workaround for dry-rb#618

lib/dry/validation/message.rb

@@ -85,6 +85,19 @@ def base?
         @base ||= path.compact.empty?
       end
 
+      # Build full message
+      #
+      # @return [Message]
+      #
+      # @api public
+      def full_message
+        if base?
+          self
+        else
+          Message["#{path.compact.join(',')} #{text}", path, meta]
+        end
+      end
+
       # Dump error to a string
       #
       # @return [String]

lib/dry/validation/message_set.rb

@@ -41,7 +41,8 @@ def with(other, new_options = EMPTY_HASH)
         return self if new_options.empty? && other.eql?(messages)
 
         self.class.new(
-          other | select { |err| err.is_a?(Message) },
+          other | select { |err| err.is_a?(Message) }
+                  .map {|err| new_options.fetch(:full, false) ? err.full_message : err },
           options.merge(source: source_messages, **new_options)
         ).freeze
       end

spec/unit/rule_spec.rb

@@ -23,5 +23,19 @@
         tags: ['must have at least 1 element']
       )
     end
+
+    it 'shows the correct error message' do
+      contract_class.rule(:tags) do
+        key.failure('must have at least 1 element') unless value.size > 0
+      end
+
+      expect(contract.(tags: [], name: '').errors.to_h).to eql(
+        tags: ['must have at least 1 element']
+      )
+
+      expect(contract.(tags: [], name: '').errors(full: true).to_h).to eql(
+        tags: ['tags must have at least 1 element']
+      )
+    end
   end
 end