)
-          if object[:is_deprecated]
+          if deprecated?(object, owner)
             render_deprecation(object, owner, context)
           else
             render_description_of(object)
           end
         end
 
+        def deprecated?(object, owner)
+          return true if object[:is_deprecated] # only populated for fields, not arguments!
+
+          key = [*Array.wrap(owner), object[:name]].join('.')
+          deprecations.key?(key)
+        end
+
         def render_description_of(object)
           desc = if object[:is_edge]
                    base = object[:name].chomp('Edge')
@@ -280,7 +287,6 @@ module Gitlab
         end
 
         def render_deprecation(object, owner, context)
-          owner = Array.wrap(owner)
           buff = []
           deprecation = schema_deprecation(owner, object[:name])
 
@@ -356,38 +362,8 @@ module Gitlab
         # returns the deprecation information for a field or argument
         # See: Gitlab::Graphql::Deprecation
         def schema_deprecation(type_name, field_name)
-          schema_member(type_name, field_name)&.deprecation
-        end
-
-        # Return a part of the schema.
-        #
-        # This queries the Schema by owner and name to find:
-        #
-        # - fields (e.g. `schema_member('Query', 'currentUser')`)
-        # - arguments (e.g. `schema_member(['Query', 'project], 'fullPath')`)
-        def schema_member(type_name, field_name)
-          type_name = Array.wrap(type_name)
-          if type_name.size == 2
-            arg_name = field_name
-            type_name, field_name = type_name
-          else
-            type_name = type_name.first
-            arg_name = nil
-          end
-
-          return if type_name.nil? || field_name.nil?
-
-          type = schema.types[type_name]
-          return unless type && type.kind.fields?
-
-          field = type.fields[field_name]
-          return field if arg_name.nil?
-
-          args = field.arguments
-          is_mutation = field.mutation && field.mutation <= ::Mutations::BaseMutation
-          args = args['input'].type.unwrap.arguments if is_mutation
-
-          args[arg_name]
+          key = [*Array.wrap(type_name), field_name].join('.')
+          deprecations[key]
         end
 
         def render_input_type(query)
@@ -396,6 +372,25 @@ module Gitlab
 
           "Input type: `#{input_field[:type][:name]}`."
         end
+
+        def deprecations
+          strong_memoize(:deprecations) do
+            mapping = {}
+
+            schema.types.each do |type_name, type|
+              next unless type.kind.fields?
+
+              type.fields.each do |field_name, field|
+                mapping["#{type_name}.#{field_name}"] = field.try(:deprecation)
+                field.arguments.each do |arg_name, arg|
+                  mapping["#{type_name}.#{field_name}.#{arg_name}"] = arg.try(:deprecation)
+                end
+              end
+            end
+
+            mapping.compact
+          end
+        end
       end
     end
   end

spec/lib/gitlab/graphql/docs/renderer_spec.rb

@@ -150,6 +150,43 @@ RSpec.describe Gitlab::Graphql::Docs::Renderer do
       end
     end
 
+    context 'when an argument is deprecated' do
+      let(:type) do
+        Class.new(Types::BaseObject) do
+          graphql_name 'DeprecatedTest'
+          description 'A thing we used to use, but no longer support'
+
+          field :foo,
+                type: GraphQL::STRING_TYPE,
+                null: false,
+                description: 'A description.' do
+                  argument :foo_arg, GraphQL::STRING_TYPE,
+                           required: false,
+                           description: 'The argument.',
+                           deprecated: { reason: 'Bad argument', milestone: '101.2' }
+                end
+        end
+      end
+
+      let(:section) do
+        <<~DOC
+         ##### `DeprecatedTest.foo`
+
+         A description.
+
+         Returns [`String!`](#string).
+
+         ###### Arguments
+
+         | Name | Type | Description |
+         | ---- | ---- | ----------- |
+         | <a id="deprecatedtestfoofooarg"></a>`fooArg` **{warning-solid}** | [`String`](#string) | **Deprecated** in 101.2. Bad argument. |
+        DOC
+      end
+
+      it_behaves_like 'renders correctly as GraphQL documentation'
+    end
+
     context 'when a field is deprecated' do
       let(:type) do
         Class.new(Types::BaseObject) do
@@ -338,11 +375,31 @@ RSpec.describe Gitlab::Graphql::Docs::Renderer do
                           required: true,
                           description: 'How much prettier?'
 
+        mutation.argument :pulchritude,
+                          type: GraphQL::FLOAT_TYPE,
+                          required: false,
+                          description: 'How much prettier?',
+                          deprecated: {
+                            reason: :renamed,
+                            replacement: 'prettinessFactor',
+                            milestone: '72.34'
+                          }
+
         mutation.field :everything,
                        type: GraphQL::STRING_TYPE,
                        null: true,
                        description: 'What we made prettier.'
 
+        mutation.field :omnis,
+                       type: GraphQL::STRING_TYPE,
+                       null: true,
+                       description: 'What we made prettier.',
+                       deprecated: {
+                         reason: :renamed,
+                         replacement: 'everything',
+                         milestone: '72.34'
+                       }
+
         mutation
       end
 
@@ -365,6 +422,7 @@ RSpec.describe Gitlab::Graphql::Docs::Renderer do
             | ---- | ---- | ----------- |
             | <a id="mutationmakeitprettyclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
             | <a id="mutationmakeitprettyprettinessfactor"></a>`prettinessFactor` | [`Float!`](#float) | How much prettier?. |
+            | <a id="mutationmakeitprettypulchritude"></a>`pulchritude` **{warning-solid}** | [`Float`](#float) | **Deprecated:** This was renamed. Please use `prettinessFactor`. Deprecated in 72.34. |
 
             #### Fields
 
@@ -373,6 +431,7 @@ RSpec.describe Gitlab::Graphql::Docs::Renderer do
             | <a id="mutationmakeitprettyclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
             | <a id="mutationmakeitprettyerrors"></a>`errors` | [`[String!]!`](#string) | Errors encountered during execution of the mutation. |
             | <a id="mutationmakeitprettyeverything"></a>`everything` | [`String`](#string) | What we made prettier. |
+            | <a id="mutationmakeitprettyomnis"></a>`omnis` **{warning-solid}** | [`String`](#string) | **Deprecated:** This was renamed. Please use `everything`. Deprecated in 72.34. |
           DOC
         end
       end