Improve error reporting on users API

* users (#6878, #3526, #4209): Validation error messages are now exposed through 400 responses, 409 response are sent in case of duplicate email or username
* MRs (#5335): 409 responses are sent in case of duplicate merge request (source/target branches), 422 responses are sent when submiting MR fo/from unrelated forks
* issues
* labels
* projects

1 files changed, 13 insertions, 18 deletions

diff --git a/lib/api/labels.rb b/lib/api/labels.rb
index 2fdf53ffec2..78ca58ad0d1 100644
--- a/lib/api/labels.rb
+++ b/lib/api/labels.rb
@@ -30,16 +30,14 @@ module API
         attrs = attributes_for_keys [:name, :color]
         label = user_project.find_label(attrs[:name])
 
-        if label
-          return render_api_error!('Label already exists', 409)
-        end
+        conflict!('Label already exists') if label
 
         label = user_project.labels.create(attrs)
 
         if label.valid?
           present label, with: Entities::Label
         else
-          render_api_error!(label.errors.full_messages.join(', '), 400)
+          render_validation_error!(label)
         end
       end
 
@@ -56,9 +54,7 @@ module API
         required_attributes! [:name]
 
         label = user_project.find_label(params[:name])
-        if !label
-          return render_api_error!('Label not found', 404)
-        end
+        not_found!('Label') unless label
 
         label.destroy
       end
@@ -66,10 +62,11 @@ module API
       # Updates an existing label. At least one optional parameter is required.
       #
       # Parameters:
-      #   id    (required) - The ID of a project
-      #   name  (optional) - The name of the label to be deleted
-      #   color (optional) - Color of the label given in 6-digit hex
-      #                      notation with leading '#' sign (e.g. #FFAABB)
+      #   id        (required) - The ID of a project
+      #   name      (required) - The name of the label to be deleted
+      #   new_name  (optional) - The new name of the label
+      #   color     (optional) - Color of the label given in 6-digit hex
+      #                          notation with leading '#' sign (e.g. #FFAABB)
       # Example Request:
       #   PUT /projects/:id/labels
       put ':id/labels' do
@@ -77,16 +74,14 @@ module API
         required_attributes! [:name]
 
         label = user_project.find_label(params[:name])
-        if !label
-          return render_api_error!('Label not found', 404)
-        end
+        not_found!('Label not found') unless label
 
         attrs = attributes_for_keys [:new_name, :color]
 
         if attrs.empty?
-          return render_api_error!('Required parameters "name" or "color" ' \
-                                   'missing',
-                                   400)
+          render_api_error!('Required parameters "new_name" or "color" ' \
+                            'missing',
+                            400)
         end
 
         # Rename new name to the actual label attribute name
@@ -95,7 +90,7 @@ module API
         if label.update(attrs)
           present label, with: Entities::Label
         else
-          render_api_error!(label.errors.full_messages.join(', '), 400)
+          render_validation_error!(label)
         end
       end
     end